Document And Entity Information - USD ($)	12 Months Ended
Document And Entity Information - USD ($)	Dec. 31, 2017	Feb. 16, 2018	Jun. 30, 2017
Document Information [Line Items]
Entity Registrant Name	Great Plains Energy Inc
Entity Central Index Key	0001143068
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 6,311,042,442
Entity Common Stock, Shares Outstanding		215,665,193
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q4
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Revenues
Electric revenues	$ 2,708.2	$ 2,676.0	$ 2,502.2
Operating Expenses
Fuel and purchased power	608.6	590.1	608.7
Transmission	105.7	84.8	89.1
Utility operating and maintenance expenses	754.2	759.5	724.8
Costs to achieve the anticipated merger with Westar Energy, Inc.	31.8	34.2	0.0
Depreciation and amortization	371.1	344.8	330.4
General taxes	229.2	226.7	213.2
Other	4.0	17.0	5.9
Total	2,104.6	2,057.1	1,972.1
Operating income	603.6	618.9	530.1
Other Income (Expense)
Non-operating income	50.7	17.1	11.7
Non-operating expenses	(31.4)	(14.3)	(8.0)
Loss on Series B Preferred Stock dividend make-whole provisions [Note 14]	(124.8)	0.0	0.0
Loss on extinguishment of debt (Note 12)	(82.8)	0.0	0.0
Total	(188.3)	2.8	3.7
Interest charges	(290.7)	(161.5)	(199.3)
Income before income tax expense and income from equity investments	124.6	460.2	334.5
Income tax expense	(233.3)	(172.2)	(122.7)
Income from equity investments, net of income taxes	2.5	2.0	1.2
Net income (loss)	(106.2)	290.0	213.0
Preferred stock dividend requirements and redemption premium	37.3	16.5	1.6
Earnings (loss) available for common shareholders	$ (143.5)	$ 273.5	$ 211.4
Average number of basic common shares outstanding	215.5	169.4	154.2
Average number of diluted common shares outstanding	215.5	169.8	154.8
Basic and diluted earnings (loss) per common share	$ (0.67)	$ 1.61	$ 1.37
Cash dividends per common share	$ 1.100	$ 1.0625	$ 0.9975
Comprehensive Income
Net income (loss)	$ (106.2)	$ 290.0	$ 213.0
Derivative hedging activity
Reclassification to expenses, net of tax	4.9	5.6	5.7
Derivative hedging activity, net of tax	4.9	5.6	5.7
Defined benefit pension plans
Net gain (loss) arising during period	(0.7)	(1.1)	1.0
Income tax (expense) benefit	(0.2)	0.4	(0.4)
Net gain (loss) arising during period, net of tax	(0.9)	(0.7)	0.6
Amortization of net losses included in net periodic benefit costs, net of tax	0.4	0.5	0.4
Change in unrecognized pension expense, net of tax	(0.5)	(0.2)	1.0
Total other comprehensive income	4.4	5.4	6.7
Comprehensive income (loss)	(101.8)	295.4	219.7
KCPL [Member]
Operating Revenues
Electric revenues	1,890.7	1,875.4	1,713.8
Operating Expenses
Fuel and purchased power	412.1	372.7	397.1
Transmission	68.6	56.4	58.4
Utility operating and maintenance expenses	506.4	525.8	494.2
Costs to achieve the anticipated merger with Westar Energy, Inc.	10.5	10.9	0.0
Depreciation and amortization	266.3	247.5	235.7
General taxes	182.5	177.5	163.5
Other	0.6	2.5	0.9
Total	1,447.0	1,393.3	1,349.8
Operating income	443.7	482.1	364.0
Other Income (Expense)
Non-operating income	11.2	11.8	8.4
Non-operating expenses	(8.1)	(7.6)	(7.2)
Total	3.1	4.2	1.2
Interest charges	(138.8)	(139.4)	(135.6)
Income before income tax expense and income from equity investments	308.0	346.9	229.6
Income tax expense	(128.2)	(121.9)	(76.8)
Net income (loss)	179.8	225.0	152.8
Comprehensive Income
Net income (loss)	179.8	225.0	152.8
Derivative hedging activity
Reclassification to expenses, net of tax	4.6	5.4	5.3
Derivative hedging activity, net of tax	4.6	5.4	5.3
Defined benefit pension plans
Total other comprehensive income	4.6	5.4	5.3
Comprehensive income (loss)	$ 184.4	$ 230.4	$ 158.1

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 1,125.4	$ 1,293.1
Time deposit	0.0	1,000.0
Receivables, net	151.7	166.0
Accounts receivable pledged as collateral	180.0	172.4
Fuel inventories, at average cost	103.2	108.8
Materials and supplies, at average cost	171.2	162.2
Deferred refueling outage costs	6.8	22.3
Interest rate derivative instruments	91.4	79.3
Prepaid expenses and other assets	33.4	55.4
Total	1,863.1	3,059.5
Utility Plant, at Original Cost
Electric	13,674.1	13,597.7
Less - accumulated depreciation	5,224.0	5,106.9
Net utility plant in service	8,450.1	8,490.8
Construction work in progress	458.6	403.9
Plant to be retired, net	143.6	0.0
Nuclear fuel, net of amortization of $204.2 and $172.1	72.4	62.0
Total	9,124.7	8,956.7
Investments and Other Assets
Nuclear decommissioning trust fund	258.4	222.9
Regulatory assets	913.9	1,048.0
Goodwill	169.0	169.0
Other	128.8	113.9
Total	1,470.1	1,553.8
Total	12,457.9	13,570.0
Current Liabilities
Notes payable	11.0	0.0
Collateralized note payable	180.0	172.4
Commercial paper	376.8	334.8
Current maturities of long-term debt	351.1	382.1
Accounts payable	340.0	323.7
Accrued taxes	35.1	33.3
Accrued interest	42.8	50.8
Accrued compensation and benefits	50.1	52.1
Pension and post-retirement liability	2.7	3.0
Other	59.2	32.6
Total	1,448.8	1,384.8
Deferred Credits and Other Liabilities
Deferred income taxes	621.7	1,329.7
Deferred tax credits	124.8	126.2
Asset retirement obligations	262.5	316.0
Pension and post-retirement liability	535.0	488.3
Regulatory liabilities	1,106.3	309.9
Other	81.4	87.9
Total	2,731.7	2,658.0
Shareholders' equity
Common stock	4,233.1	4,217.0
Preference Stock	0.0	836.2
Retained earnings	737.9	1,119.2
Treasury stock - 137,589 and 128,087 shares, at cost	(4.0)	(3.8)
Accumulated other comprehensive loss	(2.2)	(6.6)
Total shareholders' equity	4,964.8	6,162.0
Long-term debt (Note 12)	3,312.6	3,365.2
Total	8,277.4	9,527.2
Commitments and Contingencies (Note 15)
Total	12,457.9	13,570.0
KCPL [Member]
Current Assets
Cash and cash equivalents	2.2	4.5
Receivables, net	106.3	139.1
Related party receivables	84.7	67.2
Accounts receivable pledged as collateral	130.0	110.0
Fuel inventories, at average cost	71.0	72.9
Materials and supplies, at average cost	126.0	118.9
Deferred refueling outage costs	6.8	22.3
Refundable income taxes	5.4	12.7
Prepaid expenses and other assets	27.6	27.9
Total	560.0	575.5
Utility Plant, at Original Cost
Electric	10,213.2	9,925.1
Less - accumulated depreciation	4,070.3	3,858.4
Net utility plant in service	6,142.9	6,066.7
Construction work in progress	350.3	300.4
Nuclear fuel, net of amortization of $204.2 and $172.1	72.4	62.0
Total	6,565.6	6,429.1
Investments and Other Assets
Nuclear decommissioning trust fund	258.4	222.9
Regulatory assets	691.9	801.8
Other	48.0	29.1
Total	998.3	1,053.8
Total	8,123.9	8,058.4
Current Liabilities
Collateralized note payable	130.0	110.0
Commercial paper	167.5	132.9
Current maturities of long-term debt	350.0	281.0
Accounts payable	249.0	231.6
Accrued taxes	29.0	27.0
Accrued interest	32.4	32.4
Accrued compensation and benefits	50.1	52.1
Pension and post-retirement liability	1.4	1.6
Other	46.8	11.4
Total	1,056.2	880.0
Deferred Credits and Other Liabilities
Deferred income taxes	616.1	1,228.3
Deferred tax credits	121.8	122.8
Asset retirement obligations	231.4	278.0
Pension and post-retirement liability	512.2	465.8
Regulatory liabilities	779.2	187.4
Other	61.6	70.6
Total	2,322.3	2,352.9
Shareholders' equity
Common stock	1,563.1	1,563.1
Retained earnings	949.7	982.6
Accumulated other comprehensive loss	0.4	(4.2)
Total shareholders' equity	2,513.2	2,541.5
Long-term debt (Note 12)	2,232.2	2,284.0
Total	4,745.4	4,825.5
Commitments and Contingencies (Note 15)
Total	$ 8,123.9	$ 8,058.4

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 204.2	$ 172.1
Shareholder's equity
Common stock - shares authorized (in shares)	600,000,000	600,000,000
Common stock-shares issued (in shares)	215,801,723	215,479,105
Treasury stock- shares (in shares)	137,589	128,087
KCPL [Member]
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 204.2	$ 172.1
Shareholder's equity
Common stock - shares authorized (in shares)	1,000.0	1,000.0
Common stock-shares issued (in shares)	1.0	1.0
Series B Preferred Stock [Member]
Shareholder's equity
Preferred Stock, Shares Issued	0	862,500
Preferred Stock, Dividend Rate, Percentage	7.00%	7.00%
Preferred Stock, Liquidation Preference Per Share	$ 1,000.00	$ 1,000.00

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities
Net income (loss)	$ (106.2)	$ 290.0	$ 213.0
Adjustments to reconcile income (loss) to net cash from operating activities:
Depreciation and amortization	371.1	344.8	330.4
Amortization of:
Nuclear fuel	32.1	26.6	26.8
Other	63.9	77.5	47.7
Deferred income taxes, net	235.4	170.1	124.9
Investment tax credit amortization	(1.4)	(1.4)	(1.4)
Income from equity investments, net of income taxes	(2.5)	(2.0)	(1.2)
Fair value impacts of interest rate swaps	(12.1)	(79.3)	0.0
Loss on Series B Preferred Stock dividend make-whole provisions (Note 14)	124.8	0.0	0.0
Loss on extinguishment of debt (Note 12)	82.8	0.0	0.0
Other operating activities (Note 3)	22.6	(42.3)	12.9
Net cash from operating activities	810.5	784.0	753.1
Cash Flows from Investing Activities
Utility capital expenditures	(573.5)	(609.4)	(677.1)
Allowance for borrowed funds used during construction	(7.4)	(6.8)	(5.8)
Purchases of nuclear decommissioning trust investments	(33.6)	(31.9)	(50.9)
Proceeds from nuclear decommissioning trust investments	30.3	28.6	47.6
Purchase of time deposit	0.0	(1,000.0)	0.0
Proceeds from time deposit	1,000.0	0.0	0.0
Other investing activities	(45.6)	(64.0)	(48.2)
Net cash from investing activities	370.2	(1,683.5)	(734.4)
Cash Flows from Financing Activities
Issuance of common stock	2.9	1,603.7	3.0
Issuance of preferred stock	0.0	862.5	0.0
Issuance of long-term debt	4,591.1	0.0	348.8
Proceeds from issuance of long-term debt from remarketing	0.0	0.0	146.5
Repayment of long-term debt from remarketing	0.0	0.0	(146.5)
Issuance fees	(38.3)	(143.6)	(3.0)
Repayment of long-term debt, including redemption premium	(4,725.1)	(1.1)	(87.0)
Net change in short-term borrowings	53.0	100.8	(128.3)
Net change in collateralized short-term borrowings	7.6	(2.6)	4.0
Dividends paid	(272.0)	(194.0)	(155.5)
Redemption of preferred stock	(963.4)	(40.1)	0.0
Other financing activities	(4.2)	(4.3)	(2.4)
Net cash from financing activities	(1,348.4)	2,181.3	(20.4)
Net Change in Cash and Cash Equivalents	(167.7)	1,281.8	(1.7)
Cash and Cash Equivalents at Beginning of Year	1,293.1	11.3	13.0
Cash and Cash Equivalents at End of Year	1,125.4	1,293.1	11.3
KCPL [Member]
Cash Flows from Operating Activities
Net income (loss)	179.8	225.0	152.8
Adjustments to reconcile income (loss) to net cash from operating activities:
Depreciation and amortization	266.3	247.5	235.7
Amortization of:
Nuclear fuel	32.1	26.6	26.8
Other	30.2	33.9	29.1
Deferred income taxes, net	83.5	93.4	99.4
Investment tax credit amortization	(1.0)	(1.0)	(1.0)
Other operating activities (Note 3)	20.0	(2.1)	(61.5)
Net cash from operating activities	610.9	623.3	481.3
Cash Flows from Investing Activities
Utility capital expenditures	(437.7)	(418.8)	(518.3)
Allowance for borrowed funds used during construction	(6.1)	(5.6)	(3.9)
Purchases of nuclear decommissioning trust investments	(33.6)	(31.9)	(50.9)
Proceeds from nuclear decommissioning trust investments	30.3	28.6	47.6
Other investing activities	(23.9)	(23.8)	(25.5)
Net cash from investing activities	(471.0)	(451.5)	(551.0)
Cash Flows from Financing Activities
Issuance of long-term debt	299.2	0.0	348.8
Proceeds from issuance of long-term debt from remarketing	0.0	0.0	146.5
Repayment of long-term debt from remarketing	0.0	0.0	(146.5)
Issuance fees	(3.0)	(0.2)	(3.0)
Repayment of long-term debt, including redemption premium	(281.0)	0.0	(85.9)
Net change in short-term borrowings	34.6	(47.4)	(178.0)
Net change in collateralized short-term borrowings	20.0	0.0	0.0
Net money pool borrowings	0.0	0.0	(12.6)
Dividends paid	(212.0)	(122.0)	0.0
Net cash from financing activities	(142.2)	(169.6)	69.3
Net Change in Cash and Cash Equivalents	(2.3)	2.2	(0.4)
Cash and Cash Equivalents at Beginning of Year	4.5	2.3	2.7
Cash and Cash Equivalents at End of Year	$ 2.2	$ 4.5	$ 2.3

Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Preferred Stock [Member] Cumulative Preferred Stock [Member]	Preferred Stock [Member] Preference Stock [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	KCPL [Member]	KCPL [Member] Common Stock [Member]	KCPL [Member] Retained Earnings [Member]	KCPL [Member] Accumulated Other Comprehensive Income (Loss) [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU 2016-09 (Note 1)										$ 0.0
Beginning balance at Dec. 31, 2014		$ 2,639.3	$ 39.0	$ 0.0	$ 967.8	$ (2.3)	$ (18.7)		$ 1,563.1	726.8	$ (14.9)
Beginning balance (in shares) at Dec. 31, 2014		154,254,037	390,000	0					1
Beginning balance, treasury stock (in shares) at Dec. 31, 2014						(91,281)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock		$ 6.6		$ 0.0
Issuance of stock (in shares)		250,863		0
Equity compensation expense, net of forfeitures		$ 1.9
Redemption of preferred stock			$ 0.0	$ 0.0
Redemption of preferred stock (in shares)			0	0
Unearned Compensation [Abstract]
Issuance of restricted common stock		(2.4)
Forfeiture of restricted common stock		0.5
Compensation expense recognized		1.8
Other		(1.0)
Net income (loss)	$ 213.0				213.0			$ 152.8		152.8
Redemption premium on preferred stock					0.0
Dividends:
Common stock ($1.10, $1.0625 and $0.9975 per share)					(153.9)					0.0
Preferred stock - at required rates					(1.6)
Performance shares					(0.9)
Treasury shares acquired						$ (2.0)
Treasury shares acquired (in shares)						(76,468)
Treasury shares reissued						$ 1.7
Treasury shares reissued (in shares)						66,520
Derivative hedging activity, net of tax	5.7						5.7	5.3			5.3
Change in unrecognized pension expense, net of tax	1.0						1.0
Ending balance at Dec. 31, 2015	3,695.5	$ 2,646.7	$ 39.0	$ 0.0	1,024.4	$ (2.6)	(12.0)	2,433.1	$ 1,563.1	879.6	(9.6)
Ending balance, treasury stock (in shares) at Dec. 31, 2015						(101,229)
Ending balance (in shares) at Dec. 31, 2015		154,504,900	390,000	0					1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU 2016-09 (Note 1)										0.0
Issuance of stock		$ 1,565.3		$ 836.2
Issuance of stock (in shares)		60,974,205		862,500
Equity compensation expense, net of forfeitures		$ 4.3
Redemption of preferred stock			$ (39.0)	$ 0.0
Redemption of preferred stock (in shares)			(390,000)	0
Unearned Compensation [Abstract]
Issuance of restricted common stock		(2.8)
Forfeiture of restricted common stock		0.0
Compensation expense recognized		2.7
Other		0.8
Net income (loss)	290.0				290.0			225.0		225.0
Redemption premium on preferred stock					(0.6)
Dividends:
Common stock ($1.10, $1.0625 and $0.9975 per share)					(181.0)					(122.0)
Preferred stock - at required rates					(13.0)
Performance shares					(0.6)
Treasury shares acquired						$ (4.1)
Treasury shares acquired (in shares)						(138,021)
Treasury shares reissued						$ 2.9
Treasury shares reissued (in shares)						111,163
Derivative hedging activity, net of tax	5.6						5.6	5.4			5.4
Change in unrecognized pension expense, net of tax	(0.2)						(0.2)
Ending balance at Dec. 31, 2016	$ 6,162.0	$ 4,217.0	$ 0.0	$ 836.2	1,119.2	$ (3.8)	(6.6)	2,541.5	$ 1,563.1	982.6	(4.2)
Ending balance, treasury stock (in shares) at Dec. 31, 2016	(128,087)					(128,087)
Ending balance (in shares) at Dec. 31, 2016		215,479,105	0	862,500					1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU 2016-09 (Note 1)										(0.7)
Issuance of stock		$ 11.7		$ 0.0
Issuance of stock (in shares)		322,618		0
Equity compensation expense, net of forfeitures		$ 5.4
Redemption of preferred stock			$ 0.0	$ (836.2)
Redemption of preferred stock (in shares)			0	(862,500)
Unearned Compensation [Abstract]
Issuance of restricted common stock		(2.3)
Forfeiture of restricted common stock		0.7
Compensation expense recognized		2.1
Other		(1.5)
Net income (loss)	$ (106.2)				(106.2)			179.8		179.8
Redemption premium on preferred stock					(2.4)
Dividends:
Common stock ($1.10, $1.0625 and $0.9975 per share)					(237.1)					(212.0)
Preferred stock - at required rates					(34.9)
Performance shares					(0.7)
Treasury shares acquired						$ (4.3)
Treasury shares acquired (in shares)						(149,544)
Treasury shares reissued						$ 4.1
Treasury shares reissued (in shares)						140,042
Derivative hedging activity, net of tax	4.9						4.9	4.6			4.6
Change in unrecognized pension expense, net of tax	(0.5)						(0.5)
Ending balance at Dec. 31, 2017	$ 4,964.8	$ 4,233.1	$ 0.0	$ 0.0	$ 737.9	$ (4.0)	$ (2.2)	$ 2,513.2	$ 1,563.1	$ 949.7	$ 0.4
Ending balance, treasury stock (in shares) at Dec. 31, 2017	(137,589)					(137,589)
Ending balance (in shares) at Dec. 31, 2017		215,801,723	0	0					1

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies [Text Block]

1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Organization

Great Plains Energy, a Missouri corporation incorporated in 2001, is a public utility holding company and does not own or operate any significant assets other than the stock of its subsidiaries and cash and cash equivalents. Great Plains Energy's wholly owned direct subsidiaries with significant operations are as follows:


•	KCP&L is an integrated, regulated electric utility that provides electricity to customers primarily in the states of Missouri and Kansas. KCP&L has one active wholly owned subsidiary, Kansas City Power & Light Receivables Company (KCP&L Receivables Company).

•

KCP&L Greater Missouri Operations Company (GMO) is an integrated, regulated electric utility that provides electricity to customers in the state of Missouri. GMO also provides regulated steam service to certain customers in the St. Joseph, Missouri area. GMO has two active wholly owned subsidiaries, GMO Receivables Company and MPS Merchant Services, Inc. (MPS Merchant). MPS Merchant has certain long-term natural gas contracts remaining from its former non-regulated trading operations.

Great Plains Energy also wholly owns GPE Transmission Holding Company, LLC (GPETHC). GPETHC owns 13.5% of Transource Energy, LLC (Transource) with the remaining 86.5% owned by AEP Transmission Holding Company, LLC (AEPTHC), a subsidiary of American Electric Power Company, Inc. GPETHC accounts for its investment in Transource under the equity method. Transource is focused on the development of competitive electric transmission projects.

Each of Great Plains Energy's and KCP&L's consolidated financial statements includes the accounts of their subsidiaries. Intercompany transactions have been eliminated.

Great Plains Energy's sole reportable business segment is the electric utility segment (Electric Utility). See Note 22 for additional information.

Use of Estimates

The process of preparing financial statements in conformity with Generally Accepted Accounting Principles (GAAP) requires the use of estimates and assumptions that affect the reported amounts of certain types of assets, liabilities, revenues and expenses. Such estimates primarily relate to unsettled transactions and events as of the date of the financial statements. Accordingly, upon settlement, actual results may differ from estimated amounts.

Cash and Cash Equivalents

Cash equivalents consist of highly liquid investments with original maturities of three months or less at acquisition.

Time Deposit

Consists of a non-negotiable fixed rate investment in a time deposit with an original maturity of greater than three months and is recorded on the balance sheet at cost. The Company estimates the fair value of the time deposit, which approximates its carrying value, using Level 2 inputs based on current interest rates for similar investments with comparable credit risk and time to maturity.

Fair Value of Financial Instruments

The following methods and assumptions were used to estimate the fair value of each class of financial instrument for which it is practicable to estimate that value.

Nuclear decommissioning trust fund - KCP&L's nuclear decommissioning trust fund assets are recorded at fair value based on quoted market prices of the investments held by the fund and/or valuation models.

Pension plans - For financial reporting purposes, the market value of plan assets is the fair value. For regulatory reporting purposes, a five-year smoothing of assets is used to determine fair value.

Derivative Instruments

The Company records derivative instruments on the balance sheet at fair value in accordance with GAAP. Great Plains Energy and KCP&L enter into derivative contracts to manage exposure to commodity price and interest rate fluctuations. Derivative instruments are entered into solely for hedging purposes and are not issued or held for speculative reasons.

The Company considers various qualitative factors, such as contract and market place attributes, in designating derivative instruments at inception. Great Plains Energy and KCP&L may elect the normal purchases and normal sales (NPNS) exception, which requires the effects of the derivative to be recorded when the underlying contract settles. Great Plains Energy and KCP&L account for derivative instruments that are not designated as NPNS as non-hedging derivatives, which are recorded as assets or liabilities on the consolidated balance sheets at fair value.

Great Plains Energy and KCP&L offset fair value amounts recognized for derivative instruments under master netting arrangements, which include rights to reclaim cash collateral (a receivable), or the obligation to return cash collateral (a payable).

Utility Plant

Great Plains Energy's and KCP&L's utility plant is stated at historical cost. These costs include taxes, an allowance for the cost of borrowed and equity funds used to finance construction and payroll-related costs, including pensions and other fringe benefits. Replacements, improvements and additions to units of property are capitalized. Repairs of property and replacements of items not considered to be units of property are expensed as incurred (except as discussed under Deferred Refueling Outage Costs). When property units are retired or otherwise disposed, the original cost, net of salvage, is charged to accumulated depreciation. Substantially all of KCP&L's utility plant is pledged as collateral for KCP&L's mortgage bonds under the General Mortgage Indenture and Deed of Trust dated December 1, 1986, as supplemented (Indenture). A portion of GMO's utility plant is pledged as collateral for GMO's mortgage bonds under the General Mortgage Indenture and Deed of Trust dated April 1, 1946, as supplemented.

As prescribed by The Federal Energy Regulatory Commission (FERC), Allowance for Funds Used During Construction (AFUDC) is charged to the cost of the plant during construction. AFUDC equity funds are included as a non-cash item in non-operating income and AFUDC borrowed funds are a reduction of interest charges. The rates used to compute gross AFUDC are compounded semi-annually. The rates used to compute gross AFUDC for KCP&L averaged 4.9% in 2017, 5.7% in 2016 and 3.0% in 2015. The rates used to compute gross AFUDC for GMO averaged 1.9% in 2017, 1.6% in 2016 and 4.2% in 2015.

Great Plains Energy's and KCP&L's balances of utility plant, at original cost, with a range of estimated useful lives are listed in the following tables.



Great Plains Energy
December 31	2017		2016
Utility plant, at original cost	(millions)
Generation (20 - 60 years)	$	7,930.8	$	8,106.4
Transmission (15 - 70 years)	912.3		886.3
Distribution (8 - 66 years)	3,789.0		3,629.1
General (5 - 50 years)	1,042.0		975.9
Total ^(a)	$	13,674.1	$	13,597.7

^(a) Includes $265.0 million and $261.2 million at December 31, 2017 and 2016, respectively, of land and other assets that are not depreciated.



KCP&L
December 31	2017		2016
Utility plant, at original cost	(millions)
Generation (20 - 60 years)	$	6,471.5	$	6,350.7
Transmission (15 - 70 years)	500.4		484.1
Distribution (8 - 55 years)	2,389.4		2,298.4
General (5 - 50 years)	851.9		791.9
Total ^(a)	$	10,213.2	$	9,925.1

^(a) Includes $176.0 million and $178.0 million at December 31, 2017 and 2016, respectively, of land and other assets that are not depreciated.

Plant to be Retired, Net

When Great Plains Energy and KCP&L retire utility plant, the original cost, net of salvage, is charged to accumulated depreciation. However, when it becomes probable an asset will be retired significantly in advance of its original expected useful life and in the near term, the cost of the asset and related accumulated depreciation is recognized as a separate asset as a probable abandonment. If the asset is still in service, the net amount is classified as plant to be retired, net on the consolidated balance sheets. If the asset is no longer in service, the net amount is classified in regulatory assets on the consolidated balance sheets.

Great Plains Energy and KCP&L must also assess the probability of full recovery of the remaining net book value of the abandonment. The net book value that may be retained as an asset on the balance sheet for the abandonment is dependent upon amounts that may be recovered through regulated rates, including any return. An impairment charge, if any, would equal the difference between the remaining net book value of the asset and the present value of the future revenues expected from the asset.

In June 2017, Great Plains Energy and KCP&L announced the expected retirement of certain older generating units, including GMO's Sibley No. 3 Unit, over the next several years. As of December 31, 2017, Great Plains Energy has determined that Sibley No. 3 Unit meets the criteria to be considered probable of abandonment and has classified its remaining net book value of $143.6 million within plant to be retired, net on its consolidated balance sheet. The Company is currently allowed a full recovery of and a full return on Sibley No. 3 Unit in rates and has concluded that no impairment is required as of December 31, 2017.

Depreciation and Amortization

Depreciation and amortization of utility plant other than nuclear fuel is computed using the straight-line method over the estimated lives of depreciable property based on rates approved by state regulatory authorities. Annual depreciation rates average approximately 3%. Nuclear fuel is amortized to fuel expense based on the quantity of heat produced during the generation of electricity.

Great Plains Energy's depreciation expense was $330.8 million, $308.8 million and $299.4 million for 2017, 2016 and 2015, respectively. KCP&L's depreciation expense was $228.4 million, $215.4 million and $208.5 million for 2017, 2016 and 2015, respectively.

Nuclear Plant Decommissioning Costs

Nuclear plant decommissioning cost estimates are based on the immediate dismantlement method and include the costs of decontamination, dismantlement and site restoration. Based on these cost estimates, KCP&L contributes to a tax-qualified trust fund to be used to decommission Wolf Creek Generating Station (Wolf Creek). Related liabilities for decommissioning are included on Great Plains Energy's and KCP&L's balance sheets in Asset Retirement Obligations (AROs).

As a result of the authorized regulatory treatment and related regulatory accounting, differences between the decommissioning trust fund asset and the related ARO are recorded as a regulatory asset or liability. See Note 8 for discussion of AROs including those associated with nuclear plant decommissioning costs.

Deferred Refueling Outage Costs

KCP&L uses the deferral method to account for operations and maintenance expenses incurred in support of Wolf Creek's scheduled refueling outages and amortizes them evenly (monthly) over the unit's operating cycle, which is approximately 18 months, until the next scheduled outage. Replacement power costs during an outage are expensed as incurred.

Regulatory Matters

KCP&L and GMO defer items on the balance sheet resulting from the effects of the ratemaking process, which would not be recorded if KCP&L and GMO were not regulated. See Note 6 for additional information concerning regulatory matters.

Revenue Recognition

Great Plains Energy and KCP&L recognize revenues on sales of electricity when the service is provided. Revenues recorded include electric services provided but not yet billed by KCP&L and GMO. Unbilled revenues are recorded for kWh usage in the period following the customers' billing cycle to the end of the month. KCP&L's and GMO's estimate is based on net system kWh usage less actual billed kWhs. KCP&L's and GMO's estimated unbilled kWhs are allocated and priced by regulatory jurisdiction across the rate classes based on actual billing rates.

KCP&L and GMO collect from customers gross receipts taxes levied by state and local governments. These taxes from KCP&L's Missouri customers are recorded gross in operating revenues and general taxes on Great Plains Energy's and KCP&L's statements of comprehensive income. KCP&L's gross receipts taxes collected from Missouri customers were $72.9 million, $70.3 million and $62.0 million in 2017, 2016 and 2015, respectively. These taxes from KCP&L's Kansas customers and GMO's customers are recorded net in operating revenues on Great Plains Energy's and KCP&L's statements of comprehensive income (loss).

Great Plains Energy and KCP&L collect sales taxes from customers and remit to state and local governments. These taxes are presented on a net basis on Great Plains Energy's and KCP&L's statements of comprehensive income (loss).

Great Plains Energy and KCP&L record sale and purchase activity on a net basis in wholesale revenue or purchased power when transacting with Regional Transmission Organization (RTO)/Independent System Operator (ISO) markets.

Allowance for Doubtful Accounts

This reserve represents estimated uncollectible accounts receivable and is based on management's judgment considering historical loss experience and the characteristics of existing accounts. Provisions for losses on receivables are expensed to maintain the allowance at a level considered adequate to cover expected losses. Receivables are charged off against the reserve when they are deemed uncollectible.

Property Gains and Losses

Net gains and losses from the sale of assets and businesses and from asset impairments are recorded in operating expenses.

Asset Impairments

Long-lived assets and finite-lived intangible assets subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If the sum of the undiscounted expected future cash flows from an asset to be held and used is less than the carrying value of the asset, an asset impairment must be recognized in the financial statements. The amount of impairment recognized is the excess of the carrying value of the asset over its fair value.

Goodwill and indefinite lived intangible assets are tested for impairment annually and when an event occurs indicating the possibility that an impairment exists. The annual test must be performed at the same time each year. The goodwill impairment test consists of comparing the fair value of a reporting unit to its carrying amount, including goodwill, to identify potential impairment. In the event that the carrying amount exceeds the fair value of the reporting unit, an impairment loss is recognized for the difference between the carrying amount of the reporting unit and its fair value.

Income Taxes

Income taxes are accounted for using the asset/liability approach. Deferred tax assets and liabilities are determined based on the temporary differences between the financial reporting and tax bases of assets and liabilities, applying enacted statutory tax rates in effect for the year in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance when, in the opinion of management, it is more likely than not that some portion of the deferred tax assets will not be realized.

Great Plains Energy and KCP&L recognize tax benefits based on a “more-likely-than-not” recognition threshold. In addition, Great Plains Energy and KCP&L recognize interest accrued related to unrecognized tax benefits in interest expense and penalties in non-operating expenses.

Great Plains Energy files a consolidated federal income tax return as well as unitary and combined income tax returns in several state jurisdictions with Kansas and Missouri being the most significant. Income taxes for consolidated or combined subsidiaries are allocated to the subsidiaries based on separate company computations of income or loss. KCP&L's income tax provision includes taxes allocated based on its separate company income or loss.

As of December 31, 2017, Great Plains Energy and KCP&L have established a net regulatory liability for the additional future refunds to be made to customers for the over collection of income taxes in rates. Tax credits are recognized in the year generated except for certain KCP&L and GMO investment tax credits that have been deferred and amortized over the remaining service lives of the related properties.

Environmental Matters

Environmental costs are accrued when it is probable a liability has been incurred and the amount of the liability can be reasonably estimated.

Non-Operating Income and Expenses

In 2017, Great Plains Energy's non-operating income included $22.8 million of interest income earned on increased cash and cash equivalents at Great Plains Energy in 2017 related to the proceeds from Great Plains Energy's October 2016 common stock and Series B Preferred Stock offerings and March 2017 issuance of $4.3 billion of senior notes and $14.0 million of mark-to-market gains on deal contingent interest rate swaps.

In 2017, Great Plains Energy's non-operating expenses included $15.0 million due to the write-off of previously deferred offering fees as a result of the termination of the stock purchase agreement for $750 million of Series A Preferred Stock between Great Plains Energy and OCM Credit Portfolio LP (OMERS) in July 2017.

Basic and Diluted Earnings (Loss) per Common Share Calculation

To determine basic earnings (loss) per common share (EPS), preferred stock dividend requirements and redemption premium are deducted from net income (loss) before dividing by the average number of common shares outstanding. To determine diluted EPS, preferred stock dividend requirements and redemption premium are added to earnings available for common shareholders for the periods in which the assumed conversion of Great Plains Energy's 7.00% Series B Mandatory Convertible Preferred Stock (Series B Preferred Stock) has a dilutive effect before dividing by the diluted average number of common shares outstanding. See Note 14 for additional information regarding Series B Preferred Stock. The effect of dilutive securities assumes the issuance of common shares applicable to performance shares and restricted stock calculated using the treasury stock method and the number of common shares that would be issued under an assumed conversion of Series B Preferred Stock using the if-converted method.

The following table reconciles Great Plains Energy's basic and diluted EPS.



	2017			2016		2015
	(millions, except per share amounts)
Income (Loss)
Net income (loss)	$	(106.2	)	$	290.0	$	213.0
Less: preferred stock dividend requirements and redemption premium	37.3			16.5		1.6
Earnings (loss) available for common shareholders	$	(143.5	)	$	273.5	$	211.4
Common Shares Outstanding
Average number of common shares outstanding	215.5			169.4		154.2
Add: effect of dilutive securities	—			0.4		0.6
Diluted average number of common shares outstanding	215.5			169.8		154.8
Basic and Diluted EPS	$	(0.67	)	$	1.61	$	1.37

Anti-dilutive shares excluded from the computation of diluted EPS for 2017 were 226,958 performance shares and 144,989 restricted stock shares. Anti-dilutive shares excluded from the computation of diluted EPS for 2016 were 7,805,460 shares of Series B Preferred Stock assumed to be converted. Anti-dilutive shares excluded from the computation of diluted EPS for 2015 were 900 restricted stock shares.

Dividends Declared

In February 2018, Great Plains Energy's Board of Directors (Great Plains Energy Board) declared a quarterly dividend of $0.275 per share on Great Plains Energy's common stock. The common dividend is payable March 20, 2018, to shareholders of record as of February 27, 2018.

In February 2018, KCP&L's Board of Directors declared a cash dividend payable to Great Plains Energy of $60 million payable on March 19, 2018.

New Accounting Standards

In March 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-09, Compensation-Stock Compensation, which is intended to simplify several areas of accounting for share-based compensation arrangements, including the income tax impact, classification on the statement of cash flows and forfeitures. The Companies adopted ASU No. 2016-09 on January 1, 2017. The cumulative effect from the adoption of ASU No. 2016-09 was insignificant to Great Plains Energy's consolidated financial statements and resulted in a reduction to retained earnings of $0.7 million for KCP&L. The Companies have elected to adopt the cash flow presentation of the excess tax benefits as an operating activity prospectively and no prior periods have been adjusted.

In March 2017, the FASB issued ASU No. 2017-07, Compensation-Retirement Benefits, which requires an employer to disaggregate the service cost component from the other components of net benefit cost. The service cost component is to be reported in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The non-service cost components are to be reported separately from service costs and outside of a subtotal of income from operations. The amendments in this update allow only the service cost component to be eligible for capitalization as part of utility plant. The non-service cost components that are no longer eligible for capitalization as part of utility plant will be recorded as a regulatory asset. The new guidance is to be applied retrospectively for the presentation of service cost and non-service cost components in the income statement and prospectively for the capitalization of the service cost component. The Companies adopted ASU No. 2017-07 on January 1, 2018, and it will not have a material impact on their consolidated financial statements as the impacts of adoption are limited to changes in the classification of non-service cost.

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. In August 2015, the FASB issued ASU No. 2015-14, deferring the effective date of ASU No. 2014-09 one year, from January 1, 2017, to January 1, 2018. The ASU replaced most existing revenue recognition guidance in GAAP when it became effective. The Companies adopted ASU No. 2014-09 on January 1, 2018 using the modified retrospective transition method. The adoption of the standard did not have a material impact on the Companies' amount or timing of revenue recognition. The Companies will include additional disclosures regarding the nature, amount and timing of their revenues from contracts with customers, including disaggregated revenue by customer type, in their first quarter 2018 notes to financial statements.

In February 2016, the FASB issued ASU No. 2016-02, Leases, which requires an entity that is a lessee to record a right-of-use asset and a lease liability for lease payments on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. The new guidance is effective for interim and annual periods beginning after December 15, 2018, and is required to be applied using a modified retrospective approach. Great Plains Energy and KCP&L plan to adopt the new guidance on January 1, 2019. The Companies expect that the new guidance will affect the balance sheet by increasing the assets and liabilities recorded related to operating leases and continue to evaluate the effect that ASU No. 2016-02 will have on their income statement, statement of cash flows and related disclosures.

Anticipated Merger with Westar Energy, Inc.

12 Months Ended

Dec. 31, 2017

Anticipated Merger with Westar Energy, Inc. [Abstract]

Anticipated Buiness Combination Disclosure [Text Block]

2. ANTICIPATED MERGER WITH WESTAR ENERGY, INC.

In May 2016, Great Plains Energy entered into an Agreement and Plan of Merger dated as of May 29, 2016, by and among Great Plains Energy, Westar Energy, Inc. (Westar) and GP Star, Inc. (GP Star) (Original Merger Agreement). Pursuant to the Original Merger Agreement, Great Plains Energy would have acquired Westar for (i) $51.00 in cash and (ii) a number of shares of Great Plains Energy common stock, equal to an exchange ratio for each share of Westar common stock issued and outstanding immediately prior to the effective time of the merger, with Westar becoming a wholly owned subsidiary of Great Plains Energy. The acquisition was subject to various shareholder and regulatory approvals, including from The State Corporation Commission of the State of Kansas (KCC), the Public Service Commission of the State of Missouri (MPSC) and FERC.

In April, 2017, KCC issued an order denying Great Plains Energy's, KCP&L's and Westar's joint application for approval of the acquisition of Westar by Great Plains Energy citing concerns with the purchase price, Great Plains Energy's capital structure, quantifiable and demonstrable customer benefits and staffing levels in Westar's service territory, among other items.

In July 2017, Great Plains Energy entered into an Amended and Restated Agreement and Plan of Merger dated as of July 9, 2017 by and among Great Plains Energy, Westar, Monarch Energy Holding, Inc., a Missouri corporation (Holdco), and King Energy, Inc., a Kansas corporation and wholly owned subsidiary of Holdco (Merger Sub) (Amended Merger Agreement). Pursuant to the Amended Merger Agreement, subject to the satisfaction or waiver of certain conditions, Great Plains Energy will merge with and into Holdco, with Holdco surviving such merger, and Merger Sub will merge with and into Westar, with Westar surviving such merger. Pursuant to the Amended Merger Agreement, at closing each outstanding share of Great Plains Energy's and Westar's common stock will be converted into the right to receive 0.5981 and 1.0, respectively, of validly issued, fully paid and nonassessable shares of common stock, no par value, of Holdco. Following the mergers, Holdco, with a new name that has yet to be established, will be the parent of Great Plains Energy's direct subsidiaries, including KCP&L, and Westar.

The anticipated merger with Westar has been structured as a merger of equals in a tax-free exchange of shares that involves no premium paid or received with respect to either Great Plains Energy or Westar. Following the completion of the anticipated merger, Westar shareholders will own approximately 52.5 percent and Great Plains Energy shareholders will own approximately 47.5 percent of the combined company.

Regulatory and Shareholder Approvals

Great Plains Energy's anticipated merger with Westar was unanimously approved by the Great Plains Energy Board and Westar's Board of Directors (Westar Board). In November 2017, shareholders of Great Plains Energy and Westar approved all proposals necessary for the merger of Great Plains Energy and Westar at each company's respective shareholder meeting. The anticipated merger remains subject to regulatory approvals from KCC, the MPSC, the Nuclear Regulatory Commission (NRC), FERC and The Federal Communications Commission (FCC); as well as other contractual conditions.

KCC Approval

In August 2017, Great Plains Energy, KCP&L and Westar filed a joint application with KCC for approval of the anticipated merger with Westar. An evidentiary hearing is expected to occur in March 2018 and a decision from KCC on the joint application is expected by June 5, 2018.

MPSC Approval

In August 2017, Great Plains Energy, KCP&L, GMO and Westar filed a joint application with the MPSC for approval of the anticipated merger with Westar. In January 2018, Great Plains Energy, KCP&L, GMO and Westar reached a stipulation and agreement with the MPSC staff and certain other intervenors in the case settling all issues in the joint application except for the assignment of bill credit amounts to retail electric customers at KCP&L and GMO. The stipulation and agreement imposes certain conditions on Holdco, KCP&L and GMO in the areas of financing, ratemaking, customer service, corporate social responsibility and also includes other general provisions. The stipulation and agreement with the MPSC staff, among other things, provides that retail rates for KCP&L Missouri and GMO customers will not increase as a result of the merger and that in the event KCP&L's or GMO's credit ratings are downgraded below investment grade as a result of their affiliation with Holdco or any of Holdco's affiliates, KCP&L and GMO will be restricted from paying a dividend unless approved by the MPSC or until their credit ratings are restored to investment grade. The stipulation and agreement must still be approved by the MPSC. An evidentiary hearing in the case is expected to occur in March 2018. While there is not a statutory deadline for an MPSC ruling on the joint application, a decision from the MPSC is expected in the second quarter of 2018.

Other Approvals

In September 2017, Great Plains Energy and Westar filed applications with FERC and the NRC for approval of the merger. In October 2017, the Securities and Exchange Commission (SEC) declared effective a registration statement on Form S-4 of Holdco including a joint proxy statement of Great Plains Energy and Westar that was used in connection with Great Plains Energy's and Westar's special shareholder meetings on November 21, 2017, and the registration of shares of Holdco common stock to be issued to Great Plains Energy's and Westar's shareholders at the closing of the anticipated merger. In November 2017, Great Plains Energy and Westar filed their respective Pre-Merger Notification and Report forms with the Federal Trade Commission (FTC) and the Department of Justice (DOJ) under the Hart-Scott-Rodino (HSR) Act. In December 2017, the FTC granted Great Plains Energy's request for early termination of the waiting period under the HSR Act with respect to the anticipated merger. In February 2018, Great Plains Energy, KCP&L, GMO and Westar filed Transfer of Control applications with FCC.

Termination Fees

The Amended Merger Agreement provides that in connection with a termination of the agreement under specified circumstances relating to a failure to obtain regulatory approvals by July 9, 2018 (which date may be extended to January 9, 2019), a final and nonappealable order enjoining the consummation of the anticipated merger in connection with regulatory approvals or failure by Great Plains Energy to comply with its obligations under the Amended Merger Agreement to consummate the closing of the anticipated merger once all of the conditions have been satisfied, Great Plains Energy may be required to pay Westar a termination fee of $190 million. In addition, in the event that the Amended Merger Agreement is terminated by Westar under certain circumstances to enter into a definitive acquisition agreement with respect to a superior proposal, Westar may be required to pay Great Plains Energy a termination fee of $190 million. Similarly, in the event that the Amended Merger Agreement is terminated by Great Plains Energy under certain circumstances to enter into a definitive acquisition agreement with respect to a superior proposal, Great Plains Energy may be required to pay Westar a termination fee of $190 million.

Shareholder Lawsuits

Following the announcement of the Original Merger Agreement in May 2016, two putative class action complaints (which were consolidated and superseded by a consolidated complaint) were filed in the District Court of Shawnee County, Kansas. On October 20, 2017, the lead plaintiff in that consolidated putative class action filed an amended class action petition. The amended petition named as defendants Westar, the Westar Board, Great Plains Energy, Holdco and Merger Sub. The amended petition challenged the proposed merger and alleged breaches of fiduciary duties against the Westar Board in connection with the proposed merger, including the duty of candor, and that Westar, Great Plains Energy, Holdco and Merger Sub aided and abetted such breaches of fiduciary duties.

On September 21, 2017, a putative class action lawsuit was filed in the U.S. District Court for the District of Kansas. The federal class action complaint named as defendants Westar, the Westar Board, Great Plains Energy, Holdco and Merger Sub. The complaint challenged the merger and alleged violations of section 14(a) of the Securities Exchange Act of 1934, as amended (“Exchange Act”) against all of the defendants and violations of section 20(a) of the Exchange Act against the Westar Board.

On October 6, 2017, a putative class action lawsuit was filed in the U.S. District Court for the District of Kansas. The federal class action complaint named as defendants Westar, the Westar Board, Great Plains Energy, Holdco and Merger Sub. The complaint challenged the proposed merger and alleged violations of section 14(a) of the Exchange Act against Westar and the Westar Board and violations of section 20(a) of the Exchange Act against the Westar Board, Great Plains Energy, Holdco and Merger Sub.

On October 13, 2017, a putative class action lawsuit was filed in the U.S. District Court for the Western District of Missouri, Western Division. The federal class action complaint named as defendants Great Plains Energy and the Great Plains Energy Board. The complaint challenged the proposed merger and alleged violations of section 14(a) of the Exchange Act against all of the defendants and violations of section 20(a) of the Exchange Act against the Great Plains Energy Board.

On October 18, 2017, a putative derivative complaint was filed in Shawnee County, Kansas. This putative derivative action named as defendants the Westar Board, Great Plains Energy, Holdco and Merger Sub, with Westar named as a nominal defendant. The complaint challenged the proposed merger and alleged that the Westar Board determined to forego a $380 million break-up fee allegedly payable to Westar associated with the Original Merger Agreement, breached their fiduciary duties to Westar shareholders in connection with the proposed merger, and that Great Plains Energy, Holdco and Merger Sub aided and abetted such breaches of fiduciary duties.

On November 16, 2017, the plaintiffs in these lawsuits agreed in principle to dismiss the lawsuits and, in exchange, Great Plains Energy, Westar Energy and Holdco agreed, solely in order to avoid the risk that litigation might delay or otherwise adversely affect the consummation of the proposed merger under the Amended Merger Agreement and to minimize the expense of defending such actions, to make supplemental disclosures to the Joint Proxy Statement/Prospectus, which were made on Forms 8-K dated November 16, 2017. The lawsuits have been dismissed. These dismissals do not release or otherwise prejudice any potential claims of any member of the putative class, other than for the plaintiffs in these lawsuits, and do not constitute any admission by any of the defendants as to the merits of any claims.

Redemption of Acquisition Financing

In order to fund the cash portion of the acquisition under the Original Merger Agreement, Great Plains Energy completed registered public offerings of 60.5 million shares of common stock for total net proceeds of $1.55 billion and 17.3 million depositary shares each representing a 1/20th interest in a share of Series B Preferred Stock for total net proceeds of $836.2 million in October 2016 and issued, at a discount, $4.3 billion of senior notes in March 2017. Great Plains Energy also entered into a stock purchase agreement with OMERS, pursuant to which Great Plains Energy would issue and sell to OMERS 750,000 shares of preferred stock of Great Plains Energy designated as 7.25% Mandatory Convertible Preferred Stock, Series A (Series A Preferred Stock), without par value, for an aggregate purchase price equal to $750 million at the closing of the acquisition.

In addition to the financings discussed above, Great Plains Energy also entered into a senior unsecured bridge term loan facility in connection with the Original Merger Agreement in an aggregate principal amount of $8.017 billion (which was subsequently reduced to $864.5 million as a result of the completed financings noted above) to support the anticipated transaction and provide flexibility for the timing of long-term financing.

As a result of the Amended Merger Agreement, the following occurred with regards to Great Plains Energy's acquisition financing arrangements:


•	In July 2017, Great Plains Energy redeemed its $4.3 billion of senior notes at a redemption price of 101% of the aggregate principle amount, plus accrued and unpaid interest. See Note 12 for additional information;


•	In August 2017, Great Plains Energy redeemed its Series B Preferred Stock at a redemption price that was equal to a make-whole formula set forth in the terms of the Series B Preferred Stock. See Note 14 for additional information;


•	In July 2017, Great Plains Energy and OMERS terminated their stock purchase agreement for $750 million of Series A Preferred Stock. As a result of this termination, Great Plains Energy recorded $15 million of previously deferred offering fees to non-operating expenses in the third quarter of 2017; and


•	In July 2017, Great Plains Energy terminated its $864.5 million unsecured bridge term loan facility.

Under the Amended Merger Agreement, Great Plains Energy is required to have not less than $1.25 billion in cash and cash equivalents on its balance sheet at the closing of the anticipated merger with Westar. It is expected that this excess cash will be returned to shareholders of the combined company through the repurchase of common stock over time after the closing of the anticipated merger.

Supplemental Cash Flow Information

12 Months Ended

Dec. 31, 2017

Supplemental Cash Flow Elements [Abstract]

Cash Flow, Supplemental Disclosures [Text Block]

3. SUPPLEMENTAL CASH FLOW INFORMATION



Great Plains Energy Other Operating Activities
Year Ended December 31	2017			2016			2015
Cash flows affected by changes in:	(millions)
Receivables	$	14.8		$	(18.3	)	$	12.5
Accounts receivable pledged as collateral	(7.6		)	2.6			(4.0		)
Fuel inventories	5.6			9.6			(28.3		)
Materials and supplies	(9.0		)	(6.5		)	(3.0		)
Accounts payable	9.0			(25.4		)	(11.4		)
Accrued taxes	1.5			8.1			1.1
Accrued interest	(8.0		)	6.1			3.4
Deferred refueling outage costs	15.5			(3.1		)	(6.7		)
Pension and post-retirement benefit obligations	26.1			27.4			18.5
Allowance for equity funds used during construction	(6.0		)	(6.6		)	(4.8		)
Fuel recovery mechanisms	(11.4		)	(46.9		)	47.5
ARO settlements	(28.5		)	(17.4		)	(4.1		)
Other	20.6			28.1			(7.8		)
Total other operating activities	$	22.6		$	(42.3	)	$	12.9
Cash paid during the period:
Interest	$	258.9		$	191.2		$	182.2
Income taxes	$	—		$	0.1		$	0.1
Non-cash investing activities:
Liabilities accrued for capital expenditures	$	39.8		$	32.4		$	35.7



KCP&L Other Operating Activities
Year Ended December 31	2017			2016			2015
Cash flows affected by changes in:	(millions)
Receivables	$	13.8		$	(12.4	)	$	2.6
Accounts receivable pledged as collateral	(20.0		)	—			—
Fuel inventories	1.9			10.6			(24.7		)
Materials and supplies	(7.1		)	(4.3		)	(4.5		)
Accounts payable	11.7			(30.5		)	(18.0		)
Accrued taxes	9.1			67.9			(19.0		)
Accrued interest	—			—			3.4
Deferred refueling outage costs	15.5			(3.1		)	(6.7		)
Pension and post-retirement benefit obligations	27.3			28.6			18.4
Allowance for equity funds used during construction	(6.0		)	(6.6		)	(3.8		)
Fuel recovery mechanisms	8.3			(53.7		)	3.5
ARO settlements	(25.5		)	(15.0		)	(4.1		)
Other	(9.0		)	16.4			(8.6		)
Total other operating activities	$	20.0		$	(2.1	)	$	(61.5	)
Cash paid during the period:
Interest	$	128.0		$	127.0		$	120.2
Income taxes	$	38.8		$	—		$	—
Non-cash investing activities:
Liabilities accrued for capital expenditures	$	32.9		$	27.2		$	23.9

Receivables

12 Months Ended

Dec. 31, 2017

Receivables [Abstract]

Loans Notes Trade And Other Receivables Disclosure And Transfers And Servicing Of Financial Asset [Text Block]

4. RECEIVABLES

Great Plains Energy's and KCP&L's receivables are detailed in the following table.



	December 31
		2017			2016
Great Plains Energy		(millions)
Customer accounts receivable - billed		$	3.7		$	26.2
Customer accounts receivable - unbilled		103.2			79.1
Allowance for doubtful accounts - customer accounts receivable		(4.7		)	(4.0		)
Other receivables		49.5			64.7
Total		$	151.7		$	166.0
KCP&L
Customer accounts receivable - billed		$	1.6		$	25.5
Customer accounts receivable - unbilled		67.6			63.7
Allowance for doubtful accounts - customer accounts receivable		(2.2		)	(1.8		)
Other receivables		39.3			51.7
Total		$	106.3		$	139.1

Great Plains Energy's and KCP&L's other receivables at December 31, 2017 and 2016, consisted primarily of receivables from partners in jointly owned electric utility plants and wholesale sales receivables.

Sale of Accounts Receivable – KCP&L and GMO

KCP&L and GMO sell all of their retail electric accounts receivable to their wholly owned subsidiaries, KCP&L Receivables Company and GMO Receivables Company, respectively, which in turn sell an undivided percentage ownership interest in the accounts receivable to Victory Receivables Corporation, an independent outside investor. Each of KCP&L Receivables Company's and GMO Receivables Company's sale of the undivided percentage ownership interest in accounts receivable to Victory Receivables Corporation is accounted for as a secured borrowing with accounts receivable pledged as collateral and a corresponding short-term collateralized note payable recognized on the balance sheets. At December 31, 2017 and 2016, Great Plains Energy's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $180.0 million and $172.4 million, respectively. At December 31, 2017 and 2016, KCP&L's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $130.0 million and $110.0 million, respectively. In September 2017, KCP&L and GMO amended their respective receivable sale agreements with Victory Receivables Corporation to extend the termination date to September 2018 and to allow for $130 million in aggregate outstanding principal amount of borrowings at any time for KCP&L and $50 million in aggregate outstanding principal amount of borrowings from mid-November through mid-June and then $65 million from mid-June through mid-November for GMO.

Nuclear Plant

12 Months Ended

Dec. 31, 2017

Nuclear Plant [Abstract]

Nuclear Plant

5. NUCLEAR PLANT

KCP&L owns 47% of Wolf Creek, its only nuclear generating unit. Wolf Creek is located in Coffey County, Kansas, just northeast of Burlington, Kansas. Wolf Creek's operating license expires in 2045. Wolf Creek is regulated by the NRC with respect to licensing, operations and safety-related requirements.

Spent Nuclear Fuel and High-Level Radioactive Waste

Under the Nuclear Waste Policy Act of 1982, the Department of Energy (DOE) is responsible for the permanent disposal of spent nuclear fuel. Wolf Creek historically paid the DOE a quarterly fee of one-tenth of a cent for each kWh of net nuclear generation delivered and sold for the future disposal of spent nuclear fuel. In May 2014, this fee was set to zero.

In 2010, the DOE filed a motion with the NRC to withdraw its then pending application to the NRC to construct a national repository for the disposal of spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. An NRC board denied the DOE's motion to withdraw its application. In 2011, the NRC announced that it was evenly divided on whether to take affirmative action to overturn or uphold the board's decision and ordered the licensing board, consistent with budgetary limitations, to close out its work on the DOE's application. In August 2013, a federal court of appeals ruled that the NRC must resume its review of the DOE's application to the extent of appropriated funds. With the available funds, the NRC was able to complete its technical review of the Yucca Mountain application but was not able to resume the licensing hearing.

Wolf Creek is currently evaluating alternatives for expanding its existing on-site spent nuclear fuel storage to provide additional capacity prior to 2025. Management cannot predict when, or if, an off-site storage site or alternative disposal site will be available to receive Wolf Creek's spent nuclear fuel and will continue to monitor this activity.

Low-Level Radioactive Waste

Wolf Creek disposes of most of its low-level radioactive waste (Class A waste) at an existing third-party repository in Utah. Management expects that the site located in Utah will remain available to Wolf Creek for disposal of its Class A waste. Wolf Creek has contracted with a waste processor that will process, take title and dispose in another state most of the remainder of Wolf Creek's low-level radioactive waste (Classes B and C waste, which is higher in radioactivity but much lower in volume). Should on-site waste storage be needed in the future, Wolf Creek has current storage capacity on site for about four years' generation of Classes B and C waste and believes it will be able to expand that storage capacity as needed if it becomes necessary to do so.

Nuclear Plant Decommissioning Costs

The MPSC and KCC require KCP&L and the other owners of Wolf Creek to submit an updated decommissioning cost study every three years and to propose funding levels. The most recent study was submitted to the MPSC and KCC in September 2017 and is the basis for the current cost of decommissioning estimates in the following table. Funding levels included in KCP&L retail rates have not changed. The actual nuclear decommissioning costs may vary from these estimates because of changes in regulations and technologies as well as changes in costs for labor, materials and equipment.



		KCC			MPSC
	(millions)
Current cost of decommissioning (in 2017 dollars)
Total Station		$	813.7		$	813.7
KCP&L's 47% Share		382.5			382.5

Future cost of decommissioning (in 2045-2053 dollars) ^(a)
Total Station		$	1,982.4		$	2,137.8
KCP&L's 47% Share		931.7			1,004.8

Annual escalation factor		2.91		%	3.16		%
Annual return on trust assets ^(b)		5.64		%	5.46		%

^(a)Total future cost over an eight year decommissioning period

^(b)The 5.64% KCC rate of return is through 2029 and then systematically decreases through 2053 to 0.32%. The 5.46% MPSC rate of return is through 2027 and then systematically decreases through 2053 to 2.22%. The KCC and MPSC rates of return systematically decrease based on the assumption that the fund's investment mix will become increasingly conservative as the decommissioning period approaches.

Nuclear Decommissioning Trust Fund

In 2017 and 2016, KCP&L contributed approximately $3.3 million to a tax-qualified trust fund to be used to decommission Wolf Creek. Amounts funded are charged to other operating expense and recovered in customers' rates. The funding level assumes a projected level of return on trust assets. If the actual return on trust assets is below the projected level or actual decommissioning costs are higher than estimated, KCP&L could be responsible for the balance of funds required; however, while there can be no assurances, management believes a rate increase would be allowed to recover decommissioning costs over the remaining life of the unit.

The following table summarizes the change in Great Plains Energy's and KCP&L's nuclear decommissioning trust fund.



	2017			2016
Decommissioning Trust		(millions)
Beginning balance January 1		$	222.9		$	200.7
Contributions		3.3			3.3
Earned income, net of fees		4.3			4.1
Net realized gains		0.7			0.3
Net unrealized gains		27.2			14.5
Ending balance December 31		$	258.4		$	222.9

The nuclear decommissioning trust is reported at fair value on the balance sheets and is invested in assets as detailed in the following table.



	December 31
	2017												2016
	Cost Basis		Unrealized Gains			Unrealized Losses				Fair Value			Cost Basis			Unrealized Gains			Unrealized Losses				Fair Value
	(millions)
Equity securities	$	96.5		$	88.3		$	(1.0	)		$	183.8		$	93.3		$	62.1		$	(1.5	)		$	153.9
Debt securities	69.7			2.7			(0.4		)		72.0			63.4			2.3			(0.5		)		65.2
Other	2.6			—			—				2.6			3.8			—			—				3.8
Total	$	168.8		$	91.0		$	(1.4	)		$	258.4		$	160.5		$	64.4		$	(2.0	)		$	222.9

The weighted average maturity of debt securities held by the trust at December 31, 2017, was approximately 9 years. The costs of securities sold are determined on the basis of specific identification. The following table summarizes the realized gains and losses from the sale of securities in the nuclear decommissioning trust fund.



	2017			2016			2015
	(millions)
Realized gains	$	2.5		$	1.6		$	5.3
Realized losses	(1.8		)	(1.3		)	(4.6		)

Nuclear Insurance

The owners of Wolf Creek (Owners) maintain nuclear insurance for Wolf Creek for nuclear liability, nuclear property and accidental outage. These policies contain certain industry standard exclusions, including, but not limited to, ordinary wear and tear, and war. The nuclear property insurance programs subscribed to by members of the nuclear power generating industry include industry aggregate limits for acts of terrorism and related losses, including replacement power costs. There is no industry aggregate limit for liability claims related to terrorism, regardless of the number of acts of terrorism affecting Wolf Creek or any other nuclear energy liability policy or the number of policies in place. An industry aggregate limit of $3.2 billion plus any reinsurance recoverable by Nuclear Electric Insurance Limited (NEIL), the Owners' insurance provider, exists for property claims related to nuclear acts of terrorism, including accidental outage power costs for nuclear acts of terrorism affecting Wolf Creek or any other nuclear energy facility property policy within twelve months from the date of the first act. An industry aggregate limit of $1.8 billion exists for property claims related to non-nuclear acts of terrorism. These limits plus any recoverable reinsurance are the maximum amount to be paid to members who sustain losses or damages from these types of terrorist acts. In addition, industry-wide retrospective assessment programs (discussed below) can apply once these insurance programs have been exhausted.

In the event of a catastrophic loss at Wolf Creek, the insurance coverage may not be adequate to cover property damage and extra expenses incurred. Uninsured losses, to the extent not recovered through rates, would be assumed by KCP&L and the other owners and could have a material effect on Great Plains Energy's and KCP&L's results of operations, financial position and cash flows.

Nuclear Liability Insurance

Pursuant to the Price-Anderson Act, which was reauthorized through December 31, 2025, by the Energy Policy Act of 2005, the Owners are required to insure against public liability claims resulting from nuclear incidents to the full limit of public liability, which is currently $13.5 billion. This limit of liability consists of the maximum available commercial insurance of $0.5 billion and the remaining $13.0 billion is provided through an industry-wide retrospective assessment program mandated by law, known as the Secondary Financial Protection (SFP) program. Under the SFP program, the Owners can be assessed up to $127.3 million ($59.8 million, KCP&L's 47% share) per incident at any commercial reactor in the country, payable at no more than $19.0 million ($8.9 million, KCP&L's 47% share) per incident per year. This assessment is subject to an inflation adjustment based on the Consumer Price Index and applicable premium taxes. In addition, the U.S. Congress could impose additional revenue-raising measures to pay claims.

Nuclear Property Insurance

The Owners carry decontamination liability, premature decommissioning liability and property damage insurance from NEIL for Wolf Creek totaling approximately $2.8 billion ($1.3 billion, KCP&L's 47% share). In the event of an accident, insurance proceeds must first be used for reactor stabilization and site decontamination in accordance with a plan mandated by the NRC. KCP&L's share of any remaining proceeds can be used for further decontamination, property damage restoration and premature decommissioning costs. Premature decommissioning coverage applies only if an accident at Wolf Creek exceeds $500 million in property damage and decontamination expenses, and only after trust funds have been exhausted.

Accidental Nuclear Outage Insurance

The Owners also carry additional insurance from NEIL to cover costs of replacement power and other extra expenses incurred in the event of a prolonged outage resulting from accidental property damage at Wolf Creek.

Under all NEIL policies, the Owners are subject to retrospective assessments if NEIL losses, for each policy year, exceed the accumulated funds available to the insurer under that policy. The estimated maximum amount of retrospective assessments under the current policies could total approximately $37.4 million ($17.6 million, KCP&L's 47% share) per policy year.

Regulatory Matters

12 Months Ended

Dec. 31, 2017

Regulated Operations [Abstract]

Regulatory Matters

6. REGULATORY MATTERS

KCP&L Missouri 2018 Rate Case Proceedings

In January 2018, KCP&L filed an application with the MPSC to request an increase to its retail revenues of $8.9 million before rebasing fuel and purchased power expense, with a return on equity of 9.85% and a rate-making equity ratio of 50.03%. The request reflects the impact of the Tax Cut and Jobs Act and increases in infrastructure investment costs, transmission related costs and property tax costs. KCP&L also requested an additional $7.5 million increase associated with rebasing fuel and purchased power expense.

GMO Missouri 2018 Rate Case Proceedings

In January 2018, GMO filed an application with the MPSC to request a decrease to its retail revenues of $2.4 million before rebasing fuel and purchased power expense, with a return on equity of 9.85% and a rate-making equity ratio of 54.4%. The request reflects the impact of the Tax Cut and Jobs Act and increases in infrastructure investment costs and transmission related costs. GMO also requested a $21.7 million increase associated with rebasing fuel and purchased power expense.

KCP&L Kansas 2016 Abbreviated Rate Case Proceedings

In November 2016, KCP&L filed an abbreviated application with KCC to request a decrease to its retail revenues of $2.8 million, reflecting the true-up to actuals of construction and environmental upgrade costs at the La Cygne Station and Wolf Creek capital addition costs and the removal of certain regulatory asset and liability amortizations. The previously approved return on equity and rate-making ratio for KCP&L was not addressed in this case. In April 2017, KCP&L, KCC staff and the Citizens' Utility Ratepayer Board filed a joint motion to approve a unanimous settlement agreement with KCC that requested a decrease in retail revenues of $3.6 million. In June 2017, KCC issued an order approving the unanimous settlement agreement. The rates established by the order took effect on June 28, 2017.

KCP&L Missouri 2016 Rate Case Proceedings

In July 2016, KCP&L filed an application with the MPSC to request an increase to its retail revenues of $62.9 million before rebasing fuel and purchased power expense, with a return on equity of 9.9% and a rate-making equity ratio of 49.88%. The request reflects increases in infrastructure investment costs, costs for regional transmission lines, property tax costs and costs to comply with environmental and cybersecurity mandates. KCP&L also requested an additional $27.2 million increase associated with rebasing fuel and purchased power expense.

In May 2017, the MPSC issued an order for KCP&L authorizing an increase in retail revenues of $5.4 million before rebasing fuel and purchased power expense, a return on equity of 9.5% and a rate-making equity ratio of approximately 49.2%. The order also authorized a $27.1 million revenue increase associated with rebasing fuel and purchased power expense. The rates established by the order took effect on June 8, 2017.

Regulatory Assets and Liabilities

Great Plains Energy and KCP&L have recorded assets and liabilities on their consolidated balance sheets resulting from the effects of the ratemaking process, which would not otherwise be recorded if the Companies were not regulated. Regulatory assets represent incurred costs that are probable of recovery from future revenues. Regulatory liabilities represent future reductions in revenues or refunds to customers.

Management regularly assesses whether regulatory assets and liabilities are probable of future recovery or refund by considering factors such as decisions by the MPSC, KCC or FERC in KCP&L's and GMO's rate case filings; decisions in other regulatory proceedings, including decisions related to other companies that establish precedent on matters applicable to the Companies; and changes in laws and regulations. If recovery or refund of regulatory assets or liabilities is not approved by regulators or is no longer deemed probable, these regulatory assets or liabilities are recognized in the current period results of operations. The Companies' continued ability to meet the criteria for recording regulatory assets and liabilities may be affected in the future by restructuring and deregulation in the electric industry or changes in accounting rules. In the event that the criteria no longer applied to any or all of the Companies' operations, the related regulatory assets and liabilities would be written off unless an appropriate regulatory recovery mechanism were provided. Additionally, these factors could result in an impairment on utility plant assets.

Great Plains Energy's and KCP&L's regulatory assets and liabilities are detailed in the following table.



	December 31
	2017								2016
	KCP&L			GMO			Great Plains Energy		KCP&L		GMO		Great Plains Energy
Regulatory Assets	(millions)
Taxes recoverable through future rates	$	—		$	—		$	—	$	123.9	$	24.8	$	148.7
Loss on reacquired debt	8.7		^(a)	1.2		^(a)	9.9		10.0		1.7		11.7
Cost of removal	30.3			—			30.3		28.6		—		28.6
Asset retirement obligations	94.3			24.2			118.5		69.6		24.9		94.5
Pension and post-retirement costs	379.7		^(b)	108.2		^(b)	487.9		367.9		104.7		472.6
Deferred customer programs	40.9		^(c)	19.4		^(d)	60.3		45.9		27.4		73.3
Fuel recovery mechanism	61.7		^(e)	12.0		^(e)	73.7		69.9		—		69.9
Iatan No. 1 and common facilities depreciation and carrying costs	12.9		^(f)	4.7		^(g)	17.6		13.6		5.0		18.6
Iatan No. 2 construction accounting costs	25.0		^(h)	13.7		^(h)	38.7		26.9		16.1		43.0
Kansas property tax surcharge	6.6		^(e)	—			6.6		3.6		—		3.6
Solar rebates	22.6		⁽ⁱ⁾	37.0		^(e)	59.6		29.2		41.6		70.8
Transmission delivery charge	3.2		^(e)	—			3.2		3.1		—		3.1
La Cygne deferred depreciation	2.7		^(j)	—			2.7		2.8		—		2.8
Other	3.3		^(e)	1.6			4.9		6.8		—		6.8
Total	$	691.9		$	222.0		$	913.9	$	801.8	$	246.2	$	1,048.0
Regulatory Liabilities
Taxes refundable through future rates	$	574.0		$	220.6		$	794.6	$	—	$	—	$	—
Emission allowances	58.1			—			58.1		62.1		—		62.1
Asset retirement obligations	126.0			—			126.0		99.7		—		99.7
Cost of removal	—			57.4			57.4		—		65.1		65.1
Fuel recovery mechanism	—			3.9			3.9		—		11.6		11.6
Pension and post-retirement costs	12.0			8.2			20.2		15.3		7.4		22.7
Other	9.1			37.0			46.1		10.3		38.4		48.7
Total	$	779.2		$	327.1		$	1,106.3	$	187.4	$	122.5	$	309.9

^(a)Amortized over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.

^(b) Represents unrecognized gains and losses, prior service and transition costs that will be recognized in future net periodic pension and post-retirement costs, pension settlements amortized over various periods and financial and regulatory accounting method differences that will be eliminated over the life of the pension plans. Of these amounts, $366.3 million and $61.4 million for KCP&L and GMO, respectively, are not included in rate base and are amortized over various periods.

^(c) $16.1 million not included in rate base and amortized over various periods.

^(d)$10.9 million not included in rate base and amortized over various periods.

^(e)Not included in rate base and amortized over various periods.

^(f)Included in rate base and amortized over various periods.


^(g)	Included in rate base and amortized through 2038.

^(h)Included in rate base and amortized through 2059.

⁽ⁱ⁾Not included in rate base and amortized through 2020.

^(j)Included in rate base and amortized through 2040.

Goodwill and Intangible Assets

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets [Text Block]

7. GOODWILL AND INTANGIBLE ASSETS

Accounting rules require goodwill to be tested for impairment annually and when an event occurs indicating the possibility that an impairment exists. The annual impairment test for the $169.0 million of GMO acquisition goodwill was conducted on September 1, 2017. The goodwill impairment test consists of comparing the fair value of a reporting unit to its carrying amount, including goodwill, to identify potential impairment. In the event that the carrying amount exceeds the fair value of the reporting unit, an impairment loss is recognized for the difference between the carrying amount of the reporting unit and its fair value. Great Plains Energy's regulated electric utility operations are considered one reporting unit for assessment of impairment, as they are included within the same operating segment and have similar economic characteristics. The determination of fair value of the reporting unit consisted of two valuation techniques: an income approach consisting of a discounted cash flow analysis and a market approach consisting of a determination of reporting unit invested capital using market multiples derived from the historical revenue; earnings before interest, income taxes, depreciation and amortization; net utility asset values and market prices of stock of peer companies. The results of the two techniques were evaluated and weighted to determine a point within the range that management considered representative of fair value for the reporting unit. Fair value of the reporting unit exceeded the carrying amount, including goodwill; therefore, there was no impairment of goodwill.

Great Plains Energy's and KCP&L's intangible assets are included in electric utility plant on the consolidated balance sheets and are detailed in the following table.



	December 31
		2017							2016
	Gross Carrying Amount			Accumulated Amortization				Gross Carrying Amount			Accumulated Amortization
Great Plains Energy	(millions)
Computer software		$	386.8		$	(251.2	)		$	355.2		$	(219.1	)
Asset improvements		30.3			(8.0		)		28.8			(6.7		)

KCP&L
Computer software		$	368.7		$	(234.3	)		$	338.3		$	(203.1	)
Asset improvements		15.1			(2.7		)		13.6			(1.8		)

Great Plains Energy's and KCP&L's amortization expense related to intangible assets is detailed in the following table.



	2017		2016
	(millions)
Great Plains Energy	$	33.7	$	29.1
KCP&L	32.1		25.7

The following table provides the estimated amortization expense related to Great Plains Energy's and KCP&L's intangible assets for 2018 through 2022 for the intangible assets included in the consolidated balance sheets at December 31, 2017.



	2018		2019		2020		2021		2022
	(millions)
Great Plains Energy	$	30.5	$	25.7	$	24.5	$	20.0	$	14.9
KCP&L	29.7		25.0		23.8		19.5		14.5

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

Asset Retirement Obligations

12 Months Ended

Dec. 31, 2017

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations [Text Block]

8. ASSET RETIREMENT OBLIGATIONS

AROs associated with tangible long-lived assets are legal obligations that exist under enacted laws, statutes and written or oral contracts, including obligations arising under the doctrine of promissory estoppel. These liabilities are recognized at estimated fair value as incurred with a corresponding amount capitalized as part of the cost of the related long-lived assets and depreciated over their useful lives. Accretion of the liabilities due to the passage of time is recorded to a regulatory asset and/or liability. Changes in the estimated fair values of the liabilities are recognized when known. Great Plains Energy and KCP&L record the current portion of AROs within other current liabilities on their consolidated balance sheets.

KCP&L has AROs related to decommissioning Wolf Creek, site remediation of its Spearville Wind Energy Facilities, asbestos abatement, removal of storage tanks and closure and post-closure of ponds and landfills containing coal combustion residuals (CCRs). GMO has AROs related to asbestos abatement, removal of storage tanks and closure and post-closure of ponds and landfills containing CCRs.

Additionally, certain wiring used in Great Plains Energy's and KCP&L's generating stations include asbestos insulation, which would require special handling if disturbed. Due to the inability to reasonably estimate the quantities or the amount of disturbance that will be necessary during dismantlement at the end of the life of a plant, the fair value of this ARO cannot be reasonably estimated at this time. Management will continue to monitor the obligation and will recognize a liability in the period in which sufficient information becomes available to reasonably estimate its fair value.

On April 17, 2015, the Environmental Protection Agency (EPA) published new regulations to regulate the disposal of CCRs at electric generation facilities. The CCR rule represents legal obligations of Great Plains Energy and KCP&L as to the closure and post-closure of its ponds and landfills containing CCRs. In 2016, Great Plains Energy and KCP&L revised their AROs by $42.1 million and $40.1 million, respectively, due to an increase in cost estimates for the closure of ponds and landfills containing CCRs at KCP&L's electric generating facilities.

The following table summarizes the change in Great Plains Energy's and KCP&L's AROs.



	Great Plains Energy						KCP&L
	2017			2016			2017			2016
	(millions)
Beginning balance	$	316.0		$	275.9		$	278.0		$	239.3
Additions	—			1.6			—			1.3
Revision in timing and/or estimates	(1.3		)	42.1			0.3			40.1
Settlements	(28.5		)	(17.4		)	(25.5		)	(15.0		)
Accretion	14.9			13.8			13.5			12.3
Total	$	301.1		$	316.0		$	266.3		$	278.0
Less: current portion	(38.6		)	—			(34.9		)	—
Total noncurrent asset retirement obligation	$	262.5		$	316.0		$	231.4		$	278.0

ARO settlement activity in 2017 and 2016 primarily consists of the remediation of AROs for the closure of ponds and landfills containing CCRs at KCP&L and GMO.

Pension Plans and Other Employee Benefits

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Pension Plans and Other Employee Benefits

9. PENSION PLANS AND OTHER EMPLOYEE BENEFITS

Great Plains Energy maintains defined benefit pension plans for the majority of KCP&L's and GMO's active and inactive employees, including officers, and its 47% ownership share of Wolf Creek Nuclear Operating Corporation (WCNOC) defined benefit plans. For the majority of employees, pension benefits under these plans reflect the employees' compensation, years of service and age at retirement. Effective in 2014, Great Plains Energy's non-union plan was closed to future employees. Great Plains Energy also provides certain post-retirement health care and life insurance benefits for substantially all retired employees of KCP&L, GMO and its 47% ownership share of WCNOC.

KCP&L and GMO record pension and post-retirement expense in accordance with rate orders from the MPSC and KCC that allow the difference between pension and post-retirement costs under GAAP and costs for ratemaking to be recognized as a regulatory asset or liability. This difference between financial and regulatory accounting methods is due to timing and will be eliminated over the life of the plans.

In 2017, Great Plains Energy incurred pension settlement charges of $15.9 million as a result of accelerated pension distributions.

The following pension benefits tables provide information relating to the funded status of all defined benefit pension plans on an aggregate basis as well as the components of net periodic benefit costs. For financial reporting purposes, the market value of plan assets is the fair value. For regulatory reporting purposes, a five-year smoothing of assets is used to determine fair value. Net periodic benefit costs reflect total plan benefit costs prior to the effects of capitalization and sharing with joint owners of power plants.



	Pension Benefits						Other Benefits
	2017			2016			2017			2016
Change in projected benefit obligation (PBO)	(millions)
PBO at January 1	$	1,244.6		$	1,154.8		$	130.1		$	137.5
Service cost	44.2			42.0			2.1			2.6
Interest cost	53.5			52.9			5.4			6.1
Contribution by participants	—			—			6.0			5.3
Amendments	—			—			—			(10.1		)
Actuarial (gain) loss	135.6			65.5			2.1			0.6
Benefits paid	(36.8		)	(70.6		)	(12.5		)	(11.9		)
Settlements and special termination benefits	(85.2		)	—			—			—
PBO at December 31	$	1,355.9		$	1,244.6		$	133.2		$	130.1
Change in plan assets
Fair value of plan assets at January 1	$	776.8		$	723.9		$	115.6		$	114.3
Actual return on plan assets	114.8			51.1			1.8			2.6
Contributions by employer and participants	76.9			69.8			10.4			10.2
Benefits paid	(34.5		)	(68.0		)	(12.0		)	(11.5		)
Settlements	(85.6		)	—			—			—
Fair value of plan assets at December 31	$	848.4		$	776.8		$	115.8		$	115.6
Funded status at December 31	$	(507.5	)	$	(467.8	)	$	(17.4	)	$	(14.5	)
Amounts recognized in the consolidated balance sheets
Non-current asset	$	—		$	—		$	12.8		$	9.0
Current pension and other post-retirement liability	(1.9		)	(2.2		)	(0.8		)	(0.8		)
Noncurrent pension liability and other post-retirement liability	(505.6		)	(465.6		)	(29.4		)	(22.7		)
Net amount recognized before regulatory treatment	(507.5		)	(467.8		)	(17.4		)	(14.5		)
Accumulated OCI or regulatory asset/liability	492.2			476.9			(21.1		)	(23.6		)
Net amount recognized at December 31	$	(15.3	)	$	9.1		$	(38.5	)	$	(38.1	)
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Actuarial (gain) loss	$	248.9		$	242.5		$	2.8		$	(0.7	)
Prior service cost	2.5			3.2			(8.0		)	(8.0		)
Other	240.8			231.2			(15.9		)	(14.9		)
Net amount recognized at December 31	$	492.2		$	476.9		$	(21.1	)	$	(23.6	)



	Pension Benefits									Other Benefits
	2017			2016			2015			2017			2016			2015
Components of net periodic benefit costs	(millions)
Service cost	$	44.2		$	42.0		$	45.3		$	2.1		$	2.6		$	3.3
Interest cost	53.5			52.9			50.3			5.4			6.1			6.8
Expected return on plan assets	(51.2		)	(49.2		)	(51.7		)	(2.6		)	(3.1		)	(2.9		)
Prior service cost	0.7			0.7			0.8			—			1.2			3.1
Recognized net actuarial (gain) loss	49.7			51.8			51.4			(0.5		)	(1.5		)	0.2
Transition obligation	—			—			—			—			—			0.2
Settlement and special termination benefits	16.3			—			—			—			—			—
Net periodic benefit costs before regulatory adjustment	113.2			98.2			96.1			4.4			5.3			10.7
Regulatory adjustment	(13.8		)	(4.9		)	(9.8		)	1.9			6.0			4.4
Net periodic benefit costs	99.4			93.3			86.3			6.3			11.3			15.1
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Current year net (gain) loss	72.0			63.6			8.6			3.0			1.1			(20.6		)
Amortization of gain (loss)	(65.6		)	(51.8		)	(51.4		)	0.5			1.5			(0.2		)
Prior service cost	—			—			—			—			(10.2		)	(7.0		)
Amortization of prior service cost	(0.7		)	(0.7		)	(0.8		)	—			(1.2		)	(3.1		)
Amortization of transition obligation	—			—			—			—			—			(0.2		)
Other regulatory activity	9.6			4.6			4.3			(1.0		)	(5.4		)	(4.4		)
Total recognized in OCI or regulatory asset/liability	15.3			15.7			(39.3		)	2.5			(14.2		)	(35.5		)
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	$	114.7		$	109.0		$	47.0		$	8.8		$	(2.9	)	$	(20.4	)

For financial reporting purposes, the estimated prior service cost and net loss for the defined benefit plans that will be amortized from accumulated other comprehensive income (OCI) or a regulatory asset into net periodic benefit cost in 2018 are $0.7 million and $45.7 million, respectively. For financial reporting purposes, net actuarial gains and losses are recognized on a rolling five-year average basis. For regulatory reporting purposes, net actuarial gains and losses are amortized over ten years. The estimated net gain for the other post-retirement benefit plans that will be amortized from accumulated OCI or a regulatory asset into net periodic benefit cost in 2018 is $0.2 million.

The accumulated benefit obligation (ABO) for all defined benefit pension plans was $1,169.8 million and $1,090.2 million at December 31, 2017, and 2016, respectively. Pension and other post-retirement benefit plans with the PBO, ABO or accumulated other post-retirement benefit obligation (APBO) in excess of the fair value of plan assets at year-end are detailed in the following table.



	2017		2016
Pension plans with the PBO in excess of plan assets	(millions)
Projected benefit obligation	$	1,355.9	$	1,244.6
Fair value of plan assets	848.4		776.8
Pension plans with the ABO in excess of plan assets
Accumulated benefit obligation	$	1,169.8	$	1,090.2
Fair value of plan assets	848.4		776.8
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated other post-retirement benefit obligation	$	111.6	$	61.7
Fair value of plan assets	81.5		38.3

The GMO Supplemental Executive Retirement Plan (SERP) is reflected as an unfunded ABO of $24.0 million. Great Plains Energy has approximately $14.7 million of assets in a non-qualified trust for this plan as of December 31, 2017, and expects to fund future benefit payments from these assets.

The expected long-term rate of return on plan assets represents Great Plains Energy's estimate of the long-term return on plan assets and is based on historical and projected rates of return for current and planned asset classes in the plans' investment portfolios. Assumed projected rates of return for each asset class were selected after analyzing historical experience and future expectations of the returns of various asset classes. Based on the target asset allocation for each asset class, the overall expected rate of return for the portfolios was developed and adjusted for the effect of projected benefits paid from plan assets and future plan contributions. The following tables provide the weighted-average assumptions used to determine benefit obligations and net costs.



Weighted-average assumptions used to determine the benefit obligation at December 31	Pension Benefits				Other Benefits
	2017		2016		2017		2016
Discount rate	3.72	%	4.31	%	3.64	%	4.20	%
Rate of compensation increase	3.62	%	3.62	%	3.50	%	3.50	%



Weighted-average assumptions used to determine net costs for years ended December 31	Pension Benefits				Other Benefits
	2017		2016		2017			2016
Discount rate	4.31	%	4.54	%	4.20	%		4.47	%
Expected long-term return on plan assets	6.73	%	7.14	%	2.00	%	*	2.54	%	*
Rate of compensation increase	3.62	%	3.62	%	3.50	%		3.50	%

*after tax

Great Plains Energy expects to contribute $84.0 million to the pension plans in 2018 to meet Employee Retirement Income Security Act of 1974, as amended (ERISA) funding requirements and regulatory orders, the majority of which is expected to be paid by KCP&L. Great Plains Energy's funding policy is to contribute amounts sufficient to meet the ERISA funding requirements and MPSC and KCC rate orders plus additional amounts as considered appropriate; therefore, actual contributions may differ from expected contributions. Great Plains Energy also expects to contribute $4.6 million to other post-retirement benefit plans in 2018, the majority of which is expected to be paid by KCP&L.

The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid through 2027.



	Pension Benefits		Other Benefits
	(millions)
2018	$	79.3	$	9.2
2019	82.2		9.2
2020	84.7		9.6
2021	86.0		10.1
2022	86.5		10.4
2023-2027	459.9		55.6

Pension plan assets are managed in accordance with prudent investor guidelines contained in the ERISA requirements. The investment strategy supports the objective of the fund, which is to earn the highest possible return on plan assets within a reasonable and prudent level of risk. The portfolios are invested, and periodically rebalanced, to achieve targeted allocations of approximately 33% U.S. large cap and small cap equity securities, 21% international equity securities, 36% fixed income securities, 7% real estate, 1% commodities and 2% hedge funds. Fixed income securities include domestic and foreign corporate bonds, collateralized mortgage obligations and asset-backed securities, U.S. government agency, state and local obligations, U.S. Treasury notes and money market funds.

The fair values of Great Plains Energy's pension plan assets at December 31, 2017 and 2016, by asset category are in the following tables.



				Fair Value Measurements Using
Description	December 31 2017			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)			Assets measured at NAV
		(millions)
Pension Plans
Equity securities
U.S. ^(a)		$	279.8		$	236.4		$	—		$	—	$	43.4
International ^(b)		176.0			123.5			—			—		52.5
Real estate ^(c)		46.4			13.6			—			—		32.8
Commodities ^(d)		17.0			—			—			—		17.0
Fixed income securities
Fixed income funds ^(e)		71.8			21.4			—			—		50.4
U.S. Treasury		51.5			51.5			—			—		—
U.S. Agency, state and local obligations		18.3			—			18.3			—		—
U.S. corporate bonds ^(f)		119.2			—			119.2			—		—
Foreign corporate bonds		12.5			—			12.5			—		—
Hedge funds ^(g)		15.7			—			—			—		15.7
Cash equivalents		35.6			35.6			—			—		—
Other		4.6			—			4.6			—		—
Total		$	848.4		$	482.0		$	154.6		$	—	$	211.8



					Fair Value Measurements Using
Description	December 31 2016				Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)				Significant Unobservable Inputs (Level 3)			Assets measured at NAV
Pension Plans		(millions)
Equity securities
U.S. ^(a)		$	247.6			$	213.0		$	—			$	—	$	34.6
International ^(b)		163.7				120.4			—				—		43.3
Real estate ^(c)		42.7				12.4			—				—		30.3
Commodities ^(d)		14.1				—			—				—		14.1
Fixed income securities
Fixed income funds ^(e)		65.1				20.9			—				—		44.2
U.S. Treasury		52.2				52.2			—				—		—
U.S. Agency, state and local obligations		17.9				—			17.9				—		—
U.S. corporate bonds ^(f)		120.2				—			120.2				—		—
Foreign corporate bonds		9.3				—			9.3				—		—
Hedge funds ^(g)		15.6				—			—				—		15.6
Cash equivalents		31.7				31.7			—				—		—
Other		(3.3		)		—			(3.3		)		—		—
Total		$	776.8			$	450.6		$	144.1			$	—	$	182.1

^(a) At December 31, 2017 and 2016, this category is comprised of $75.5 million and $128.8 million, respectively, of traded mutual funds valued at daily listed prices and $160.9 million and $84.2 million, respectively, of traded common stocks and exchange traded funds. At December 31, 2017 and 2016, this category also includes $43.4 million and $34.6 million, respectively, of institutional common/collective trust funds valued at net asset value (NAV) per share (or its equivalent) and is not categorized in the fair value hierarchy.

^(b)At December 31, 2017 and 2016, this category is comprised of $95.6 million and $92.8 million, respectively, of traded mutual funds valued at daily listed prices and $27.9 million and $27.6 million, respectively, of traded American depository receipts, global depository receipts and ordinary shares. At December 31, 2017 and 2016, this category also includes $52.5 million and $43.3 million, respectively, of institutional common/collective trust funds valued at NAV per share (or its equivalent) and is not categorized in the fair value hierarchy.

^(c)At December 31, 2017 and 2016, this category is comprised of $13.6 million and $12.4 million, respectively, of traded real estate investment trusts. At December 31, 2017 and 2016, this category also includes $32.8 million and $30.3 million, respectively, of institutional common/collective trust funds and a limited partnership valued at NAV per share (or its equivalent) and is not categorized in the fair value hierarchy.

^(d)Consists of institutional common/collective trust funds valued at NAV per share (or its equivalent) and is not categorized in the fair value hierarchy.

^(e)At December 31, 2017 and 2016, this category is comprised of $21.4 million and $20.9 million, respectively, of traded mutual funds valued at daily listed prices. At December 31, 2017 and 2016, this category also includes $50.4 million and $44.2 million, respectively, of institutional common/collective trust funds valued at NAV per share (or its equivalent) and is not categorized in the fair value hierarchy.

^(f)At December 31, 2017 and 2016, this category is comprised of $113.3 million and $115.7 million, respectively, of corporate bonds. At December 31, 2017 and 2016, there were also $3.2 million and $2.3 million, respectively, of collateralized mortgage obligations and $2.7 million and $2.2 million, respectively, of other asset-backed securities.

^(g)Consists of closely-held limited partnerships valued at NAV per share (or its equivalent) and is not categorized in the fair value hierarchy.

Other post-retirement plan assets are also managed in accordance with prudent investor guidelines contained in the ERISA requirements. The investment strategy supports the objective of the funds, which is to preserve capital, maintain sufficient liquidity and earn a consistent rate of return. Other post-retirement plan assets are invested primarily in fixed income securities, which may include domestic and foreign corporate bonds, collateralized mortgage obligations and asset-backed securities, U.S. government agency, state and local obligations, U.S. Treasury notes and money market funds, as well as domestic and international equity funds.

The fair values of Great Plains Energy's other post-retirement plan assets at December 31, 2017 and 2016, by asset category are in the following tables.



				Fair Value Measurements Using
Description	December 31 2017			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)			Assets measured at NAV
Other Post-Retirement Benefit Plans		(millions)
Equity securities		$	3.7		$	3.7		$	—		$	—	$	—
Fixed income securities
Fixed income fund^(a)		56.4			—			—			—		56.4
U.S. Treasury		3.0			3.0			—			—		—
U.S. Agency, state and local obligations		5.5			—			5.5			—		—
U.S. corporate bonds^(b)		18.7			—			18.7			—		—
Foreign corporate bonds		1.6			—			1.6			—		—
Cash equivalents		25.3			25.3			—			—		—
Mutual funds		0.2			0.2			—			—		—
Other		1.4			—			1.4			—		—
Total		$	115.8		$	32.2		$	27.2		$	—	$	56.4



				Fair Value Measurements Using
Description	December 31 2016			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)			Assets measured at NAV
Other Post-Retirement Benefit Plans		(millions)
Equity securities		$	4.1		$	4.1		$	—		$	—	$	—
Fixed income securities
Fixed income fund^(a)		62.7			—			—			—		62.7
U.S. Treasury		3.9			3.9			—			—		—
U.S. Agency, state and local obligations		4.3			—			4.3			—		—
U.S. corporate bonds^(b)		17.8			—			17.8			—		—
Foreign corporate bonds		1.6			—			1.6			—		—
Cash equivalents		19.5			19.5			—			—		—
Other		1.7			0.2			1.5			—		—
Total		$	115.6		$	27.7		$	25.2		$	—	$	62.7

^(a) At December 31, 2017 and 2016, this category includes $56.4 million and $62.7 million, respectively, of an institutional common/collective trust fund valued at NAV per share (or its equivalent) and is not categorized in the fair value hierarchy.

^(b) At December 31, 2017 and 2016, this category is comprised of $15.1 million and $14.0 million, respectively, of corporate bonds, $0.5 million and $0.5 million, respectively, of collateralized mortgage obligations and $3.1 million and $3.3 million, respectively, of other asset-backed securities.

Assumed health care cost trend rates have a significant effect on the amounts reported for the health care plans. The cost trend assumed for 2017 and 2018 was 6.5% and 6.8%, respectively, with the rate declining through 2027 to the ultimate cost trend rate of 4.5%.

The effects of a one-percentage point change in the assumed health care cost trend rates, holding all other assumptions constant, at December 31, 2017, are detailed in the following table.



	Increase		Decrease
	(millions)
Effect on total service and interest component	$	0.2	$	(0.2	)
Effect on post-retirement benefit obligation	0.4		(0.3		)

Employee Savings Plans

Great Plains Energy has defined contribution savings plans (401(k)) that cover substantially all employees. Great Plains Energy matches employee contributions, subject to limits. The annual cost of the plans was approximately $10.9 million in 2017, $11.5 million in 2016 and $10.6 million in 2015. KCP&L's annual cost of the plans was approximately $7.7 million in 2017, $8.0 million in 2016 and $7.9 million in 2015.

Equity Compensation

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Equity Compensation

10. EQUITY COMPENSATION

Great Plains Energy's Long-Term Incentive Plan is an equity compensation plan approved by Great Plains Energy's shareholders. The Long-Term Incentive Plan permits the grant of restricted stock, restricted stock units, bonus shares, stock options, stock appreciation rights, director shares, director deferred share units, performance shares and other stock-based awards to directors, officers and other employees of Great Plains Energy and KCP&L. The maximum number of shares of Great Plains Energy common stock that can be issued under the plan is 8.0 million. Common stock shares delivered by Great Plains Energy under the Long-Term Incentive Plan may be authorized but unissued, held in the treasury or purchased on the open market (including private purchases) in accordance with applicable securities laws. Great Plains Energy expects to purchase common stock on the open market during 2018 to satisfy performance share payments and director deferred share unit conversion. Forfeiture rates are based on historical forfeitures and future expectations and are reevaluated annually.

The following table summarizes Great Plains Energy's and KCP&L's equity compensation expense and the associated income tax benefit.



	2017		2016		2015
Great Plains Energy	(millions)
Equity compensation expense	$	6.3	$	5.0	$	4.0
Income tax benefit	2.4		1.6		1.4
KCP&L
Equity compensation expense	$	4.2	$	3.2	$	2.6
Income tax benefit	1.6		1.0		0.9

Performance Shares

The payment of performance shares is contingent upon achievement of specific performance goals over a stated period of time as approved by the Compensation and Development Committee of the Board. The number of performance shares ultimately paid can vary from the number of shares initially granted depending on Great Plains Energy's performance over stated performance periods. Compensation expense for performance shares is calculated by recognizing the portion of the fair value for each reporting period for which the requisite service has been rendered. Dividends are accrued over the vesting period and paid in cash based on the number of performance shares ultimately paid.

The fair value of performance share awards is estimated using the market value of the Company's stock at the valuation date and a Monte Carlo simulation technique that incorporates assumptions for inputs of expected volatilities, dividend yield and risk-free rates. Expected volatility is based on daily stock price change during a historical period commensurate with the remaining term of the performance period of the grant. The risk-free rate is based upon the rate at the time of the evaluation for zero-coupon government bonds with a maturity consistent with the remaining performance period of the grant. The dividend yield is based on the most recent dividends paid and the actual closing stock price on the valuation date. For shares granted in 2017, inputs for expected volatility, dividend yield and risk-free rates were 18%, 3.8% and 1.58%, respectively.

Performance share activity is summarized in the following table. Performance adjustment represents the number of shares of common stock related to performance shares ultimately issued that can vary from the number of performance shares initially granted depending on Great Plains Energy's performance over a stated period of time.



	Performance Shares			Grant Date Fair Value*
Beginning balance January 1, 2017		625,100			$	28.13
Granted		236,433			31.26
Earned		(212,992	)		28.48
Forfeited		(103,454	)		29.24
Ending balance December 31, 2017		545,087			29.12

* weighted-average

At December 31, 2017, the remaining weighted-average contractual term was 1.1 years. The weighted-average grant-date fair value of shares granted was $31.26, $31.41 and $24.03 in 2017, 2016 and 2015, respectively. At December 31, 2017, there was $6.1 million of total unrecognized compensation expense, net of forfeiture rates, related to performance shares granted under the Long-Term Incentive Plan, which will be recognized over the remaining weighted-average contractual term. The total fair value of performance shares earned and paid was $6.1 million, $7.4 million and $0.5 million in 2017, 2016 and 2015, respectively.

Restricted Stock

Restricted stock cannot be sold or otherwise transferred by the recipient prior to vesting and has a value equal to the fair market value of the shares on the issue date. Restricted stock shares vest over a stated period of time with accruing reinvested dividends subject to the same restrictions. Compensation expense, calculated by multiplying shares by the grant-date fair value related to restricted stock, is recognized over the stated vesting period. Restricted stock activity is summarized in the following table.



	Nonvested Restricted Stock			Grant Date Fair Value*
Beginning balance January 1, 2017		249,672			$	27.20
Granted and issued		81,040			28.68
Vested		(112,813	)		26.92
Forfeited		(25,497	)		28.10
Ending balance December 31, 2017		192,402			27.87

* weighted-average

At December 31, 2017, the remaining weighted-average contractual term was 1.2 years. The weighted-average grant-date fair value of shares granted was $28.68, $29.41 and $25.89 in 2017, 2016 and 2015, respectively. At December 31, 2017, there was $2.1 million of total unrecognized compensation expense, net of forfeiture rates, related to nonvested restricted stock granted under the Long-Term Incentive Plan, which will be recognized over the remaining weighted-average contractual term. Total fair value of shares vested was $3.0 million, $1.8 million and $2.2 million in 2017, 2016 and 2015, respectively.

Director Deferred Share Units

Non-employee directors receive shares of Great Plains Energy's common stock as part of their annual retainer. Each director may elect to defer receipt of their shares by receiving Director Deferred Share Units that convert to shares of Great Plains Energy's common stock at the end of January in the year after departure from the Board or such other time as elected by each director. Director Deferred Share Units have a value equal to the market value of Great Plains Energy's common stock on the grant date with accruing dividends. Compensation expense, calculated by multiplying the director deferred share units by the related grant-date fair value, is recognized at the grant date. The total fair value of shares of Director Deferred Share Units issued was insignificant for 2017 and 2016. Director Deferred Share Units activity is summarized in the following table.



	Share Units			Grant Date Fair Value*
Beginning balance January 1, 2017		138,587			$	23.96
Issued		23,435			30.09
Converted		(22,871	)		21.81
Ending balance December 31, 2017		139,151			25.35

* weighted-average

Short-term Borrowings and Short-term Bank Lines of Credit	12 Months Ended
	Dec. 31, 2017
Short-term Borrowings and Short-term Bank Lines of Credit [Abstract]
Short-term Borrowings and Short-term Bank Lines of Credit [Text Block]	11. SHORT-TERM BORROWINGS AND SHORT-TERM BANK LINES OF CREDIT Great Plains Energy's $200 Million Revolving Credit Facility Great Plains Energy's $200 million revolving credit facility with a group of banks expires in October 2019. The facility's terms permit transfers of unused commitments between this facility and the KCP&L and GMO facilities discussed below, with the total amount of the facility not exceeding $400 million at any one time. A default by Great Plains Energy or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, Great Plains Energy is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times. At December 31, 2017, Great Plains Energy was in compliance with this covenant. At December 31, 2017, Great Plains Energy had $11.0 million of outstanding cash borrowings at a weighted-average interest rate of 2.94% and had issued $1.0 million in letters of credit under the credit facility. At December 31, 2016, Great Plains Energy had no outstanding cash borrowings and had issued $1.0 million in letters of credit under the credit facility. KCP&L's $600 Million Revolving Credit Facility and Commercial Paper KCP&L's $600 million revolving credit facility with a group of banks provides support for its issuance of commercial paper and other general corporate purposes and expires in October 2019. Great Plains Energy and KCP&L may transfer up to $200 million of unused commitments between Great Plains Energy's and KCP&L's facilities. A default by KCP&L on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, KCP&L is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times. At December 31, 2017, KCP&L was in compliance with this covenant. At December 31, 2017, KCP&L had $167.5 million of commercial paper outstanding at a weighted-average interest rate of 1.95%, had issued letters of credit totaling $2.7 million and had no outstanding cash borrowings under the credit facility. At December 31, 2016, KCP&L had $132.9 million of commercial paper outstanding at a weighted-average interest rate of 0.98%, had issued letters of credit totaling $2.8 million and had no outstanding cash borrowings under the credit facility. GMO's $450 Million Revolving Credit Facility and Commercial Paper GMO's $450 million revolving credit facility with a group of banks provides support for its issuance of commercial paper and other general corporate purposes and expires in October 2019. Great Plains Energy and GMO may transfer up to $200 million of unused commitments between Great Plains Energy's and GMO's facilities. A default by GMO or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times. At December 31, 2017, GMO was in compliance with this covenant. At December 31, 2017, GMO had $209.3 million of commercial paper outstanding at a weighted-average interest rate of 1.85%, had issued letters of credit totaling $2.1 million and had no outstanding cash borrowings under the credit facility. At December 31, 2016, GMO had $201.9 million of commercial paper outstanding at a weighted-average interest rate of 1.02%, had issued letters of credit totaling $1.9 million and had no outstanding cash borrowings under the credit facility. Great Plains Energy's $864.5 Million Term Loan Facility In connection with the Original Merger Agreement, Great Plains Energy entered into a commitment letter for a 364-day senior unsecured bridge term loan facility, originally for an aggregate principal amount of $8.017 billion to support the anticipated transaction and provide flexibility for the timing of long-term financing. Following Great Plains Energy's completed acquisition financings, the aggregate principal amount of the facility was subsequently reduced to $864.5 million and the expiration date of the facility was extended to November 30, 2017. The remaining commitment of $864.5 million was terminated in July 2017 in connection with the Amended Merger Agreement.

Long-Term Debt

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Long-Term Debt

12. LONG-TERM DEBT

Great Plains Energy's and KCP&L's long-term debt is detailed in the following table.



		December 31
	Year Due	2017				2016
KCP&L			(millions)
General Mortgage Bonds
2.95% EIRR bonds	2023		$	79.5			$	110.5
7.15% Series 2009A (8.59% rate)^(a)	2019		400.0				400.0
Senior Notes
5.85% Series (5.72% rate)^(a)			—				250.0
6.375% Series (7.49% rate)^(a)	2018		350.0				350.0
3.15% Series	2023		300.0				300.0
3.65% Series	2025		350.0				350.0
6.05% Series (5.78% rate)^(a)	2035		250.0				250.0
5.30% Series	2041		400.0				400.0
4.20% Series	2047		300.0				—
EIRR Bonds
1.329% Series 2007A and 2007B^(b)	2035		146.5				146.5
2.875% Series 2008	2038		23.4				23.4
Current maturities			(350.0		)		(281.0		)
Unamortized discount and debt issuance costs			(17.2		)		(15.4		)
Total KCP&L excluding current maturities^(c)			2,232.2				2,284.0
Other Great Plains Energy
GMO First Mortgage Bonds 9.44% Series	2018-2021		4.6				5.7
GMO Senior Notes
8.27% Series	2021		80.9				80.9
3.49% Series A	2025		125.0				125.0
4.06% Series B	2033		75.0				75.0
4.74% Series C	2043		150.0				150.0
GMO Medium Term Notes
7.33% Series	2023		3.0				3.0
7.17% Series	2023		7.0				7.0
Great Plains Energy Senior Notes
6.875% Series (7.33% rate)^(a)			—				100.0
4.85% Series	2021		350.0				350.0
5.292% Series	2022		287.5				287.5
Current maturities			(1.1		)		(101.1		)
Unamortized discount and premium, net and debt issuance costs			(1.5		)		(1.8		)
Total Great Plains Energy excluding current maturities^(c)			$	3,312.6			$	3,365.2


^(a)	Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments


^(b)	Variable rate


^(c)	At December 31, 2017 and 2016, does not include $50.0 million and $21.9 million of secured Series 2005 Environmental Improvement Revenue Refunding (EIRR) bonds because the bonds were repurchased in September 2015 and are held by KCP&L

Amortization of Debt Expense

Great Plains Energy's and KCP&L's amortization of debt expense is detailed in the following table.



	2017		2016		2015
	(millions)
KCP&L	$	3.0	$	3.2	$	3.0
Other Great Plains Energy	26.9		30.6		1.1
Total Great Plains Energy	$	29.9	$	33.8	$	4.1

In 2017 and 2016, Other Great Plains Energy includes $23.6 million and $29.6 million, respectively, of amortization of debt expense related to Great Plains Energy's bridge term loan facility. Fees related to this facility were amortized over the term of the facility.

KCP&L General Mortgage Bonds

KCP&L has issued mortgage bonds under the Indenture. The Indenture creates a mortgage lien on substantially all of KCP&L's utility plant. Mortgage bonds totaling $479.5 million and $510.5 million were outstanding at December 31, 2017 and 2016, respectively. KCP&L repaid its $31.0 million secured Series 1992 EIRR bonds at maturity in July 2017.

KCP&L Senior Notes

In June 2017, KCP&L issued, at a discount, $300.0 million of 4.20% unsecured Senior Notes, maturing in 2047. KCP&L also repaid its $250.0 million of 5.85% unsecured Senior Notes at maturity in June 2017.

KCP&L Municipal Bond Insurance Policies

KCP&L's secured Series 2005 EIRR bonds totaling $50.0 million and $21.9 million, respectively, are covered by a municipal bond insurance policy between KCP&L and Syncora Guarantee, Inc. (Syncora). The insurance agreements between KCP&L and Syncora provide for reimbursement by KCP&L for any amounts that Syncora pays under the municipal bond insurance policies. The insurance agreements contain a covenant that the indebtedness to total capitalization ratio of KCP&L and its consolidated subsidiaries will not be greater than 0.68 to 1.00. At December 31, 2017, KCP&L was in compliance with this covenant. KCP&L is also restricted from issuing additional bonds under its General Mortgage Indenture if, after giving effect to such additional bonds, the proportion of secured debt to total indebtedness would be more than 75%, or more than 50% if the long term rating for such bonds by S&P Global Ratings or Moody's Investors Service would be at or below A- or A3, respectively. The insurance agreement covering the unsecured Series 2005 EIRR bonds also required KCP&L to provide collateral to Syncora in the form of $50.0 million of Mortgage Bonds Series 2005 EIRR Insurer due 2035 for KCP&L's obligations under the insurance agreement as a result of KCP&L issuing general mortgage bonds in 2009 (other than refunding of outstanding general mortgage bonds) that resulted in the aggregate amount of outstanding general mortgage bonds exceeding 10% of total capitalization. The bonds are not incremental debt for KCP&L but collateralize Syncora's claim on KCP&L if Syncora was required to meet its obligation under the insurance agreement. In the event of a default under the insurance agreements, Syncora may take any available legal or equitable action against KCP&L, including seeking specific performance of the covenants.

GMO First Mortgage Bonds

GMO has issued mortgage bonds under the General Mortgage Indenture and Deed of Trust dated April 1, 1946, as supplemented. The Indenture creates a mortgage lien on a portion of GMO's utility plant. Mortgage bonds totaling $4.6 million and $5.7 million, respectively, were outstanding at December 31, 2017 and 2016.

GMO Senior Notes

Under the terms of the note purchase agreement for GMO's Series A, B and C Senior Notes, GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement. At December 31, 2017, GMO was in compliance with these covenants.

Great Plains Energy Senior Notes

In March 2017, Great Plains Energy issued $4.3 billion of senior notes in order to fund the majority of the cash portion of the acquisition of Westar under the Original Merger Agreement.

In July 2017, as a result of the Amended Merger Agreement, Great Plains Energy determined in its reasonable judgment that the acquisition of Westar would not close prior to November 30, 2017 and exercised its special optional redemption right to redeem the senior notes issued in March 2017. The redemption price was equal to 101% of the principle amount of the senior notes, including accrued and unpaid interest, for a total redemption cost of $4,400.1 million. As a result of the redemption, Great Plains Energy recorded a loss on extinguishment of debt of $82.8 million in July 2017.

Great Plains Energy repaid its $100.0 million of 6.875% unsecured Senior Notes at maturity in September 2017.

Scheduled Maturities

Great Plains Energy's and KCP&L's long-term debt maturities for the next five years are detailed in the following table.



	2018		2019		2020		2021		2022
	(millions)
Great Plains Energy	$	351.1	$	401.1	$	1.1	$	432.0	$	287.5
KCP&L	350.0		400.0		—		—		—

Common Shareholders' Equity	12 Months Ended
Common Shareholders' Equity	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Common Shareholders' Equity	13. COMMON STOCK Great Plains Energy has an effective shelf registration statement for the sale of unlimited amounts of securities with the SEC that became effective in March 2015 and expires in March 2018. In September 2016, Great Plains Energy filed a post-effective amendment to its shelf registration statement to register depositary shares and preference stock among the types of securities that Great Plains Energy may offer and sell. Great Plains Energy does not expect to replace this shelf registration statement prior to the closing of the anticipated merger with Westar. In September 2016, Great Plains Energy shareholders approved an amendment to Great Plains Energy's articles of incorporation, increasing the authorized number of shares of common stock, without par value, to 600 million shares from 250 million shares. In October 2016, Great Plains Energy completed a registered public offering of 60.5 million shares of common stock, without par value, at a public offering price of $26.45 per share, for total gross proceeds of approximately $1.6 billion (net proceeds of approximately $1.55 billion after issuance costs). Great Plains Energy planned to use proceeds from the offering to finance a portion of the cash consideration for the acquisition of Westar under the Original Merger Agreement. Great Plains Energy has shares of common stock registered with the SEC for its Dividend Reinvestment and Direct Stock Purchase Plan. The plan allows for the purchase of common shares by reinvesting dividends or making optional cash payments. Great Plains Energy can issue new shares or purchase shares on the open market for the plan. At December 31, 2017, 0.9 million shares remained available for future issuances. Great Plains Energy has shares of common stock registered with the SEC for a defined contribution savings plan (401(k)). Shares issued under the plan may be either newly issued shares or shares purchased in the open market. At December 31, 2017, 0.5 million shares remained available for future issuances. Treasury shares are held for future distribution upon issuance of shares in conjunction with the Company's Long-Term Incentive Plan. Great Plains Energy's articles of incorporation restrict the payment of common stock dividends in the event common equity is 25% or less of total capitalization. Certain conditions in the MPSC and KCC orders authorizing the holding company structure require Great Plains Energy and KCP&L to maintain consolidated common equity of at least 30% and 35%, respectively, of total capitalization (including only the amount of short-term debt in excess of the amount of construction work in progress). Under the Federal Power Act, KCP&L and GMO generally can pay dividends only out of retained earnings. The revolving credit agreements of Great Plains Energy, KCP&L and GMO and the note purchase agreement for GMO's Series A, B and C Senior Notes contain a covenant requiring the respective company to maintain a consolidated indebtedness to consolidated total capitalization ratio of not more than 0.65 to 1.00 at all times. Under the Amended Merger Agreement, Great Plains Energy is also restricted from paying a quarterly common stock dividend in excess of $0.275 per share without the consent of Westar. As of December 31, 2017, all of Great Plains Energy's and KCP&L's retained earnings and net income were free of restrictions. As a result of the above restrictions, Great Plains Energy's subsidiaries had restricted net assets of approximately $2.8 billion as of December 31, 2017. The restrictions are not expected to affect the Companies' ability to pay dividends at the current level in the foreseeable future.

Preferred Stock	12 Months Ended
Preferred Stock	Dec. 31, 2017
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock [Text Block]	14. PREFERRED STOCK At December 31, 2017, 1.6 million shares of Cumulative No Par Preferred Stock, 390,000 shares of Cumulative Preferred Stock, $100 par value and 11.0 million shares of no par Preference Stock were authorized under Great Plains Energy's articles of incorporation. Series A Mandatory Convertible Preferred Stock On May 29, 2016, Great Plains Energy entered into a stock purchase agreement with OMERS, pursuant to which Great Plains Energy would issue and sell to OMERS 750,000 shares of Series A Preferred Stock, for an aggregate purchase price equal to $750 million at the closing of the Original Merger Agreement. In July 2017, as a result of the Amended Merger Agreement, Great Plains Energy and OMERS terminated their stock purchase agreement for the Series A Preferred Stock. As a result of this termination, Great Plains Energy recorded $15 million of previously deferred offering fees to non-operating expenses in the third quarter of 2017. Series B Mandatory Convertible Preferred Stock In October 2016, Great Plains Energy completed a registered public offering of 17.3 million depositary shares, each representing a 1/20th interest in a share of Great Plains Energy's Series B Preferred Stock, without par value, at a public offering price of $50 per depositary share for total gross proceeds of $862.5 million (net proceeds of approximately $836.2 million after issuance costs). Great Plains Energy planned to use proceeds from the offering to fund a portion of the cash consideration for the acquisition of Westar under the Original Merger Agreement. Each depositary share entitled the holder of such depositary share, through the bank depositary, to a 1/20th interest in the rights and preferences of the Series B Preferred Stock, including conversion, dividend, liquidation and voting rights, subject to the terms of the deposit agreement. Unless previously converted or redeemed, on or around September 15, 2019, each outstanding share of Series B Preferred Stock would automatically convert into a number of shares of Great Plains Energy common stock equal to a conversion rate. Dividends on the Series B Preferred Stock were payable on a cumulative basis when, as and if declared by Great Plains Energy's Board of Directors, and subject to Missouri law, at an annual rate of 7.00% on the liquidation preference of $1,000 per share of Series B Preferred Stock (or $50 per depositary share), payable in cash, Great Plains Energy common stock or a combination thereof. Great Plains Energy's Series B Preferred Stock also contained an acquisition termination redemption option whereby in the event that the Original Merger Agreement was terminated or if Great Plains Energy determined in its reasonable judgment that the acquisition of Westar would not close or if the acquisition of Westar had not closed by November 30, 2017, then Great Plains Energy could at its sole option (but was not required to) redeem all of the Series B Preferred Stock. If exercised, the redemption price would be equal to either: (a) $1,000 per share plus accumulated and unpaid dividends up to the redemption date; or (b) if the average price of Great Plains Energy's common stock exceeded a certain threshold amount, then a repurchase price that is equal to a make-whole formula. The Series B Preferred Stock also contained a fundamental change conversion option whereby upon the occurrence of certain events deemed to be a fundamental change, including an acquisition, liquidation, or delisting of Great Plains Energy common stock, holders of the Series B Preferred Stock could: (a) convert their existing shares into shares of Great Plains Energy common stock; and (b) receive a dividend make-whole payment. As a result of the Amended Merger Agreement, Great Plains Energy determined in its reasonable judgment that the acquisition of Westar under the Original Merger Agreement would not close and exercised its acquisition termination redemption option and redeemed the Series B Preferred Stock in August 2017. The Series B Preferred Stock was redeemed at a redemption price that was equal to a make-whole formula set forth in the terms of the Series B Preferred Stock. The total cost of the redemption was $963.4 million. Great Plains Energy made the entire redemption payment in cash. The dividend make-whole provisions within both the acquisition termination redemption and fundamental change conversion options discussed above represented embedded derivatives that in accordance with GAAP, were accounted for on a combined basis separately from the Series B Preferred Stock and reported at fair value. The fair value of the Series B Preferred Stock dividend make-whole provisions at inception and December 31, 2016 was insignificant. As part of the $963.4 million redemption of the Series B Preferred Stock, the Series B Preferred Stock dividend make-whole provisions liability was settled in August 2017. In 2017, Great Plains Energy recognized a loss of $124.8 million for the settlement of these provisions, which is recorded within loss on Series B Preferred Stock dividend make-whole provisions on the consolidated statements of comprehensive income (loss). Great Plains Energy also recognized a redemption premium of $2.4 million in connection with the redemption of the Series B Preferred Stock in 2017. This premium is represented as the difference between the redemption cost of $963.4 million and the $836.2 million carrying value of the Series B Preferred Stock, less the $124.8 million paid to settle the Series B Preferred Stock dividend make-whole provisions. The redemption premium is recorded as a reduction to earnings (loss) available for common shareholders and is recorded within preferred stock dividend requirements and redemption premium on the consolidated statements of comprehensive income (loss).

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

15. COMMITMENTS AND CONTINGENCIES

Environmental Matters

Great Plains Energy and KCP&L are subject to extensive federal, state and local environmental laws, regulations and permit requirements relating to air and water quality, waste management and disposal, natural resources and health and safety. In addition to imposing continuing compliance obligations and remediation costs, these laws, regulations and permits authorize the imposition of substantial penalties for noncompliance, including fines, injunctive relief and other sanctions. The cost of complying with current and future environmental requirements is expected to be material to Great Plains Energy and KCP&L. Failure to comply with environmental requirements or to timely recover environmental costs through rates could have a material effect on Great Plains Energy's and KCP&L's results of operations, financial position and cash flows.

Great Plains Energy's and KCP&L's current estimates of capital expenditures (exclusive of AFUDC and property taxes) over the next five years to comply with environmental regulations are in the following table. The total cost of compliance with any existing, proposed or future laws and regulations may be significantly different from these cost estimates provided.



	2018		2019		2020		2021		2022
	(millions)
Great Plains Energy	$	14.6	$	2.8	$	7.7	$	20.1	$	63.1
KCP&L	14.5		2.8		7.7		20.1		63.1

The Companies expect to seek recovery of the costs associated with environmental requirements through rate increases; however, there can be no assurance that such rate increases would be granted. The Companies may be subject to materially adverse rate treatment in response to competitive, economic, political, legislative or regulatory factors and/or public perception of the Companies' environmental reputation.

The following discussion groups environmental and certain associated matters into the broad categories of air and climate change, water, solid waste and remediation.

Clean Air Act and Climate Change Overview

The Clean Air Act Amendments of 1990 (Clean Air Act) and associated regulations enacted by the EPA form a comprehensive program to preserve and enhance air quality. States are required to establish regulations and programs to address all requirements of the Clean Air Act and have the flexibility to enact more stringent requirements. All of Great Plains Energy's and KCP&L's generating facilities, and certain of their other facilities, are subject to the Clean Air Act.

Climate Change

The Companies' current generation capacity is primarily coal-fired and is estimated to produce about one ton of carbon dioxide (CO₂) per MWh, or approximately 17 million tons and 13 million tons per year for Great Plains Energy and KCP&L, respectively. The Companies are subject to existing greenhouse gas reporting regulations and certain greenhouse gas requirements. Federal or state legislation concerning the reduction of emissions of greenhouse gases, including CO₂, could be enacted in the future. At the international level, the Paris Agreement was adopted in December 2015 by nearly 200 countries and became effective in November 2016. The Paris Agreement does not result in any new, legally binding obligations on the U.S. to meet a particular greenhouse gas emissions target, but establishes a framework for international cooperation on climate change. In June 2017, U.S. President Donald Trump announced the U.S. would withdraw from the Paris Agreement. Under the rules of the Paris Agreement, the earliest any country can withdraw is November 2020. Other international agreements legally binding on the U.S. may be reached in the future. Greenhouse gas legislation has the potential of having significant financial and operational impacts on Great Plains Energy and KCP&L; however, the ultimate financial and operational consequences to Great Plains Energy and KCP&L cannot be determined until such legislation is passed. In the absence of new Congressional mandates, the EPA is proceeding with the regulation of greenhouse gases under the existing Clean Air Act.

In August 2015, the EPA finalized CO₂ emission standards for new, modified and reconstructed affected fossil-fuel-fired electric utility generating units. The standards would not apply to Great Plains Energy's and KCP&L's existing units unless the units were modified or reconstructed in the future. Also in August 2015, the EPA finalized its Clean Power Plan which sets CO₂ emission performance rates for existing affected fossil-fuel-fired electric generating units. Nationwide, by 2030, the EPA projects the Clean Power Plan would achieve CO₂ emission reductions from the power sector of approximately 32% from CO₂ emission levels in 2005.

In February 2016, the U.S. Supreme Court granted a stay of the Clean Power Plan putting the rule on hold pending review in the U.S. Court of Appeals for the District of Columbia Circuit and any subsequent review by the U.S. Supreme Court if such review is sought. In October 2017, the EPA proposed to repeal the Clean Power Plan on the basis that it exceeded the EPA’s statutory authority. In December 2017, the EPA issued an advance notice of proposed rulemaking (ANPRM) to solicit comments as the agency considers proposing a future rule to replace the Clean Power Plan. In the ANPRM, the EPA is considering proposing emission guidelines to limit greenhouse gas emissions from existing electric utility generating units. Compliance with the Clean Power Plan or any replacement rule has the potential of having significant financial and operational impacts on Great Plains Energy and KCP&L; however, the ultimate financial and operational consequences to Great Plains Energy and KCP&L cannot be determined until the outcome of the EPA's proposal to repeal the Clean Power Plan and pending litigation is known.

Clean Water Act

The Clean Water Act and associated regulations enacted by the EPA form a comprehensive program to restore and preserve water quality. Like the Clean Air Act, states are required to establish regulations and programs to address all requirements of the Clean Water Act, and have the flexibility to enact more stringent requirements. All of Great Plains Energy's and KCP&L's generating facilities, and certain of their other facilities, are subject to the Clean Water Act.

In May 2014, the EPA finalized regulations pursuant to Section 316(b) of the Clean Water Act regarding cooling water intake structures pursuant to a court approved settlement. KCP&L generation facilities with cooling water intake structures are subject to the best technology available standards based on studies completed to comply with such standards. The rule provides flexibility to work with the states to develop the best technology available to minimize aquatic species impacted by being pinned against intake screens (impingement) or drawn into cooling water systems (entrainment). Estimated costs to comply with Section 316(b) of the Clean Water Act are included in the estimated capital expenditures table above.

KCP&L holds a permit from the Missouri Department of Natural Resources (MDNR) covering water discharge from its Hawthorn Station. The permit authorizes KCP&L to, among other things, withdraw water from the Missouri River for cooling purposes and return the heated water to the Missouri River. KCP&L has applied for a renewal of this permit and the EPA has submitted an interim objection letter regarding the allowable amount of heat that can be contained in the returned water. Until this matter is resolved, KCP&L continues to operate under its current permit. Great Plains Energy and KCP&L cannot predict the outcome of this matter; however, while less significant outcomes are possible, this matter may require a reduction in generation, installation of cooling towers or other technology to cool the water, or both, any of which could have a significant impact on Great Plains Energy's and KCP&L's results of operations, financial position and cash flows.

Solid Waste

Solid and hazardous waste generation, storage, transportation, treatment and disposal are regulated at the federal and state levels under various laws and regulations. In December 2014, the EPA finalized regulations to regulate coal combustion residuals (CCRs) under the Resource Conservation and Recovery Act (RCRA) subtitle D to address the risks from the disposal of CCRs generated from the combustion of coal at electric generating facilities. The Companies use coal in generating electricity and dispose of the CCRs in both on-site facilities and facilities owned by third parties. KCP&L's Iatan, La Cygne, and Montrose Stations and GMO's Sibley Station have on-site facilities affected by the rule. The rule requires periodic assessments; groundwater monitoring; location restrictions; design and operating requirements; recordkeeping and notifications; and closure, among other requirements, for CCR units. The rule was promulgated in the Federal Register on April 17, 2015, and became effective six months after promulgation with various obligations effective at specified times within the rule. Estimated capital costs to comply with the CCR rule are included in the estimated capital expenditures table above. Certain requirements of the rule would require Great Plains Energy or KCP&L to expedite or incur additional capital expenditures in the future.

Great Plains Energy and KCP&L have AROs on their balance sheets for closure and post-closure of ponds and landfills containing CCRs. Certain requirements of the rule could in the future require further evaluation of the expected method of compliance and refinement of assumptions underlying the cost estimates for closure and post-closure. Great Plains Energy's and KCP&L's AROs could increase from the amounts presently recorded.

Remediation

Certain federal and state laws, including the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), hold current and previous owners or operators of contaminated facilities and persons who arranged for the disposal or treatment of hazardous substances liable for the cost of investigation and cleanup. CERCLA and other laws also authorize the EPA and other agencies to issue orders compelling potentially responsible parties to clean up sites that are determined to present an actual or potential threat to human health or the environment. GMO retains some environmental liability for several operations and investments it no longer owns. In addition, GMO also owns, or has acquired liabilities from companies that once owned or operated, former manufactured gas plant (MGP) sites, which are subject to the supervision of the EPA and various state environmental agencies.

At December 31, 2017 and 2016, KCP&L had $0.3 million accrued for environmental remediation expenses, which covers ground water monitoring at a former MGP site. The amount accrued was established on an undiscounted basis and KCP&L does not currently have an estimated time frame over which the accrued amount may be paid.

In addition to the $0.3 million accrual above, at December 31, 2017 and 2016, Great Plains Energy had $1.5 million and $1.4 million, respectively, accrued for the future investigation and remediation of certain additional GMO identified MGP sites and retained liabilities. This estimate was based upon review of the potential costs associated with conducting investigative and remedial actions at identified sites, as well as the likelihood of whether such actions will be necessary. This estimate could change materially after further investigation, and could also be affected by the actions of environmental agencies and the financial viability of other potentially responsible parties; however, given the uncertainty of these items the possible loss or range of loss in excess of the amount accrued is not estimable.

GMO has pursued recovery of remediation costs from insurance carriers and other potentially responsible parties. As a result of a settlement with an insurance carrier, approximately $1.6 million in insurance proceeds less an annual deductible is available to GMO to recover qualified MGP remediation expenses. GMO would seek recovery of additional remediation costs and expenses through rate increases; however, there can be no assurance that such rate increases would be granted.

Contractual Commitments

Great Plains Energy's and KCP&L's expenses related to lease commitments are detailed in the following table.



	2017		2016		2015
	(millions)
Great Plains Energy	$	14.2	$	15.0	$	16.8
KCP&L	13.1		13.7		15.0

Great Plains Energy's and KCP&L's contractual commitments at December 31, 2017, excluding pensions and long-term debt, are detailed in the following tables.



Great Plains Energy
	2018		2019		2020		2021		2022		After 2022			Total
Lease commitments	(millions)
Operating lease	$	12.1	$	9.3	$	9.7	$	9.7	$	9.5		$	101.0		$	151.3
Capital lease	0.4		0.4		0.4		0.4		0.4			2.7			4.7
Purchase commitments
Fuel	210.4		180.1		67.3		5.1		37.4			80.7			581.0
Power	47.3		47.3		47.3		47.4		47.6			414.6			651.5
Other	20.9		14.7		6.7		5.5		2.4			35.9			86.1
Total contractual commitments	$	291.1	$	251.8	$	131.4	$	68.1	$	97.3		$	634.9		$	1,474.6



KCP&L
	2018		2019		2020		2021		2022		After 2022			Total
Lease commitments	(millions)
Operating lease	$	11.3	$	9.3	$	9.7	$	9.7	$	9.5		$	101.0		$	150.5
Capital lease	0.2		0.2		0.2		0.2		0.2			1.4			2.4
Purchase commitments
Fuel	177.5		159.8		51.8		5.1		37.4			80.7			512.3
Power	34.8		34.8		34.8		34.9		35.1			289.8			464.2
Other	20.0		12.7		5.8		4.6		1.6			31.4			76.1
Total contractual commitments	$	243.8	$	216.8	$	102.3	$	54.5	$	83.8		$	504.3		$	1,205.5

Great Plains Energy's and KCP&L's lease commitments end in 2048. Operating lease commitments include rail cars to serve jointly-owned generating units where KCP&L is the managing partner. Of the amounts included in the table above, KCP&L will be reimbursed by the other owners for approximately $1.2 million in 2018 and approximately $0.4 million per year from 2019 to 2025, for a total of $4.0 million.

Fuel commitments consist of commitments for nuclear fuel, coal and coal transportation. Power commitments consist of commitments for renewable energy under power purchase agreements. Other represents individual commitments entered into in the ordinary course of business.

Legal Proceedings	12 Months Ended
Legal Proceedings	Dec. 31, 2017
Legal Proceedings [Abstract]
Contingencies Disclosure [Text Block]	16. LEGAL PROCEEDINGS GMO Western Energy Crisis In response to complaints of excessive prices in the California energy markets, FERC issued an order in July 2001 requiring net sellers of power in the California markets from October 2, 2000, through June 20, 2001, at prices above a FERC-determined competitive market clearing price, to make refunds to net purchasers of power in the California market during that time period. MPS Merchant was a net purchaser of power during the refund period. In November 2014, FERC issued an order finding that MPS Merchant engaged in tariff violations during the periods prior to October 2, 2000 (the Summer Period) and ordered refunds in the form of disgorgement of certain revenues. In November 2015 and February 2016, FERC issued additional orders regarding the refunds MPS Merchant owed. In October 2016, MPS Merchant reached a settlement agreement, which was subsequently revised in February 2017, with certain California utilities and governmental agencies that would settle all issues in the case in exchange for $7.5 million of cash consideration as well as MPS Merchant's interest in additional funds it was entitled to during the refund period discussed above. In September 2017, the settlement agreement was approved by FERC and the settlement payment was made by MPS Merchant in October 2017. In accordance with the terms of the settlement agreement, the $7.5 million of cash consideration accrued interest at the FERC interest rate beginning on January 1, 2017, until the date of the payment of the settlement. At December 31, 2016, Great Plains Energy had accrued for the cash consideration pursuant to the settlement agreement.

Guarantees

12 Months Ended

Dec. 31, 2017

Guarantees [Abstract]

Guarantees [Text Block]

17. GUARANTEES

In the ordinary course of business, Great Plains Energy and certain of its subsidiaries enter into various agreements providing financial or performance assurance to third parties on behalf of certain subsidiaries. Such agreements include, for example, guarantees and letters of credit. These agreements are entered into primarily to support or enhance the creditworthiness otherwise attributed to a subsidiary on a stand-alone basis, thereby facilitating the extension of sufficient credit to accomplish the subsidiary's intended business purposes. The majority of these agreements guarantee the Company's own future performance, so a liability for the fair value of the obligation is not recorded.

At December 31, 2017, Great Plains Energy has provided $133.5 million of credit support for GMO as follows:


•	Great Plains Energy direct guarantees to GMO counterparties totaling $38.0 million, which expire in 2018 and


•	Great Plains Energy guarantee of GMO long-term debt totaling $95.5 million, which includes debt with maturity dates ranging from 2018 to 2023.

Great Plains Energy has also guaranteed GMO's commercial paper program. At December 31, 2017, GMO had $209.3 million commercial paper outstanding.

Related Party Transactions and Relationships

12 Months Ended

Dec. 31, 2017

18. RELATED PARTY TRANSACTIONS AND RELATIONSHIPS

KCP&L employees manage GMO's business and operate its facilities at cost, including GMO's 18% ownership interest in KCP&L's Iatan Nos. 1 and 2. The operating expenses and capital costs billed from KCP&L to GMO were $196.3 million for 2017, $194.4 million for 2016 and $183.6 million for 2015.

KCP&L and GMO are also authorized to participate in the Great Plains Energy money pool, an internal financing arrangement in which funds may be lent on a short-term basis to KCP&L and GMO from Great Plains Energy and between KCP&L and GMO. At December 31, 2017 and 2016, KCP&L had no outstanding receivables or payables under the money pool.

The following table summarizes KCP&L's related party net receivables.



	December 31
	2017		2016
	(millions)
Net receivable from GMO	$	65.8	$	64.6
Net receivable from Great Plains Energy	18.9		2.6

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

19. FAIR VALUE MEASUREMENTS

GAAP defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. GAAP establishes a fair value hierarchy, which prioritizes the inputs to valuation techniques used to measure fair value into three broad categories, giving the highest priority to quoted prices in active markets for identical assets or liabilities and lowest priority to unobservable inputs. A definition of the various levels, as well as discussion of the various measurements within the levels, is as follows:

Level 1 – Unadjusted quoted prices for identical assets or liabilities in active markets that Great Plains Energy and KCP&L have access to at the measurement date.

Level 2 – Market-based inputs for assets or liabilities that are observable (either directly or indirectly) or inputs that are not observable but are corroborated by market data.

Level 3 – Unobservable inputs, reflecting Great Plains Energy's and KCP&L's own assumptions about the assumptions market participants would use in pricing the asset or liability.

Great Plains Energy and KCP&L record cash and cash equivalents and short-term borrowings on the balance sheet at cost, which approximates fair value due to the short-term nature of these instruments.

Interest Rate Derivatives

In June 2016, Great Plains Energy entered into four interest rate swaps, with a total notional amount of $4.4 billion, to hedge against interest rate fluctuations on future issuances of long-term debt expected to be issued to finance a portion of the cash consideration for the acquisition of Westar under the Original Merger Agreement. The interest rate swaps were designated as economic hedges (non-hedging derivatives). Settlement of the interest rate swaps was contingent on the consummation of the acquisition of Westar. In March 2017, in connection with Great Plains Energy's $4.3 billion senior note issuance, the settlement value of the interest rate swaps to Great Plains Energy of $140.6 million was fixed.

In July 2017, the interest rate swap agreements were amended to make their cash settlement contingent on the consummation of the anticipated merger with Westar under the Amended Merger Agreement by November 30, 2018. Also in July 2017, Great Plains Energy redeemed its $4.3 billion senior notes that the interest rate swaps were entered into to hedge.

The fair value of the interest rate swaps recorded on Great Plains Energy's balance sheets reflects a contingency factor that management believes is representative of what a market participant would use in valuing these instruments in order to account for the contingent nature of the cash settlement of the interest rate swaps. The contingency factor was 0.35 at December 31, 2017 and 2016. At December 31, 2017 and 2016, the fair value of the interest rate swaps was $91.4 million and $79.3 million, respectively, and was recorded on the consolidated balance sheets in interest rate derivative instruments.

Due to the redemption of Great Plains Energy’s $4.3 billion senior notes in July 2017 and the fact that the interest rate swaps no longer serve as economic hedges, Great Plains Energy recorded changes in the fair value of the interest rate swaps after July 2017 in non-operating income on Great Plains Energy’s consolidated statements of comprehensive income (loss). All changes in the fair value of the interest rate swaps prior to July 2017 were recorded in interest charges. For 2017 and 2016, Great Plains Energy recognized gains of $12.1 million and $79.3 million, respectively, for the change in fair value of the interest rate swaps. Of these amounts, $14.0 million of gains were recorded in non-operating income in 2017.

Fair Value of Long-Term Debt

Great Plains Energy and KCP&L record long-term debt on the balance sheet at amortized cost. The fair value of long-term debt is measured as a Level 2 liability and is based on quoted market prices, with the incremental borrowing rate for similar debt used to determine fair value if quoted market prices are not available. At December 31, 2017, the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.7 billion and $4.0 billion, respectively. At December 31, 2016, the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.8 billion and $4.0 billion, respectively. At December 31, 2017, the book value and fair value of KCP&L's long-term debt, including current maturities, were $2.6 billion and $2.8 billion, respectively. At December 31, 2016, the book value and fair value of KCP&L's long-term debt, including current maturities, were $2.6 billion and $2.7 billion, respectively.

Supplemental Executive Retirement Plan

At December 31, 2017 and 2016, GMO's SERP rabbi trusts included $14.7 million and $16.0 million, respectively, of fixed income funds valued at net asset value per share (or its equivalent) that are not categorized in the fair value hierarchy. The fixed income fund invests primarily in intermediate and long-term debt securities, can be redeemed immediately and is not subject to any restrictions on redemptions.

The following tables include Great Plains Energy's and KCP&L's balances of financial assets and liabilities measured at fair value on a recurring basis.



Description	December 31 2017			Level 1		Level 2			Level 3
KCP&L		(millions)
Assets
Nuclear decommissioning trust ^(a)
Equity securities		$	183.8	$	183.8		$	—		$	—
Debt securities
U.S. Treasury		35.3		35.3			—			—
U.S. Agency		0.4		—			0.4			—
State and local obligations		2.1		—			2.1			—
Corporate bonds		34.1		—			34.1			—
Foreign governments		0.1		—			0.1			—
Cash equivalents		2.5		2.5			—			—
Other		0.1		0.1			—			—
Total nuclear decommissioning trust		258.4		221.7			36.7			—
Self-insured health plan trust ^(b)
Equity securities		0.5		0.5			—			—
Debt securities		2.7		0.3			2.4			—
Cash and cash equivalents		7.7		7.7			—			—
Total self-insured health plan trust		10.9		8.5			2.4			—
Total		$	269.3	$	230.2		$	39.1		$	—
Other Great Plains Energy
Assets
Interest rate derivative instruments ^(c)		$	91.4	$	—		$	—		$	91.4
Total		$	91.4	$	—		$	—		$	91.4
Great Plains Energy
Assets
Nuclear decommissioning trust ^(a)		$	258.4	$	221.7		$	36.7		$	—
Self-insured health plan trust ^(b)		10.9		8.5			2.4			—
Interest rate derivative instruments ^(c)		91.4		—			—			91.4
Total		$	360.7	$	230.2		$	39.1		$	91.4



Description	December 31 2016			Level 1			Level 2			Level 3
KCP&L		(millions)
Assets
Nuclear decommissioning trust ^(a)
Equity securities		$	153.9		$	153.9		$	—		$	—
Debt securities
U.S. Treasury		27.8			27.8			—			—
U.S. Agency		1.7			—			1.7			—
State and local obligations		3.2			—			3.2			—
Corporate bonds		32.4			—			32.4			—
Foreign governments		0.1			—			0.1			—
Cash equivalents		3.8			3.8			—			—
Total nuclear decommissioning trust		222.9			185.5			37.4			—
Self-insured health plan trust ^(b)
Equity securities		0.9			0.9			—			—
Debt securities		4.8			0.1			4.7			—
Cash and cash equivalents		5.6			5.6			—			—
Total self-insured health plan trust		11.3			6.6			4.7			—
Total		$	234.2		$	192.1		$	42.1		$	—
Other Great Plains Energy
Assets
Interest rate derivative instruments ^(c)		$	79.3		$	—		$	—		$	79.3
Total		$	79.3		$	—		$	—		$	79.3
Great Plains Energy
Assets
Nuclear decommissioning trust ^(a)		$	222.9		$	185.5		$	37.4		$	—
Self-insured health plan trust ^(b)		11.3			6.6			4.7			—
Interest rate derivative instruments ^(c)		79.3			—			—			79.3
Total		$	313.5		$	192.1		$	42.1		$	79.3


^(a)	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.


^(b)	Fair value is based on quoted market prices of the investments held by the trust. Debt securities classified as Level 1 are comprised of U.S. Treasury securities. Debt securities classified as Level 2 are comprised of corporate bonds, U.S. Agency, state and local obligations, and other asset-backed securities.

^(c)

At December 31, 2017, the fair value of interest rate derivative instruments is based on the settlement value of $140.6 million discounted by a contingency factor of 0.35 that management believes is representative of what a market participant would use in valuing these instruments in order to account for the contingent nature of the cash settlement of these instruments. At December 31, 2016, the fair value of interest rate derivative instruments is determined by calculating the net present value of expected payments and receipts under the interest rate swaps using observable market inputs including interest rates and London Interbank Offered Rate swap rates discounted by a contingency factor of 0.35. A decrease in the contingency factor would result in a higher fair value measurement. The contingency factor will increase or decrease in response to facts and circumstances that in the view of a market participant, would increase or decrease the likelihood that the merger with Westar is not consummated. Because of the unobservable nature of the contingency factor, the interest rate derivatives have been classified as Level 3.

The following table reconciles the beginning and ending balances for all Level 3 assets measured at fair value on a recurring basis.



Great Plains Energy
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2017			2016
	(millions)
Net asset at January 1	$	79.3		$	—
Total realized/unrealized gains (losses):
included in interest charges	(1.9		)	79.3
included in non-operating income	14.0			—
included in loss on Series B Preferred Stock dividend make-whole provisions	(124.8		)	—
Settlements	124.8			—
Net asset at December 31	$	91.4		$	79.3
Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at December 31:
included in interest charges	$	(1.9	)	$	79.3
included in non-operating income	$	14.0		$	—

See Note 14 for additional information concerning the Series B Preferred Stock dividend make-whole provisions.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Accumulated Other Comprehensive Income (Loss)

12 Months Ended

Dec. 31, 2017

Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]

Accumulated Other Comprehensive Income (Loss) [Text Block]

20. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)

The following tables reflect the change in the balances of each component of accumulated other comprehensive income (loss) for Great Plains Energy and KCP&L.



Great Plains Energy
	Gains and Losses on Cash Flow Hedges^(a)				Defined Benefit Pension Items^(a)				Total^(a)
	(millions)
2017
Beginning balance January 1		$	(4.5	)		$	(2.1	)	$	(6.6	)
Other comprehensive loss before reclassification		—				(0.9		)	(0.9		)
Amounts reclassified from accumulated other comprehensive loss		4.9				0.4			5.3
Net current period other comprehensive income (loss)		4.9				(0.5		)	4.4
Ending balance December 31		$	0.4			$	(2.6	)	$	(2.2	)
2016
Beginning balance January 1		$	(10.1	)		$	(1.9	)	$	(12.0	)
Other comprehensive loss before reclassifications		—				(0.7		)	(0.7		)
Amounts reclassified from accumulated other comprehensive loss		5.6				0.5			6.1
Net current period other comprehensive income (loss)		5.6				(0.2		)	5.4
Ending balance December 31		$	(4.5	)		$	(2.1	)	$	(6.6	)

^(a) Net of tax



KCP&L
	Gains and Losses on Cash Flow Hedges^(a)
	(millions)
2017
Beginning balance January 1		$	(4.2	)
Amounts reclassified from accumulated other comprehensive loss		4.6
Net current period other comprehensive income		4.6
Ending balance December 31		$	0.4
2016
Beginning balance January 1		$	(9.6	)
Amounts reclassified from accumulated other comprehensive loss		5.4
Net current period other comprehensive income		5.4
Ending balance December 31		$	(4.2	)

^(a) Net of tax

The following tables reflect the effect on certain line items of net income from amounts reclassified out of each component of accumulated other comprehensive income (loss) for Great Plains Energy and KCP&L.



Great Plains Energy
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
	2017			2016
	(millions)
Gains (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(7.9	)	$	(9.2	)	Interest charges
	(7.9		)	(9.2		)	Income before income tax expense and income from equity investments
	3.0			3.6			Income tax benefit
	$	(4.9	)	$	(5.6	)	Net income (loss)
Amortization of defined benefit pension items
Net losses included in net periodic benefit costs	$	(0.7	)	$	(0.8	)	Utility operating and maintenance expenses
	(0.7		)	(0.8		)	Income before income tax expense and income from equity investments
	0.3			0.3			Income tax benefit
	$	(0.4	)	$	(0.5	)	Net income (loss)

Total reclassifications, net of tax	$	(5.3	)	$	(6.1	)	Net income (loss)



KCP&L
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Income (Loss)						Affected Line Item in the Income Statement
	2017			2016
	(millions)
Gains (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(7.5	)	$	(8.8	)	Interest charges
	(7.5		)	(8.8		)	Income before income tax expense
	2.9			3.4			Income tax benefit
Total reclassifications, net of tax	$	(4.6	)	$	(5.4	)	Net income

Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Tax Disclosure [Text Block]

21. TAXES

Components of income tax expense are detailed in the following tables.



Great Plains Energy	2017			2016			2015
Current income taxes	(millions)
Federal	$	(1.7	)	$	0.3		$	(0.2	)
State	1.0			0.7			(1.1		)
Total	(0.7		)	1.0			(1.3		)
Deferred income taxes
Federal	223.5			140.6			96.9
State	11.9			29.5			28.0
Total	235.4			170.1			124.9
Investment tax credit
Deferral	—			2.5			0.5
Amortization	(1.4		)	(1.4		)	(1.4		)
Total	(1.4		)	1.1			(0.9		)
Income tax expense	$	233.3		$	172.2		$	122.7

Great Plains Energy's 2017 federal deferred income tax expense includes $130.3 million of additional income tax expense due to the impacts of U.S. federal income tax reform, discussed further below.



KCP&L	2017			2016			2015
Current income taxes	(millions)
Federal	$	37.4		$	24.8		$	(18.7	)
State	8.3			4.7			(3.4		)
Total	45.7			29.5			(22.1		)
Deferred income taxes
Federal	74.7			76.4			81.9
State	8.8			17.0			17.5
Total	83.5			93.4			99.4
Investment tax credit
Deferral	—			—			0.5
Amortization	(1.0		)	(1.0		)	(1.0		)
Total	(1.0		)	(1.0		)	(0.5		)
Income tax expense	$	128.2		$	121.9		$	76.8

Effective Income Tax Rates

Effective income tax rates reflected in the financial statements and the reasons for their differences from the statutory federal rates are detailed in the following tables.



Great Plains Energy	2017		2016		2015
Federal statutory income tax rate	35.0	%	35.0	%	35.0	%
Differences between book and tax depreciation not normalized	0.1		(0.1	)	—
Amortization of investment tax credits	(1.1	)	(0.3	)	(0.4	)
Federal income tax credits	(5.8	)	(2.6	)	(4.1	)
State income taxes	8.3		4.2		4.0
Transaction-related costs	42.5		0.9		—
Valuation allowance	8.9		—		1.5
Federal tax rate change	95.3		—		—
Other	0.3		0.2		0.5
Effective income tax rate	183.5	%	37.3	%	36.5	%

The increase in Great Plains Energy's effective income tax rate for 2017 is driven by significant transaction-related costs incurred in connection with the anticipated merger with Westar that are not deductible for tax purposes and the impacts of U.S. federal income tax reform, discussed further below.



KCP&L	2017		2016		2015
Federal statutory income tax rate	35.0	%	35.0	%	35.0	%
Differences between book and tax depreciation not normalized	(0.1	)	(0.3	)	—
Amortization of investment tax credits	(0.3	)	(0.3	)	(0.5	)
Federal income tax credits	(2.4	)	(3.1	)	(5.6	)
State income taxes	3.8		4.1		4.0
Valuation allowance	0.4		—		0.3
Federal tax rate change	5.3		—		—
Other	(0.1	)	(0.2	)	0.3
Effective income tax rate	41.6	%	35.2	%	33.5	%

Deferred Income Taxes

The tax effects of major temporary differences resulting in deferred income tax assets (liabilities) in the consolidated balance sheets are in the following tables.



	Great Plains Energy						KCP&L
December 31	2017			2016			2017			2016
Noncurrent deferred income taxes	(millions)
Plant related	$	(1,549.0	)	$	(2,107.6	)	$	(1,114.9	)	$	(1,492.2	)
Income taxes on future regulatory refunds (recoveries)	236.0			(148.7		)	179.1			(123.9		)
Derivative instruments	(19.2		)	(17.0		)	1.6			8.5
Pension and post-retirement benefits	9.4			10.5			28.6			38.6
SO₂emission allowance sales	14.9			24.1			15.0			24.1
Fuel recovery mechanisms	(17.9		)	(22.3		)	(15.9		)	(27.2		)
Tax credit carryforwards	279.8			271.1			185.8			177.4
Customer demand programs	(17.4		)	(34.3		)	(11.7		)	(21.8		)
Solar rebates	(15.2		)	(27.3		)	(5.8		)	(11.4		)
Net operating loss carryforward	473.0			718.0			131.2			198.3
Other	6.9			20.2			(9.1		)	1.3
Net noncurrent deferred income tax liability before valuation allowance	(598.7		)	(1,313.3		)	(616.1		)	(1,228.3		)
Valuation allowance	(23.0		)	(16.4		)	—			—
Net noncurrent deferred income tax liability	$	(621.7	)	$	(1,329.7	)	$	(616.1	)	$	(1,228.3	)



	Great Plains Energy						KCP&L
December 31	2017			2016			2017			2016
	(millions)
Gross deferred income tax assets	$	2,017.4		$	1,360.9		$	1,261.5		$	747.7
Gross deferred income tax liabilities	(2,639.1		)	(2,690.6		)	(1,877.6		)	(1,976.0		)
Net deferred income tax liability	$	(621.7	)	$	(1,329.7	)	$	(616.1	)	$	(1,228.3	)

Tax Credit Carryforwards

At December 31, 2017 and 2016, Great Plains Energy had $191.0 million and $183.5 million, respectively, of federal general business income tax credit carryforwards. At December 31, 2017 and 2016, KCP&L had $184.6 million and $177.4 million, respectively, of federal general business income tax credit carryforwards. The carryforwards for both Great Plains Energy and KCP&L relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits and expire in the years 2028 to 2037. Approximately $0.5 million of Great Plains Energy's credits are related to Low Income Housing credits that were acquired in the GMO acquisition. Due to federal limitations on the utilization of income tax attributes acquired in the GMO acquisition, management expects a portion of these credits to expire unutilized and has provided a valuation allowance against $0.4 million of the federal income tax benefit.

At December 31, 2017 and 2016, Great Plains Energy had $87.6 million of federal alternative minimum tax credit carryforwards, all of which were acquired in the GMO acquisition. These credits do not expire and can be used to reduce taxes paid in the future or become refundable starting in 2018. Due to potential federal budget sequestration reductions for refundable income tax credits, management expects a portion of these credits will not be refunded and has provided a valuation allowance against $5.8 million of the federal income tax benefit.

At December 31, 2017, Great Plains Energy and KCP&L had $1.2 million of state income tax credit carryforwards. The state income tax credits relate primarily to the Company's Kansas research and development tax credits, which do not expire.

Net Operating Loss Carryforwards

At December 31, 2017 and 2016, Great Plains Energy had $382.0 million and $643.8 million, respectively, of tax benefits related to federal net operating loss (NOL) carryforwards. Approximately $179.3 million and $306.2 million at December 31, 2017 and 2016, respectively, are tax benefits related to NOLs that were acquired in the GMO acquisition. The federal NOL carryforwards expire in years 2023 to 2036. The year of origin of Great Plains Energy's related tax benefit amounts for federal NOL carryforwards as of December 31, 2017 are detailed in the following table.



	Amount of
Year of Origin	Benefit
	(millions)
2003	$	9.5
2004	91.4
2005	44.4
2006	32.0
2007	0.8
2008	1.4
2009	21.9
2010	2.5
2011	65.3
2012	0.2
2013	0.8
2014	52.0
2015	59.2
2016	0.6
	$	382.0

In addition, Great Plains Energy also had deferred tax benefits of $91.0 million and $74.2 million related to state NOLs as of December 31, 2017 and 2016, respectively. Of these amounts, approximately $42.1 million and $36.1 million at December 31, 2017 and 2016, respectively, were acquired in the GMO acquisition. Management does not expect to utilize $16.8 million of NOLs before the expiration date of the carryforwards of NOLs in certain states. Therefore, a valuation allowance has been provided against $16.8 million of state tax benefits.

Valuation Allowances

Great Plains Energy is required to assess the ultimate realization of deferred tax assets using a “more likely than not” assessment threshold. This assessment takes into consideration tax planning strategies within Great Plains Energy's control. As a result of this assessment, Great Plains Energy has established a partial valuation allowance for state tax NOL carryforwards and tax credit carryforwards. During 2017, $6.6 million of tax expense was recorded in continuing operations primarily related to a reduction in the refundable portion of federal Alternative Minimum Tax (AMT) credits.

Tax Reform

In December 2017, the U.S. Congress passed and President Donald Trump signed Public Law No. 115-97, commonly referred to as the Tax Cuts and Jobs Act (Tax Act). The Tax Act represents the first major reform in U.S. income tax law since 1986. Most notably, the Tax Act reduces the current top corporate income tax rate from 35% to 21% beginning in 2018, repeals the corporate AMT, makes existing AMT tax credit carryforwards refundable, and changes the deductibility and taxability of certain items, among other things.

In December 2017, the SEC staff issued Staff Accounting Bulletin (SAB) 118, which provides guidance on accounting for the tax effects of the Tax Act. SAB 118 provides a measurement period that should not extend beyond one year from the Tax Act enactment date for companies to complete the accounting under ASC 740, Income Taxes. In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Tax Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate to be included in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the enactment of the Tax Act. Great Plains Energy’s and KCP&L’s accounting for the Tax Act under ASC 740 as of December 31, 2017 is complete and is detailed further below.

As a result of the change in the corporate income tax rate, Great Plains Energy and KCP&L revalued and restated their deferred income tax assets and liabilities in December 2017. Great Plains Energy decreased its net deferred income tax liabilities by $814.5 million, primarily consisting of a $645.5 million adjustment for the revaluation and restatement of deferred income tax assets and liabilities included in rate base and a $222.8 million tax gross-up adjustment for ratemaking purposes. KCP&L decreased its net deferred income tax liabilities by $682.8 million, primarily consisting of a $471.8 million adjustment for the revaluation and restatement of deferred income tax assets and liabilities included in rate base and a $163.6 million tax gross-up adjustment for ratemaking purposes. The decreases to Great Plains Energy's and KCP&L's net deferred income tax liabilities included in rate base were offset by a corresponding increase in regulatory liabilities. The net regulatory liabilities will be refunded to customers in future rates by amortizing the amounts related to plant assets over the remaining useful life of the assets, and amortizing the amounts related to other items over a period to be determined in a future rate case.

Great Plains Energy recognized $130.3 million of income tax expense consisting of $110.1 million primarily related to the revaluation of GMO’s non-regulated deferred income tax assets, $9.1 million related to the reassessment of the valuation allowance needed for the realization of refundable AMT credits and state NOLs and $11.1 million related to KCP&L and GMO deferred income taxes not included in rate base. KCP&L recognized $16.5 million of income tax expense related to deferred income taxes not included in rate base.

KCP&L and GMO currently recover the cost of income taxes in rates from their customers based on the 35% federal corporate income tax rate. Both KCP&L and GMO have announced their intentions to pass the income tax savings generated by the tax rate change, currently estimated at approximately $100 million annually, through to customers as part of upcoming general rate cases, including applications filed by KCP&L and GMO in Missouri in January 2018. However, both the MPSC and KCC have also initiated investigatory dockets regarding the impact of the Tax Act on customer rates and the actual rate treatment of tax reform will not be known until orders specifying that treatment are received from the MPSC and KCC. In January 2018, KCC issued an order requiring certain regulated public utilities, including KCP&L, to begin recording a regulatory liability for the difference between the new corporate tax rate and amounts currently collected in rates. The treatment of the regulatory liability will be addressed by KCC in future orders.

Segments and Related Information

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Segments and Related Information

22. SEGMENTS AND RELATED INFORMATION

Great Plains Energy has one reportable segment based on its method of internal reporting, which segregates reportable segments based on products and services, management responsibility and regulation. The one reportable business segment is Electric Utility, consisting of KCP&L, GMO's regulated utility operations and GMO Receivables Company. Other includes GMO activity other than its regulated utility operations, GPETHC and unallocated corporate charges, including certain costs to achieve the anticipated merger with Westar. The summary of significant accounting policies applies to the reportable segment. Segment performance is evaluated based on net income (loss).

The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment.



2017	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,708.2			$	—			$	—		$	2,708.2
Depreciation and amortization		(371.1		)		—				—			(371.1		)
Interest charges		(196.9		)		(125.9		)		32.1			(290.7		)
Income tax expense		(169.4		)		(63.9		)		—			(233.3		)
Net income (loss)		256.9				(363.1		)		—			(106.2		)



2016	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,676.0			$	—			$	—		$	2,676.0
Depreciation and amortization		(344.8		)		—				—			(344.8		)
Interest charges		(196.1		)		2.5				32.1			(161.5		)
Income tax expense		(164.3		)		(7.9		)		—			(172.2		)
Net income (loss)		292.1				(2.1		)		—			290.0



2015	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,502.2			$	—			$	—		$	2,502.2
Depreciation and amortization		(330.4		)		—				—			(330.4		)
Interest charges		(190.9		)		(40.5		)		32.1			(199.3		)
Income tax expense		(120.8		)		(1.9		)		—			(122.7		)
Net income (loss)		223.8				(10.8		)		—			213.0



	Electric Utility			Other				Eliminations				Great Plains Energy
2017		(millions)
Assets		$	11,508.1		$	1,285.7			$	(335.9	)		$	12,457.9
Capital expenditures		573.5			—				—				573.5
2016
Assets		$	11,444.2		$	2,461.3			$	(335.5	)		$	13,570.0
Capital expenditures		609.4			—				—				609.4
2015
Assets		$	11,045.5		$	(51.1	)		$	(255.8	)		$	10,738.6
Capital expenditures		677.1			—				—				677.1

Jointly Owned Electric Utility Plants

12 Months Ended

Dec. 31, 2017

Jointly Owned Electric Utility Plants [Abstract]

Jointly Owned Electric Utility Plants [Text Block]

23. JOINTLY-OWNED ELECTRIC UTILITY PLANTS

Great Plains Energy's and KCP&L's share of jointly-owned electric utility plants at December 31, 2017, are detailed in the following tables.



Great Plains Energy
	Wolf Creek Unit			La Cygne Units			Iatan No. 1 Unit			Iatan No. 2 Unit			Iatan Common			Jeffrey Energy Center
	(millions, except MW amounts)
Great Plains Energy's share		47%			50%			88%			73%			79%			8%

Utility plant in service		$	1,854.2		$	1,191.1		$	699.9		$	1,355.8		$	491.1		$	201.1
Accumulated depreciation		918.1			347.8			280.8			413.0			130.7			82.0
Nuclear fuel, net		72.4			—			—			—			—			—
Construction work in progress		91.8			8.6			31.8			35.0			21.7			2.5
2018 accredited capacity-MWs		552			699			616			641			NA			173



KCP&L
	Wolf Creek Unit			La Cygne Units			Iatan No. 1 Unit			Iatan No. 2 Unit			Iatan Common
	(millions, except MW amounts)
KCP&L's share		47%			50%			70%			55%			61%

Utility plant in service		$	1,854.2		$	1,191.1		$	561.7		$	1,041.6		$	401.8
Accumulated depreciation		918.1			347.8			228.9			366.6			117.5
Nuclear fuel, net		72.4			—			—			—			—
Construction work in progress		91.8			8.6			7.6			14.8			12.0
2018 accredited capacity-MWs		552			699			490			482			NA

Each owner must fund its own portion of the plant's operating expenses and capital expenditures. KCP&L's and GMO's share of direct expenses are included in the appropriate operating expense classifications in Great Plains Energy's and KCP&L's financial statements.

Quarterly Operating Results (Unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information [Text Block]

24. QUARTERLY OPERATING RESULTS (UNAUDITED)



	Quarter
Great Plains Energy	1st			2nd			3rd		4th
2017	(millions, except per share amounts)
Operating revenue	$	570.7		$	682.6		$	857.2	$	597.7
Operating income	47.4			176.5			305.9		73.8
Net income (loss)	(9.6		)	(7.0		)	10.5		(100.1		)
Basic and diluted earnings (loss) per common share	(0.11		)	(0.10		)	0.02		(0.46		)
2016
Operating revenue	$	572.1		$	670.8		$	856.8	$	576.3
Operating income	89.9			182.3			281.9		64.8
Net income	26.4			32.0			133.6		98.0
Basic and diluted earnings per common share	0.17			0.20			0.86		0.39



	Quarter
KCP&L	1st		2nd		3rd		4th
2017	(millions)
Operating revenue	$	395.9	$	482.7	$	595.7	$	416.4
Operating income	58.2		113.8		209.9		61.8
Net income	14.2		49.6		114.1		1.9
2016
Operating revenue	$	400.9	$	475.6	$	597.6	$	401.3
Operating income	70.6		137.9		219.2		54.4
Net income	24.6		65.9		117.7		16.8

In the fourth quarter of 2017, Great Plains Energy recorded $130.3 million of additional income tax expense due to the impacts of U.S. federal income tax reform. See Note 21 for additional information regarding the impact of tax reform on Great Plains Energy.

Quarterly data is subject to seasonal fluctuations with peak periods occurring in the summer months.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Organization [Policy Text Block]

Organization


•	KCP&L is an integrated, regulated electric utility that provides electricity to customers primarily in the states of Missouri and Kansas. KCP&L has one active wholly owned subsidiary, Kansas City Power & Light Receivables Company (KCP&L Receivables Company).

•

Each of Great Plains Energy's and KCP&L's consolidated financial statements includes the accounts of their subsidiaries. Intercompany transactions have been eliminated.

Great Plains Energy's sole reportable business segment is the electric utility segment (Electric Utility). See Note 22 for additional information.

Use of Estimates, Policy [Policy Text Block]

Use of Estimates

Cash and Cash Equivalents, Policy [Policy Text Block]

Cash and Cash Equivalents

Cash equivalents consist of highly liquid investments with original maturities of three months or less at acquisition.

Time Deposit, Policy [Policy Text Block]

Time Deposit

Fair Value of Financial Instruments, Policy [Policy Text Block]

Fair Value of Financial Instruments

The following methods and assumptions were used to estimate the fair value of each class of financial instrument for which it is practicable to estimate that value.

Derivatives, Policy [Policy Text Block]

Derivative Instruments

Utility Plant, Policy [Policy Text Block]

Utility Plant

Depreciation and Amortization, Policy [Policy Text Block]

Depreciation and Amortization

Nuclear Plant Decommissioning Costs, Policy [Policy Text Block]

Nuclear Plant Decommissioning Costs

Deferred Refueling Outage Costs, Policy [Policy Text Block]

Deferred Refueling Outage Costs

Regulatory Matters, Policy [Policy Text Block]

Regulatory Matters

Revenue Recognition, Policy [Policy Text Block]

Revenue Recognition

Allowance for Doubtful Accounts, Policy [Policy Text Block]

Allowance for Doubtful Accounts

Property Gains And Losses, Policy [Policy Text Block]

Property Gains and Losses

Net gains and losses from the sale of assets and businesses and from asset impairments are recorded in operating expenses.

Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]

Asset Impairments

Income Taxes, Policy [Policy Text Block]

Income Taxes

Environmental Matters, Policy [Policy Text Block]

Environmental Matters

Environmental costs are accrued when it is probable a liability has been incurred and the amount of the liability can be reasonably estimated.

Basic and Diluted Earnings per Common Share Calculation [Policy Text Block]

Basic and Diluted Earnings (Loss) per Common Share Calculation

New Accounting Pronouncements, Policy [Policy Text Block]

New Accounting Standards

Plant Retirement and Abandonment, Policy [Policy Text Block]

Plant to be Retired, Net

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of Public Utility Property, Plant, and Equipment [Table Text Block]

Great Plains Energy's and KCP&L's balances of utility plant, at original cost, with a range of estimated useful lives are listed in the following tables.



Great Plains Energy
December 31	2017		2016
Utility plant, at original cost	(millions)
Generation (20 - 60 years)	$	7,930.8	$	8,106.4
Transmission (15 - 70 years)	912.3		886.3
Distribution (8 - 66 years)	3,789.0		3,629.1
General (5 - 50 years)	1,042.0		975.9
Total ^(a)	$	13,674.1	$	13,597.7

Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]

The following table reconciles Great Plains Energy's basic and diluted EPS.



	2017			2016		2015
	(millions, except per share amounts)
Income (Loss)
Net income (loss)	$	(106.2	)	$	290.0	$	213.0
Less: preferred stock dividend requirements and redemption premium	37.3			16.5		1.6
Earnings (loss) available for common shareholders	$	(143.5	)	$	273.5	$	211.4
Common Shares Outstanding
Average number of common shares outstanding	215.5			169.4		154.2
Add: effect of dilutive securities	—			0.4		0.6
Diluted average number of common shares outstanding	215.5			169.8		154.8
Basic and Diluted EPS	$	(0.67	)	$	1.61	$	1.37

Supplemental Cash Flow Information (Tables)

12 Months Ended

Dec. 31, 2017

Supplemental Cash Flow Elements [Abstract]

Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]



Great Plains Energy Other Operating Activities
Year Ended December 31	2017			2016			2015
Cash flows affected by changes in:	(millions)
Receivables	$	14.8		$	(18.3	)	$	12.5
Accounts receivable pledged as collateral	(7.6		)	2.6			(4.0		)
Fuel inventories	5.6			9.6			(28.3		)
Materials and supplies	(9.0		)	(6.5		)	(3.0		)
Accounts payable	9.0			(25.4		)	(11.4		)
Accrued taxes	1.5			8.1			1.1
Accrued interest	(8.0		)	6.1			3.4
Deferred refueling outage costs	15.5			(3.1		)	(6.7		)
Pension and post-retirement benefit obligations	26.1			27.4			18.5
Allowance for equity funds used during construction	(6.0		)	(6.6		)	(4.8		)
Fuel recovery mechanisms	(11.4		)	(46.9		)	47.5
ARO settlements	(28.5		)	(17.4		)	(4.1		)
Other	20.6			28.1			(7.8		)
Total other operating activities	$	22.6		$	(42.3	)	$	12.9
Cash paid during the period:
Interest	$	258.9		$	191.2		$	182.2
Income taxes	$	—		$	0.1		$	0.1
Non-cash investing activities:
Liabilities accrued for capital expenditures	$	39.8		$	32.4		$	35.7



KCP&L Other Operating Activities
Year Ended December 31	2017			2016			2015
Cash flows affected by changes in:	(millions)
Receivables	$	13.8		$	(12.4	)	$	2.6
Accounts receivable pledged as collateral	(20.0		)	—			—
Fuel inventories	1.9			10.6			(24.7		)
Materials and supplies	(7.1		)	(4.3		)	(4.5		)
Accounts payable	11.7			(30.5		)	(18.0		)
Accrued taxes	9.1			67.9			(19.0		)
Accrued interest	—			—			3.4
Deferred refueling outage costs	15.5			(3.1		)	(6.7		)
Pension and post-retirement benefit obligations	27.3			28.6			18.4
Allowance for equity funds used during construction	(6.0		)	(6.6		)	(3.8		)
Fuel recovery mechanisms	8.3			(53.7		)	3.5
ARO settlements	(25.5		)	(15.0		)	(4.1		)
Other	(9.0		)	16.4			(8.6		)
Total other operating activities	$	20.0		$	(2.1	)	$	(61.5	)
Cash paid during the period:
Interest	$	128.0		$	127.0		$	120.2
Income taxes	$	38.8		$	—		$	—
Non-cash investing activities:
Liabilities accrued for capital expenditures	$	32.9		$	27.2		$	23.9

Receivables (Tables)

12 Months Ended

Dec. 31, 2017

Receivables [Abstract]

Schedule of receivables [Table Text Block]

Great Plains Energy's and KCP&L's receivables are detailed in the following table.



	December 31
		2017			2016
Great Plains Energy		(millions)
Customer accounts receivable - billed		$	3.7		$	26.2
Customer accounts receivable - unbilled		103.2			79.1
Allowance for doubtful accounts - customer accounts receivable		(4.7		)	(4.0		)
Other receivables		49.5			64.7
Total		$	151.7		$	166.0
KCP&L
Customer accounts receivable - billed		$	1.6		$	25.5
Customer accounts receivable - unbilled		67.6			63.7
Allowance for doubtful accounts - customer accounts receivable		(2.2		)	(1.8		)
Other receivables		39.3			51.7
Total		$	106.3		$	139.1

Nuclear Plant (Tables)

12 Months Ended

Dec. 31, 2017

Nuclear Plant [Abstract]

Changes in nuclear decommissioning trust fund

The following table summarizes the change in Great Plains Energy's and KCP&L's nuclear decommissioning trust fund.



	2017			2016
Decommissioning Trust		(millions)
Beginning balance January 1		$	222.9		$	200.7
Contributions		3.3			3.3
Earned income, net of fees		4.3			4.1
Net realized gains		0.7			0.3
Net unrealized gains		27.2			14.5
Ending balance December 31		$	258.4		$	222.9

Detail of assets held in nuclear decommissioning trust fund

The nuclear decommissioning trust is reported at fair value on the balance sheets and is invested in assets as detailed in the following table.



	December 31
	2017												2016
	Cost Basis		Unrealized Gains			Unrealized Losses				Fair Value			Cost Basis			Unrealized Gains			Unrealized Losses				Fair Value
	(millions)
Equity securities	$	96.5		$	88.3		$	(1.0	)		$	183.8		$	93.3		$	62.1		$	(1.5	)		$	153.9
Debt securities	69.7			2.7			(0.4		)		72.0			63.4			2.3			(0.5		)		65.2
Other	2.6			—			—				2.6			3.8			—			—				3.8
Total	$	168.8		$	91.0		$	(1.4	)		$	258.4		$	160.5		$	64.4		$	(2.0	)		$	222.9

Gains and losses from the sale of securities by the nuclear decommissioning trust fund

The following table summarizes the realized gains and losses from the sale of securities in the nuclear decommissioning trust fund.



	2017			2016			2015
	(millions)
Realized gains	$	2.5		$	1.6		$	5.3
Realized losses	(1.8		)	(1.3		)	(4.6		)

Nuclear plant decommissioning costs [Table Text Block]



		KCC			MPSC
	(millions)
Current cost of decommissioning (in 2017 dollars)
Total Station		$	813.7		$	813.7
KCP&L's 47% Share		382.5			382.5

Future cost of decommissioning (in 2045-2053 dollars) ^(a)
Total Station		$	1,982.4		$	2,137.8
KCP&L's 47% Share		931.7			1,004.8

Annual escalation factor		2.91		%	3.16		%
Annual return on trust assets ^(b)		5.64		%	5.46		%

^(a)Total future cost over an eight year decommissioning period

Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2017

Regulated Operations [Abstract]

Schedule Of Regulatory Assets And Liabilities [Table Text Block]

Great Plains Energy's and KCP&L's regulatory assets and liabilities are detailed in the following table.



	December 31
	2017								2016
	KCP&L			GMO			Great Plains Energy		KCP&L		GMO		Great Plains Energy
Regulatory Assets	(millions)
Taxes recoverable through future rates	$	—		$	—		$	—	$	123.9	$	24.8	$	148.7
Loss on reacquired debt	8.7		^(a)	1.2		^(a)	9.9		10.0		1.7		11.7
Cost of removal	30.3			—			30.3		28.6		—		28.6
Asset retirement obligations	94.3			24.2			118.5		69.6		24.9		94.5
Pension and post-retirement costs	379.7		^(b)	108.2		^(b)	487.9		367.9		104.7		472.6
Deferred customer programs	40.9		^(c)	19.4		^(d)	60.3		45.9		27.4		73.3
Fuel recovery mechanism	61.7		^(e)	12.0		^(e)	73.7		69.9		—		69.9
Iatan No. 1 and common facilities depreciation and carrying costs	12.9		^(f)	4.7		^(g)	17.6		13.6		5.0		18.6
Iatan No. 2 construction accounting costs	25.0		^(h)	13.7		^(h)	38.7		26.9		16.1		43.0
Kansas property tax surcharge	6.6		^(e)	—			6.6		3.6		—		3.6
Solar rebates	22.6		⁽ⁱ⁾	37.0		^(e)	59.6		29.2		41.6		70.8
Transmission delivery charge	3.2		^(e)	—			3.2		3.1		—		3.1
La Cygne deferred depreciation	2.7		^(j)	—			2.7		2.8		—		2.8
Other	3.3		^(e)	1.6			4.9		6.8		—		6.8
Total	$	691.9		$	222.0		$	913.9	$	801.8	$	246.2	$	1,048.0
Regulatory Liabilities
Taxes refundable through future rates	$	574.0		$	220.6		$	794.6	$	—	$	—	$	—
Emission allowances	58.1			—			58.1		62.1		—		62.1
Asset retirement obligations	126.0			—			126.0		99.7		—		99.7
Cost of removal	—			57.4			57.4		—		65.1		65.1
Fuel recovery mechanism	—			3.9			3.9		—		11.6		11.6
Pension and post-retirement costs	12.0			8.2			20.2		15.3		7.4		22.7
Other	9.1			37.0			46.1		10.3		38.4		48.7
Total	$	779.2		$	327.1		$	1,106.3	$	187.4	$	122.5	$	309.9

^(a)Amortized over the life of the related new debt issuances or the remaining lives of the old debt issuances if no new debt was issued.

^(c) $16.1 million not included in rate base and amortized over various periods.

^(d)$10.9 million not included in rate base and amortized over various periods.

^(e)Not included in rate base and amortized over various periods.

^(f)Included in rate base and amortized over various periods.


^(g)	Included in rate base and amortized through 2038.

^(h)Included in rate base and amortized through 2059.

⁽ⁱ⁾Not included in rate base and amortized through 2020.

^(j)Included in rate base and amortized through 2040.

Goodwill and Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2017

Finite-Lived Intangible Assets [Line Items]

Schedule of Finite-Lived Intangible Assets [Table Text Block]

Great Plains Energy's and KCP&L's intangible assets are included in electric utility plant on the consolidated balance sheets and are detailed in the following table.



	December 31
		2017							2016
	Gross Carrying Amount			Accumulated Amortization				Gross Carrying Amount			Accumulated Amortization
Great Plains Energy	(millions)
Computer software		$	386.8		$	(251.2	)		$	355.2		$	(219.1	)
Asset improvements		30.3			(8.0		)		28.8			(6.7		)

KCP&L
Computer software		$	368.7		$	(234.3	)		$	338.3		$	(203.1	)
Asset improvements		15.1			(2.7		)		13.6			(1.8		)

Amortization Expense Related to Intangible Assets [Table Text Block]

Great Plains Energy's and KCP&L's amortization expense related to intangible assets is detailed in the following table.



	2017		2016
	(millions)
Great Plains Energy	$	33.7	$	29.1
KCP&L	32.1		25.7

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]



	2018		2019		2020		2021		2022
	(millions)
Great Plains Energy	$	30.5	$	25.7	$	24.5	$	20.0	$	14.9
KCP&L	29.7		25.0		23.8		19.5		14.5

Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2017

Asset Retirement Obligation Disclosure [Abstract]

Schedule of Change in Asset Retirement Obligation [Table Text Block]

The following table summarizes the change in Great Plains Energy's and KCP&L's AROs.



	Great Plains Energy						KCP&L
	2017			2016			2017			2016
	(millions)
Beginning balance	$	316.0		$	275.9		$	278.0		$	239.3
Additions	—			1.6			—			1.3
Revision in timing and/or estimates	(1.3		)	42.1			0.3			40.1
Settlements	(28.5		)	(17.4		)	(25.5		)	(15.0		)
Accretion	14.9			13.8			13.5			12.3
Total	$	301.1		$	316.0		$	266.3		$	278.0
Less: current portion	(38.6		)	—			(34.9		)	—
Total noncurrent asset retirement obligation	$	262.5		$	316.0		$	231.4		$	278.0

Pension Plans and Other Employee Benefits (Tables)

12 Months Ended

Dec. 31, 2017

Defined Benefit Plan Disclosure [Line Items]

Schedule of Net Benefit Costs [Table Text Block]



	Pension Benefits									Other Benefits
	2017			2016			2015			2017			2016			2015
Components of net periodic benefit costs	(millions)
Service cost	$	44.2		$	42.0		$	45.3		$	2.1		$	2.6		$	3.3
Interest cost	53.5			52.9			50.3			5.4			6.1			6.8
Expected return on plan assets	(51.2		)	(49.2		)	(51.7		)	(2.6		)	(3.1		)	(2.9		)
Prior service cost	0.7			0.7			0.8			—			1.2			3.1
Recognized net actuarial (gain) loss	49.7			51.8			51.4			(0.5		)	(1.5		)	0.2
Transition obligation	—			—			—			—			—			0.2
Settlement and special termination benefits	16.3			—			—			—			—			—
Net periodic benefit costs before regulatory adjustment	113.2			98.2			96.1			4.4			5.3			10.7
Regulatory adjustment	(13.8		)	(4.9		)	(9.8		)	1.9			6.0			4.4
Net periodic benefit costs	99.4			93.3			86.3			6.3			11.3			15.1
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Current year net (gain) loss	72.0			63.6			8.6			3.0			1.1			(20.6		)
Amortization of gain (loss)	(65.6		)	(51.8		)	(51.4		)	0.5			1.5			(0.2		)
Prior service cost	—			—			—			—			(10.2		)	(7.0		)
Amortization of prior service cost	(0.7		)	(0.7		)	(0.8		)	—			(1.2		)	(3.1		)
Amortization of transition obligation	—			—			—			—			—			(0.2		)
Other regulatory activity	9.6			4.6			4.3			(1.0		)	(5.4		)	(4.4		)
Total recognized in OCI or regulatory asset/liability	15.3			15.7			(39.3		)	2.5			(14.2		)	(35.5		)
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	$	114.7		$	109.0		$	47.0		$	8.8		$	(2.9	)	$	(20.4	)

Schedule of Net Funded Status [Table Text Block]



	Pension Benefits						Other Benefits
	2017			2016			2017			2016
Change in projected benefit obligation (PBO)	(millions)
PBO at January 1	$	1,244.6		$	1,154.8		$	130.1		$	137.5
Service cost	44.2			42.0			2.1			2.6
Interest cost	53.5			52.9			5.4			6.1
Contribution by participants	—			—			6.0			5.3
Amendments	—			—			—			(10.1		)
Actuarial (gain) loss	135.6			65.5			2.1			0.6
Benefits paid	(36.8		)	(70.6		)	(12.5		)	(11.9		)
Settlements and special termination benefits	(85.2		)	—			—			—
PBO at December 31	$	1,355.9		$	1,244.6		$	133.2		$	130.1
Change in plan assets
Fair value of plan assets at January 1	$	776.8		$	723.9		$	115.6		$	114.3
Actual return on plan assets	114.8			51.1			1.8			2.6
Contributions by employer and participants	76.9			69.8			10.4			10.2
Benefits paid	(34.5		)	(68.0		)	(12.0		)	(11.5		)
Settlements	(85.6		)	—			—			—
Fair value of plan assets at December 31	$	848.4		$	776.8		$	115.8		$	115.6
Funded status at December 31	$	(507.5	)	$	(467.8	)	$	(17.4	)	$	(14.5	)
Amounts recognized in the consolidated balance sheets
Non-current asset	$	—		$	—		$	12.8		$	9.0
Current pension and other post-retirement liability	(1.9		)	(2.2		)	(0.8		)	(0.8		)
Noncurrent pension liability and other post-retirement liability	(505.6		)	(465.6		)	(29.4		)	(22.7		)
Net amount recognized before regulatory treatment	(507.5		)	(467.8		)	(17.4		)	(14.5		)
Accumulated OCI or regulatory asset/liability	492.2			476.9			(21.1		)	(23.6		)
Net amount recognized at December 31	$	(15.3	)	$	9.1		$	(38.5	)	$	(38.1	)
Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost:
Actuarial (gain) loss	$	248.9		$	242.5		$	2.8		$	(0.7	)
Prior service cost	2.5			3.2			(8.0		)	(8.0		)
Other	240.8			231.2			(15.9		)	(14.9		)
Net amount recognized at December 31	$	492.2		$	476.9		$	(21.1	)	$	(23.6	)

Schedule Of Periodic Benefit Obligation And Accumulated Benefit Obligation And Fair Value Of Plan Assets By Funded And Under Funded Plans [Table Text Block]



	2017		2016
Pension plans with the PBO in excess of plan assets	(millions)
Projected benefit obligation	$	1,355.9	$	1,244.6
Fair value of plan assets	848.4		776.8
Pension plans with the ABO in excess of plan assets
Accumulated benefit obligation	$	1,169.8	$	1,090.2
Fair value of plan assets	848.4		776.8
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated other post-retirement benefit obligation	$	111.6	$	61.7
Fair value of plan assets	81.5		38.3

Schedule of Expected Benefit Payments [Table Text Block]



	Pension Benefits		Other Benefits
	(millions)
2018	$	79.3	$	9.2
2019	82.2		9.2
2020	84.7		9.6
2021	86.0		10.1
2022	86.5		10.4
2023-2027	459.9		55.6

Schedule of Assumptions Used [Table Text Block]



Weighted-average assumptions used to determine the benefit obligation at December 31	Pension Benefits				Other Benefits
	2017		2016		2017		2016
Discount rate	3.72	%	4.31	%	3.64	%	4.20	%
Rate of compensation increase	3.62	%	3.62	%	3.50	%	3.50	%



Weighted-average assumptions used to determine net costs for years ended December 31	Pension Benefits				Other Benefits
	2017		2016		2017			2016
Discount rate	4.31	%	4.54	%	4.20	%		4.47	%
Expected long-term return on plan assets	6.73	%	7.14	%	2.00	%	*	2.54	%	*
Rate of compensation increase	3.62	%	3.62	%	3.50	%		3.50	%

Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]



	Increase		Decrease
	(millions)
Effect on total service and interest component	$	0.2	$	(0.2	)
Effect on post-retirement benefit obligation	0.4		(0.3		)

Pension Plans, Defined Benefit [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule of Allocation of Plan Assets [Table Text Block]



				Fair Value Measurements Using
Description	December 31 2017			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)			Assets measured at NAV
		(millions)
Pension Plans
Equity securities
U.S. ^(a)		$	279.8		$	236.4		$	—		$	—	$	43.4
International ^(b)		176.0			123.5			—			—		52.5
Real estate ^(c)		46.4			13.6			—			—		32.8
Commodities ^(d)		17.0			—			—			—		17.0
Fixed income securities
Fixed income funds ^(e)		71.8			21.4			—			—		50.4
U.S. Treasury		51.5			51.5			—			—		—
U.S. Agency, state and local obligations		18.3			—			18.3			—		—
U.S. corporate bonds ^(f)		119.2			—			119.2			—		—
Foreign corporate bonds		12.5			—			12.5			—		—
Hedge funds ^(g)		15.7			—			—			—		15.7
Cash equivalents		35.6			35.6			—			—		—
Other		4.6			—			4.6			—		—
Total		$	848.4		$	482.0		$	154.6		$	—	$	211.8



					Fair Value Measurements Using
Description	December 31 2016				Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)				Significant Unobservable Inputs (Level 3)			Assets measured at NAV
Pension Plans		(millions)
Equity securities
U.S. ^(a)		$	247.6			$	213.0		$	—			$	—	$	34.6
International ^(b)		163.7				120.4			—				—		43.3
Real estate ^(c)		42.7				12.4			—				—		30.3
Commodities ^(d)		14.1				—			—				—		14.1
Fixed income securities
Fixed income funds ^(e)		65.1				20.9			—				—		44.2
U.S. Treasury		52.2				52.2			—				—		—
U.S. Agency, state and local obligations		17.9				—			17.9				—		—
U.S. corporate bonds ^(f)		120.2				—			120.2				—		—
Foreign corporate bonds		9.3				—			9.3				—		—
Hedge funds ^(g)		15.6				—			—				—		15.6
Cash equivalents		31.7				31.7			—				—		—
Other		(3.3		)		—			(3.3		)		—		—
Total		$	776.8			$	450.6		$	144.1			$	—	$	182.1

^(d)Consists of institutional common/collective trust funds valued at NAV per share (or its equivalent) and is not categorized in the fair value hierarchy.

^(g)Consists of closely-held limited partnerships valued at NAV per share (or its equivalent) and is not categorized in the fair value hierarchy.

Other Postretirement Benefit Plans, Defined Benefit [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule of Allocation of Plan Assets [Table Text Block]



				Fair Value Measurements Using
Description	December 31 2017			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)			Assets measured at NAV
Other Post-Retirement Benefit Plans		(millions)
Equity securities		$	3.7		$	3.7		$	—		$	—	$	—
Fixed income securities
Fixed income fund^(a)		56.4			—			—			—		56.4
U.S. Treasury		3.0			3.0			—			—		—
U.S. Agency, state and local obligations		5.5			—			5.5			—		—
U.S. corporate bonds^(b)		18.7			—			18.7			—		—
Foreign corporate bonds		1.6			—			1.6			—		—
Cash equivalents		25.3			25.3			—			—		—
Mutual funds		0.2			0.2			—			—		—
Other		1.4			—			1.4			—		—
Total		$	115.8		$	32.2		$	27.2		$	—	$	56.4



				Fair Value Measurements Using
Description	December 31 2016			Quoted Prices in Active Markets for Identical Assets (Level 1)			Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)			Assets measured at NAV
Other Post-Retirement Benefit Plans		(millions)
Equity securities		$	4.1		$	4.1		$	—		$	—	$	—
Fixed income securities
Fixed income fund^(a)		62.7			—			—			—		62.7
U.S. Treasury		3.9			3.9			—			—		—
U.S. Agency, state and local obligations		4.3			—			4.3			—		—
U.S. corporate bonds^(b)		17.8			—			17.8			—		—
Foreign corporate bonds		1.6			—			1.6			—		—
Cash equivalents		19.5			19.5			—			—		—
Other		1.7			0.2			1.5			—		—
Total		$	115.6		$	27.7		$	25.2		$	—	$	62.7

Equity Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]

Equity compensation expense and associated income tax benefits



	2017		2016		2015
Great Plains Energy	(millions)
Equity compensation expense	$	6.3	$	5.0	$	4.0
Income tax benefit	2.4		1.6		1.4
KCP&L
Equity compensation expense	$	4.2	$	3.2	$	2.6
Income tax benefit	1.6		1.0		0.9

Performance share activity



	Performance Shares			Grant Date Fair Value*
Beginning balance January 1, 2017		625,100			$	28.13
Granted		236,433			31.26
Earned		(212,992	)		28.48
Forfeited		(103,454	)		29.24
Ending balance December 31, 2017		545,087			29.12

Restricted stock activity



	Nonvested Restricted Stock			Grant Date Fair Value*
Beginning balance January 1, 2017		249,672			$	27.20
Granted and issued		81,040			28.68
Vested		(112,813	)		26.92
Forfeited		(25,497	)		28.10
Ending balance December 31, 2017		192,402			27.87

Director Deferred Share Units



	Share Units			Grant Date Fair Value*
Beginning balance January 1, 2017		138,587			$	23.96
Issued		23,435			30.09
Converted		(22,871	)		21.81
Ending balance December 31, 2017		139,151			25.35

* weighted-average

- Definition

Tabular disclosure of an equity-based arrangement (such as stock or unit options and stock or unit awards) with an individual employee, which is generally an employment contract between the entity and a selected officer or key employee containing a promise by the employer to pay certain equity-based awards at future dates, sometimes including a period after retirement, upon compliance with stipulated requirements. This type of arrangement is distinguished from broader based employee benefit plans as it is usually tailored to the employee. Disclosure also typically includes the amount of related compensation expense recognized during the reporting period, the number of shares or units issued during the period under such arrangements, and the carrying amount as of the balance sheet date of the related liability.

+ References + Details

Long-Term Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Debt [Table Text Block]

Great Plains Energy's and KCP&L's long-term debt is detailed in the following table.



		December 31
	Year Due	2017				2016
KCP&L			(millions)
General Mortgage Bonds
2.95% EIRR bonds	2023		$	79.5			$	110.5
7.15% Series 2009A (8.59% rate)^(a)	2019		400.0				400.0
Senior Notes
5.85% Series (5.72% rate)^(a)			—				250.0
6.375% Series (7.49% rate)^(a)	2018		350.0				350.0
3.15% Series	2023		300.0				300.0
3.65% Series	2025		350.0				350.0
6.05% Series (5.78% rate)^(a)	2035		250.0				250.0
5.30% Series	2041		400.0				400.0
4.20% Series	2047		300.0				—
EIRR Bonds
1.329% Series 2007A and 2007B^(b)	2035		146.5				146.5
2.875% Series 2008	2038		23.4				23.4
Current maturities			(350.0		)		(281.0		)
Unamortized discount and debt issuance costs			(17.2		)		(15.4		)
Total KCP&L excluding current maturities^(c)			2,232.2				2,284.0
Other Great Plains Energy
GMO First Mortgage Bonds 9.44% Series	2018-2021		4.6				5.7
GMO Senior Notes
8.27% Series	2021		80.9				80.9
3.49% Series A	2025		125.0				125.0
4.06% Series B	2033		75.0				75.0
4.74% Series C	2043		150.0				150.0
GMO Medium Term Notes
7.33% Series	2023		3.0				3.0
7.17% Series	2023		7.0				7.0
Great Plains Energy Senior Notes
6.875% Series (7.33% rate)^(a)			—				100.0
4.85% Series	2021		350.0				350.0
5.292% Series	2022		287.5				287.5
Current maturities			(1.1		)		(101.1		)
Unamortized discount and premium, net and debt issuance costs			(1.5		)		(1.8		)
Total Great Plains Energy excluding current maturities^(c)			$	3,312.6			$	3,365.2


^(a)	Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments


^(b)	Variable rate


^(c)	At December 31, 2017 and 2016, does not include $50.0 million and $21.9 million of secured Series 2005 Environmental Improvement Revenue Refunding (EIRR) bonds because the bonds were repurchased in September 2015 and are held by KCP&L

Amortization Of Debt Expense [Table Text Block]

Great Plains Energy's and KCP&L's amortization of debt expense is detailed in the following table.



	2017		2016		2015
	(millions)
KCP&L	$	3.0	$	3.2	$	3.0
Other Great Plains Energy	26.9		30.6		1.1
Total Great Plains Energy	$	29.9	$	33.8	$	4.1

Schedule of Maturities of Long-term Debt [Table Text Block]

Great Plains Energy's and KCP&L's long-term debt maturities for the next five years are detailed in the following table.



	2018		2019		2020		2021		2022
	(millions)
Great Plains Energy	$	351.1	$	401.1	$	1.1	$	432.0	$	287.5
KCP&L	350.0		400.0		—		—		—

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Schedule of Rent Expense [Table Text Block]

Great Plains Energy's and KCP&L's expenses related to lease commitments are detailed in the following table.



	2017		2016		2015
	(millions)
Great Plains Energy	$	14.2	$	15.0	$	16.8
KCP&L	13.1		13.7		15.0

Unrecorded Unconditional Purchase Obligations And Lease Commitments [Table Text Block]



Great Plains Energy
	2018		2019		2020		2021		2022		After 2022			Total
Lease commitments	(millions)
Operating lease	$	12.1	$	9.3	$	9.7	$	9.7	$	9.5		$	101.0		$	151.3
Capital lease	0.4		0.4		0.4		0.4		0.4			2.7			4.7
Purchase commitments
Fuel	210.4		180.1		67.3		5.1		37.4			80.7			581.0
Power	47.3		47.3		47.3		47.4		47.6			414.6			651.5
Other	20.9		14.7		6.7		5.5		2.4			35.9			86.1
Total contractual commitments	$	291.1	$	251.8	$	131.4	$	68.1	$	97.3		$	634.9		$	1,474.6



KCP&L
	2018		2019		2020		2021		2022		After 2022			Total
Lease commitments	(millions)
Operating lease	$	11.3	$	9.3	$	9.7	$	9.7	$	9.5		$	101.0		$	150.5
Capital lease	0.2		0.2		0.2		0.2		0.2			1.4			2.4
Purchase commitments
Fuel	177.5		159.8		51.8		5.1		37.4			80.7			512.3
Power	34.8		34.8		34.8		34.9		35.1			289.8			464.2
Other	20.0		12.7		5.8		4.6		1.6			31.4			76.1
Total contractual commitments	$	243.8	$	216.8	$	102.3	$	54.5	$	83.8		$	504.3		$	1,205.5

Schedule Of Environmental Capital Expenditures [Table Text Block]



	2018		2019		2020		2021		2022
	(millions)
Great Plains Energy	$	14.6	$	2.8	$	7.7	$	20.1	$	63.1
KCP&L	14.5		2.8		7.7		20.1		63.1

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair value of assets and liabilities

The following tables include Great Plains Energy's and KCP&L's balances of financial assets and liabilities measured at fair value on a recurring basis.



Description	December 31 2017			Level 1		Level 2			Level 3
KCP&L		(millions)
Assets
Nuclear decommissioning trust ^(a)
Equity securities		$	183.8	$	183.8		$	—		$	—
Debt securities
U.S. Treasury		35.3		35.3			—			—
U.S. Agency		0.4		—			0.4			—
State and local obligations		2.1		—			2.1			—
Corporate bonds		34.1		—			34.1			—
Foreign governments		0.1		—			0.1			—
Cash equivalents		2.5		2.5			—			—
Other		0.1		0.1			—			—
Total nuclear decommissioning trust		258.4		221.7			36.7			—
Self-insured health plan trust ^(b)
Equity securities		0.5		0.5			—			—
Debt securities		2.7		0.3			2.4			—
Cash and cash equivalents		7.7		7.7			—			—
Total self-insured health plan trust		10.9		8.5			2.4			—
Total		$	269.3	$	230.2		$	39.1		$	—
Other Great Plains Energy
Assets
Interest rate derivative instruments ^(c)		$	91.4	$	—		$	—		$	91.4
Total		$	91.4	$	—		$	—		$	91.4
Great Plains Energy
Assets
Nuclear decommissioning trust ^(a)		$	258.4	$	221.7		$	36.7		$	—
Self-insured health plan trust ^(b)		10.9		8.5			2.4			—
Interest rate derivative instruments ^(c)		91.4		—			—			91.4
Total		$	360.7	$	230.2		$	39.1		$	91.4



Description	December 31 2016			Level 1			Level 2			Level 3
KCP&L		(millions)
Assets
Nuclear decommissioning trust ^(a)
Equity securities		$	153.9		$	153.9		$	—		$	—
Debt securities
U.S. Treasury		27.8			27.8			—			—
U.S. Agency		1.7			—			1.7			—
State and local obligations		3.2			—			3.2			—
Corporate bonds		32.4			—			32.4			—
Foreign governments		0.1			—			0.1			—
Cash equivalents		3.8			3.8			—			—
Total nuclear decommissioning trust		222.9			185.5			37.4			—
Self-insured health plan trust ^(b)
Equity securities		0.9			0.9			—			—
Debt securities		4.8			0.1			4.7			—
Cash and cash equivalents		5.6			5.6			—			—
Total self-insured health plan trust		11.3			6.6			4.7			—
Total		$	234.2		$	192.1		$	42.1		$	—
Other Great Plains Energy
Assets
Interest rate derivative instruments ^(c)		$	79.3		$	—		$	—		$	79.3
Total		$	79.3		$	—		$	—		$	79.3
Great Plains Energy
Assets
Nuclear decommissioning trust ^(a)		$	222.9		$	185.5		$	37.4		$	—
Self-insured health plan trust ^(b)		11.3			6.6			4.7			—
Interest rate derivative instruments ^(c)		79.3			—			—			79.3
Total		$	313.5		$	192.1		$	42.1		$	79.3


^(a)	Fair value is based on quoted market prices of the investments held by the fund and/or valuation models.


^(b)	Fair value is based on quoted market prices of the investments held by the trust. Debt securities classified as Level 1 are comprised of U.S. Treasury securities. Debt securities classified as Level 2 are comprised of corporate bonds, U.S. Agency, state and local obligations, and other asset-backed securities.

^(c)

Unobservable inputs reconciliation

The following table reconciles the beginning and ending balances for all Level 3 assets measured at fair value on a recurring basis.



Great Plains Energy
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
	Derivative Instruments
	2017			2016
	(millions)
Net asset at January 1	$	79.3		$	—
Total realized/unrealized gains (losses):
included in interest charges	(1.9		)	79.3
included in non-operating income	14.0			—
included in loss on Series B Preferred Stock dividend make-whole provisions	(124.8		)	—
Settlements	124.8			—
Net asset at December 31	$	91.4		$	79.3
Total unrealized gains (losses) relating to assets still on the consolidated balance sheet at December 31:
included in interest charges	$	(1.9	)	$	79.3
included in non-operating income	$	14.0		$	—

See Note 14 for additional information concerning the Series B Preferred Stock dividend make-whole provisions.

Accumulated Other Comprehensive Income (Loss) (Tables)

12 Months Ended

Dec. 31, 2017

Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

The following tables reflect the change in the balances of each component of accumulated other comprehensive income (loss) for Great Plains Energy and KCP&L.



Great Plains Energy
	Gains and Losses on Cash Flow Hedges^(a)				Defined Benefit Pension Items^(a)				Total^(a)
	(millions)
2017
Beginning balance January 1		$	(4.5	)		$	(2.1	)	$	(6.6	)
Other comprehensive loss before reclassification		—				(0.9		)	(0.9		)
Amounts reclassified from accumulated other comprehensive loss		4.9				0.4			5.3
Net current period other comprehensive income (loss)		4.9				(0.5		)	4.4
Ending balance December 31		$	0.4			$	(2.6	)	$	(2.2	)
2016
Beginning balance January 1		$	(10.1	)		$	(1.9	)	$	(12.0	)
Other comprehensive loss before reclassifications		—				(0.7		)	(0.7		)
Amounts reclassified from accumulated other comprehensive loss		5.6				0.5			6.1
Net current period other comprehensive income (loss)		5.6				(0.2		)	5.4
Ending balance December 31		$	(4.5	)		$	(2.1	)	$	(6.6	)

^(a) Net of tax



KCP&L
	Gains and Losses on Cash Flow Hedges^(a)
	(millions)
2017
Beginning balance January 1		$	(4.2	)
Amounts reclassified from accumulated other comprehensive loss		4.6
Net current period other comprehensive income		4.6
Ending balance December 31		$	0.4
2016
Beginning balance January 1		$	(9.6	)
Amounts reclassified from accumulated other comprehensive loss		5.4
Net current period other comprehensive income		5.4
Ending balance December 31		$	(4.2	)

^(a) Net of tax

Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]



Great Plains Energy
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Loss						Affected Line Item in the Income Statement
	2017			2016
	(millions)
Gains (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(7.9	)	$	(9.2	)	Interest charges
	(7.9		)	(9.2		)	Income before income tax expense and income from equity investments
	3.0			3.6			Income tax benefit
	$	(4.9	)	$	(5.6	)	Net income (loss)
Amortization of defined benefit pension items
Net losses included in net periodic benefit costs	$	(0.7	)	$	(0.8	)	Utility operating and maintenance expenses
	(0.7		)	(0.8		)	Income before income tax expense and income from equity investments
	0.3			0.3			Income tax benefit
	$	(0.4	)	$	(0.5	)	Net income (loss)

Total reclassifications, net of tax	$	(5.3	)	$	(6.1	)	Net income (loss)



KCP&L
Details about Accumulated Other Comprehensive Loss Components	Amount Reclassified from Accumulated Other Comprehensive Income (Loss)						Affected Line Item in the Income Statement
	2017			2016
	(millions)
Gains (losses) on cash flow hedges (effective portion)
Interest rate contracts	$	(7.5	)	$	(8.8	)	Interest charges
	(7.5		)	(8.8		)	Income before income tax expense
	2.9			3.4			Income tax benefit
Total reclassifications, net of tax	$	(4.6	)	$	(5.4	)	Net income

Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

21. TAXES

Components of income tax expense are detailed in the following tables.



Great Plains Energy	2017			2016			2015
Current income taxes	(millions)
Federal	$	(1.7	)	$	0.3		$	(0.2	)
State	1.0			0.7			(1.1		)
Total	(0.7		)	1.0			(1.3		)
Deferred income taxes
Federal	223.5			140.6			96.9
State	11.9			29.5			28.0
Total	235.4			170.1			124.9
Investment tax credit
Deferral	—			2.5			0.5
Amortization	(1.4		)	(1.4		)	(1.4		)
Total	(1.4		)	1.1			(0.9		)
Income tax expense	$	233.3		$	172.2		$	122.7

Great Plains Energy's 2017 federal deferred income tax expense includes $130.3 million of additional income tax expense due to the impacts of U.S. federal income tax reform, discussed further below.



KCP&L	2017			2016			2015
Current income taxes	(millions)
Federal	$	37.4		$	24.8		$	(18.7	)
State	8.3			4.7			(3.4		)
Total	45.7			29.5			(22.1		)
Deferred income taxes
Federal	74.7			76.4			81.9
State	8.8			17.0			17.5
Total	83.5			93.4			99.4
Investment tax credit
Deferral	—			—			0.5
Amortization	(1.0		)	(1.0		)	(1.0		)
Total	(1.0		)	(1.0		)	(0.5		)
Income tax expense	$	128.2		$	121.9		$	76.8

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

Effective income tax rates reflected in the financial statements and the reasons for their differences from the statutory federal rates are detailed in the following tables.



Great Plains Energy	2017		2016		2015
Federal statutory income tax rate	35.0	%	35.0	%	35.0	%
Differences between book and tax depreciation not normalized	0.1		(0.1	)	—
Amortization of investment tax credits	(1.1	)	(0.3	)	(0.4	)
Federal income tax credits	(5.8	)	(2.6	)	(4.1	)
State income taxes	8.3		4.2		4.0
Transaction-related costs	42.5		0.9		—
Valuation allowance	8.9		—		1.5
Federal tax rate change	95.3		—		—
Other	0.3		0.2		0.5
Effective income tax rate	183.5	%	37.3	%	36.5	%



KCP&L	2017		2016		2015
Federal statutory income tax rate	35.0	%	35.0	%	35.0	%
Differences between book and tax depreciation not normalized	(0.1	)	(0.3	)	—
Amortization of investment tax credits	(0.3	)	(0.3	)	(0.5	)
Federal income tax credits	(2.4	)	(3.1	)	(5.6	)
State income taxes	3.8		4.1		4.0
Valuation allowance	0.4		—		0.3
Federal tax rate change	5.3		—		—
Other	(0.1	)	(0.2	)	0.3
Effective income tax rate	41.6	%	35.2	%	33.5	%

Summary of Operating Loss Carryforwards [Table Text Block]

The year of origin of Great Plains Energy's related tax benefit amounts for federal NOL carryforwards as of December 31, 2017 are detailed in the following table.



	Amount of
Year of Origin	Benefit
	(millions)
2003	$	9.5
2004	91.4
2005	44.4
2006	32.0
2007	0.8
2008	1.4
2009	21.9
2010	2.5
2011	65.3
2012	0.2
2013	0.8
2014	52.0
2015	59.2
2016	0.6
	$	382.0

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

The tax effects of major temporary differences resulting in deferred income tax assets (liabilities) in the consolidated balance sheets are in the following tables.



	Great Plains Energy						KCP&L
December 31	2017			2016			2017			2016
Noncurrent deferred income taxes	(millions)
Plant related	$	(1,549.0	)	$	(2,107.6	)	$	(1,114.9	)	$	(1,492.2	)
Income taxes on future regulatory refunds (recoveries)	236.0			(148.7		)	179.1			(123.9		)
Derivative instruments	(19.2		)	(17.0		)	1.6			8.5
Pension and post-retirement benefits	9.4			10.5			28.6			38.6
SO₂emission allowance sales	14.9			24.1			15.0			24.1
Fuel recovery mechanisms	(17.9		)	(22.3		)	(15.9		)	(27.2		)
Tax credit carryforwards	279.8			271.1			185.8			177.4
Customer demand programs	(17.4		)	(34.3		)	(11.7		)	(21.8		)
Solar rebates	(15.2		)	(27.3		)	(5.8		)	(11.4		)
Net operating loss carryforward	473.0			718.0			131.2			198.3
Other	6.9			20.2			(9.1		)	1.3
Net noncurrent deferred income tax liability before valuation allowance	(598.7		)	(1,313.3		)	(616.1		)	(1,228.3		)
Valuation allowance	(23.0		)	(16.4		)	—			—
Net noncurrent deferred income tax liability	$	(621.7	)	$	(1,329.7	)	$	(616.1	)	$	(1,228.3	)



	Great Plains Energy						KCP&L
December 31	2017			2016			2017			2016
	(millions)
Gross deferred income tax assets	$	2,017.4		$	1,360.9		$	1,261.5		$	747.7
Gross deferred income tax liabilities	(2,639.1		)	(2,690.6		)	(1,877.6		)	(1,976.0		)
Net deferred income tax liability	$	(621.7	)	$	(1,329.7	)	$	(616.1	)	$	(1,228.3	)

Segments and Related Information (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Segment Financial Information [Table Text Block]

The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment.



2017	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,708.2			$	—			$	—		$	2,708.2
Depreciation and amortization		(371.1		)		—				—			(371.1		)
Interest charges		(196.9		)		(125.9		)		32.1			(290.7		)
Income tax expense		(169.4		)		(63.9		)		—			(233.3		)
Net income (loss)		256.9				(363.1		)		—			(106.2		)



2016	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,676.0			$	—			$	—		$	2,676.0
Depreciation and amortization		(344.8		)		—				—			(344.8		)
Interest charges		(196.1		)		2.5				32.1			(161.5		)
Income tax expense		(164.3		)		(7.9		)		—			(172.2		)
Net income (loss)		292.1				(2.1		)		—			290.0



2015	Electric Utility				Other				Eliminations			Great Plains Energy
		(millions)
Operating revenues		$	2,502.2			$	—			$	—		$	2,502.2
Depreciation and amortization		(330.4		)		—				—			(330.4		)
Interest charges		(190.9		)		(40.5		)		32.1			(199.3		)
Income tax expense		(120.8		)		(1.9		)		—			(122.7		)
Net income (loss)		223.8				(10.8		)		—			213.0



	Electric Utility			Other				Eliminations				Great Plains Energy
2017		(millions)
Assets		$	11,508.1		$	1,285.7			$	(335.9	)		$	12,457.9
Capital expenditures		573.5			—				—				573.5
2016
Assets		$	11,444.2		$	2,461.3			$	(335.5	)		$	13,570.0
Capital expenditures		609.4			—				—				609.4
2015
Assets		$	11,045.5		$	(51.1	)		$	(255.8	)		$	10,738.6
Capital expenditures		677.1			—				—				677.1

Jointly Owned Electric Utility Plants (Tables)

12 Months Ended

Dec. 31, 2017

Jointly Owned Electric Utility Plants [Abstract]

Schedule of Jointly Owned Utility Plants [Table Text Block]



Great Plains Energy
	Wolf Creek Unit			La Cygne Units			Iatan No. 1 Unit			Iatan No. 2 Unit			Iatan Common			Jeffrey Energy Center
	(millions, except MW amounts)
Great Plains Energy's share		47%			50%			88%			73%			79%			8%

Utility plant in service		$	1,854.2		$	1,191.1		$	699.9		$	1,355.8		$	491.1		$	201.1
Accumulated depreciation		918.1			347.8			280.8			413.0			130.7			82.0
Nuclear fuel, net		72.4			—			—			—			—			—
Construction work in progress		91.8			8.6			31.8			35.0			21.7			2.5
2018 accredited capacity-MWs		552			699			616			641			NA			173



KCP&L
	Wolf Creek Unit			La Cygne Units			Iatan No. 1 Unit			Iatan No. 2 Unit			Iatan Common
	(millions, except MW amounts)
KCP&L's share		47%			50%			70%			55%			61%

Utility plant in service		$	1,854.2		$	1,191.1		$	561.7		$	1,041.6		$	401.8
Accumulated depreciation		918.1			347.8			228.9			366.6			117.5
Nuclear fuel, net		72.4			—			—			—			—
Construction work in progress		91.8			8.6			7.6			14.8			12.0
2018 accredited capacity-MWs		552			699			490			482			NA

Quarterly Operating Results (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]



	Quarter
Great Plains Energy	1st			2nd			3rd		4th
2017	(millions, except per share amounts)
Operating revenue	$	570.7		$	682.6		$	857.2	$	597.7
Operating income	47.4			176.5			305.9		73.8
Net income (loss)	(9.6		)	(7.0		)	10.5		(100.1		)
Basic and diluted earnings (loss) per common share	(0.11		)	(0.10		)	0.02		(0.46		)
2016
Operating revenue	$	572.1		$	670.8		$	856.8	$	576.3
Operating income	89.9			182.3			281.9		64.8
Net income	26.4			32.0			133.6		98.0
Basic and diluted earnings per common share	0.17			0.20			0.86		0.39



	Quarter
KCP&L	1st		2nd		3rd		4th
2017	(millions)
Operating revenue	$	395.9	$	482.7	$	595.7	$	416.4
Operating income	58.2		113.8		209.9		61.8
Net income	14.2		49.6		114.1		1.9
2016
Operating revenue	$	400.9	$	475.6	$	597.6	$	401.3
Operating income	70.6		137.9		219.2		54.4
Net income	24.6		65.9		117.7		16.8

Summary of Significant Accounting Policies Equity Method Investment (Details) - Transource Energy, LLC [Member]	12 Months Ended
	Dec. 31, 2017 Rate
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Description of Principal Activities	Transource is focused on the development of competitive electric transmission projects.
GPE Transmission Holding Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	13.50%
AEP Transmission Holding Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage of Majority Owner	86.50%

Summary of Significant Accounting Policies Summary of Significant Accounting Policies Utility Plant (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	3.00%
Depreciation	$ 330.8	$ 308.8	$ 299.4
Depreciation and amortization	371.1	344.8	$ 330.4
Plant to be retired, net	143.6	0.0
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Generation or Processing	7,930.8	8,106.4
Public Utilities, Property, Plant and Equipment, Transmission	912.3	886.3
Public Utilities, Property, Plant and Equipment, Distribution	3,789.0	3,629.1
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	1,042.0	975.9
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 13,674.1	13,597.7
Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	20 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	15 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	8 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	5 years
Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	60 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	70 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	66 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	50 years
Land and other assets not depreciated [Member]
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 265.0	$ 261.2
KCPL Greater Missouri Operations [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	1.90%	1.60%	4.20%
KCPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation	$ 228.4	$ 215.4	$ 208.5
Depreciation and amortization	$ 266.3	$ 247.5	$ 235.7
Public Utilities, Allowance for Funds Used During Construction, Rate	4.90%	5.70%	3.00%
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Generation or Processing	$ 6,471.5	$ 6,350.7
Public Utilities, Property, Plant and Equipment, Transmission	500.4	484.1
Public Utilities, Property, Plant and Equipment, Distribution	2,389.4	2,298.4
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	851.9	791.9
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 10,213.2	9,925.1
KCPL [Member] \| Minimum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	20 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	15 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	8 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	5 years
KCPL [Member] \| Maximum [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Property, Plant and Equipment, Generation, Useful Life	60 years
Public Utilities, Property, Plant and Equipment, Transmission, Useful Life	70 years
Public Utilities, Property, Plant and Equipment, Distribution, Useful Life	55 years
Public Utilities, Property, Plant and Equipment, Other Property Plant and Equipment, Useful Life	50 years
KCPL [Member] \| Land and other assets not depreciated [Member]
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 176.0	$ 178.0

Summary of Significant Accounting Policies Summary of Significant Accounting Policies Revenue Recognition and Non-Operating Income and Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Nonoperating Expense	$ 31.4	$ 14.3	$ 8.0
Other Nonoperating Income, Interest Income on Proceeds	22.8
Other Nonoperating Income, Mark To Market Gains	14.0
Other Nonoperating Expense, Write-off Deferred Offering Fees	15.0
KCPL [Member]
Other Nonoperating Expense	8.1	7.6	7.2
KCPL [Member] \| MISSOURI
Excise and Sales Taxes	$ 72.9	$ 70.3	$ 62.0

Summary of Significant Accounting Policies Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income [Abstract]
Net income (loss)									$ (106.2)	$ 290.0	$ 213.0
Less: preferred stock dividend requirements and redemption premium									37.3	16.5	1.6
Earnings (loss) available for common shareholders									$ (143.5)	$ 273.5	$ 211.4
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)									215.5	169.4	154.2
Add: effect of dilutive securities (in shares)									0.0	0.4	0.6
Diluted average number of common shares outstanding (in shares)									215.5	169.8	154.8
Earnings Per Share [Abstract]
Basic and Diluted EPS	$ (0.46)	$ 0.02	$ (0.10)	$ (0.11)	$ 0.39	$ 0.86	$ 0.20	$ 0.17	$ (0.67)	$ 1.61	$ 1.37
Series B Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage									7.00%	7.00%

Summary of Significant Accounting Policies Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assumed conversion of Series B Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		7,805,460
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	226,958
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	144,989		900

Summary of Significant Accounting Policies Subsequent Events (Details) - Subsequent Event [Member]	Feb. 28, 2018 $ / shares
Common Stock [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 0.275
Dividends Payable, Date of Record	Feb. 27, 2018
Dividends Payable, Date Declared, Month and Year	2018-02
Dividends Payable, Date to be Paid	Mar. 20, 2018
KCPL [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 60,000,000
Dividends Payable, Date Declared, Month and Year	2018-02
Dividends Payable, Date to be Paid	Mar. 19, 2018

Anticipated Merger with Westar Energy, Inc. (Details) $ / shares in Units, $ in Millions			1 Months Ended			12 Months Ended
	Jul. 09, 2017 Rate	May 29, 2016 USD ($) $ / shares shares	Jul. 31, 2017 USD ($) Rate	Mar. 31, 2017 USD ($)	Oct. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) Rate shares	Dec. 31, 2016 USD ($) Rate shares	Dec. 31, 2015 USD ($) shares
Anticipated Merger With Westar Energy, Inc. [Line Items]
Cash consideration to be transferred (per share) \| $ / shares		$ 51.00
Issuance of long-term debt						$ 4,591.1	$ 0.0	$ 348.8
Minimum Required Cash Balance at Closing of Anticipated Merger with Westar						1,250.0
GPE 4.3 Billion Senior Notes [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Long-term Debt, Gross						4,300.0
Debt Instrument, Redemption Price, Percentage \| Rate			101.00%
Westar Energy Inc [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Holdco Common Stock Conversion Ratio \| Rate	1.0
Ownership in Holdco - Percentage \| Rate	52.50%
Merger Termination Fee Westar Termination						$ 190.0
Great Plains Energy [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Preferred Stock, Dividend Rate, Percentage \| Rate						7.00%	7.00%
Issuance of long-term debt						$ 4,291.9	$ 0.0	$ 0.0
Holdco Common Stock Conversion Ratio \| Rate	0.5981
Merger Termination Fee Regulatory Approvals						190.0
Merger Termination Fee Great Plains Energy						190.0
Ownership in Holdco - Percentage \| Rate	47.50%
Merger Termination Fee Original Merger Agreement						380.0
Great Plains Energy [Member] \| GPE 4.3 Billion Senior Notes [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Issuance of long-term debt				$ 4,300.0
Long-term Debt, Gross			$ 4,300.0	$ 4,300.0
Bridge Loan [Member] \| Great Plains Energy [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Amount of bridge facility						8,017.0
Amount of bridge facility, as amended			864.5			$ 864.5
Series A Preferred Stock [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Preferred Shares To Be Issued, Stock Purchase Agreement, Series A Preferred Stock \| shares		750,000				750,000
Preferred Stock, Dividend Rate, Percentage \| Rate						7.25%
Preferred Stock, Purchase Agreement, Proceeds		$ 750.0	750.0			$ 750.0
Previously deferred offering costs written off			$ 15.0
Depositary Shares [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues \| shares					17,300,000
Shares Issued, Price Per Share \| $ / shares					$ 50
Net Proceeds from Issuance of Depositary Shares					$ 836.2
Gross Proceeds from Issuance of Depositary Shares					$ 862.5
Series B Preferred Stock [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Preferred Stock, Dividend Rate, Percentage \| Rate						7.00%	7.00%
Common Stock [Member]
Anticipated Merger With Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues \| shares					60,500,000	322,618	60,974,205	250,863
Shares Issued, Price Per Share \| $ / shares					$ 26.45
Net Proceeds from Issuance of Common Stock					$ 1,550.0

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows affected by changes in:
Receivables	$ 14.8	$ (18.3)	$ 12.5
Accounts receivable pledged as collateral	(7.6)	2.6	(4.0)
Fuel inventories	5.6	9.6	(28.3)
Materials and supplies	(9.0)	(6.5)	(3.0)
Accounts payable	9.0	(25.4)	(11.4)
Accrued taxes	1.5	8.1	1.1
Accrued interest	(8.0)	6.1	3.4
Deferred refueling outage costs	15.5	(3.1)	(6.7)
Pension and post-retirement benefit obligations	26.1	27.4	18.5
Allowance for equity funds used during construction	(6.0)	(6.6)	(4.8)
Fuel recovery mechanisms	(11.4)	(46.9)	47.5
ARO settlements	(28.5)	(17.4)	(4.1)
Other	20.6	28.1	(7.8)
Total other operating activities	22.6	(42.3)	12.9
Cash paid during the period:
Interest	258.9	191.2	182.2
Income taxes	0.0	0.1	0.1
Non-cash investing activities:
Liabilities accrued for capital expenditures	39.8	32.4	35.7
KCPL [Member]
Cash flows affected by changes in:
Receivables	13.8	(12.4)	2.6
Accounts receivable pledged as collateral	(20.0)	0.0	0.0
Fuel inventories	1.9	10.6	(24.7)
Materials and supplies	(7.1)	(4.3)	(4.5)
Accounts payable	11.7	(30.5)	(18.0)
Accrued taxes	9.1	67.9	(19.0)
Accrued interest	0.0	0.0	3.4
Deferred refueling outage costs	15.5	(3.1)	(6.7)
Pension and post-retirement benefit obligations	27.3	28.6	18.4
Allowance for equity funds used during construction	(6.0)	(6.6)	(3.8)
Fuel recovery mechanisms	8.3	(53.7)	3.5
ARO settlements	(25.5)	(15.0)	(4.1)
Other	(9.0)	16.4	(8.6)
Total other operating activities	20.0	(2.1)	(61.5)
Cash paid during the period:
Interest	128.0	127.0	120.2
Income taxes	38.8	0.0	0.0
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 32.9	$ 27.2	$ 23.9

Receivables Accounts, Notes, and Financing (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 49.5	$ 64.7
Total	151.7	166.0
KCPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	39.3	51.7
Total	106.3	139.1
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(4.7)	(4.0)
Trade Accounts Receivable [Member] \| KCPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(2.2)	(1.8)
Trade Accounts Receivable [Member] \| Billed Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	3.7	26.2
Trade Accounts Receivable [Member] \| Billed Revenues [Member] \| KCPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	1.6	25.5
Trade Accounts Receivable [Member] \| Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	103.2	79.1
Trade Accounts Receivable [Member] \| Unbilled Revenues [Member] \| KCPL [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	$ 67.6	$ 63.7

Receivables Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	$ 180.0	$ 172.4
Collateralized note payable	180.0	172.4
KCPL Greater Missouri Operations [Member]
Sale Of Accounts Receivable - KCPL and GMO
Maximum amount of outstanding principal under receivables agreement from mid-November to mid-June	50.0
Maximum amount of outstanding principal under receivables agreement from mid-June to mid-November	65.0
KCPL [Member]
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	130.0	110.0
Collateralized note payable	130.0	$ 110.0
Maximum amount of outstanding principal under receivables agreement	$ 130.0

Nuclear Plant (Details) - USD ($) $ in Millions	12 Months Ended
Nuclear Plant (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments in decommissioning trust fund [Line Items]
Cost Basis	$ 168.8	$ 160.5
Unrealized Gains	91.0	64.4
Unrealized Losses	(1.4)	(2.0)
Fair Value	$ 258.4	222.9	$ 200.7
Weighted average maturity of debt securities (in years)	9 years
Realized gains	$ 2.5	1.6	5.3
Realized losses	(1.8)	(1.3)	$ (4.6)
Equity Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	96.5	93.3
Unrealized Gains	88.3	62.1
Unrealized Losses	(1.0)	(1.5)
Fair Value	183.8	153.9
Debt Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	69.7	63.4
Unrealized Gains	2.7	2.3
Unrealized Losses	(0.4)	(0.5)
Fair Value	72.0	65.2
Other Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	2.6	3.8
Fair Value	$ 2.6	$ 3.8

Nuclear Plant Decommissioning Trust (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2017
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	$ 222.9	$ 200.7
Contributions	3.3	3.3
Earned income, net of fees	4.3	4.1
Net realized gains	0.7	0.3
Net unrealized gains	27.2	14.5
Ending balance December 31	$ 258.4	222.9
Nuclear Insurance [Abstract]
Industry aggregate limit on nuclear insurance for property claims including accidental damages			$ 3,200.0
Industry aggregate limit on non-nuclear acts of terrorism			1,800.0
Amount of insurance against public liability claims resulting from nuclear incidents to full limit of public liability			13,500.0
Maximum available commercial insurance			500.0
Remaining balance provided through industry wide retrospective assesment program mandated by law			13,000.0
Maximum amount able to be assessed to owners			127.3
SFP Program-annual amount payable per incident			19.0
Amount of decontamination liability, premature decommissioning liability and property damage insurance			2,800.0
Premature decommissioning coverage applies only if property damage exceeds this amount and trust funds have been exhausted			500.0
Estimated maximum amount of retrospective assessments under the current policies			37.4
Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)				47.00%
Wolf Creek [Member] \| Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current Cost of Decommissioning (in 2017 Dollars)			813.7
Future cost of decommissioning (in 2045 through 2053 dollars)			2,137.8
Annual Escalation Factor	3.16%
Annual return on trust assets through 2027	5.46%
Annual return on trusts assets in 2053	2.22%
Wolf Creek [Member] \| Kansas Corporation Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current Cost of Decommissioning (in 2017 Dollars)			813.7
Future cost of decommissioning (in 2045 through 2053 dollars)			1,982.4
Annual Escalation Factor	2.91%
Annual return on trust assets through 2029	5.64%
Annual return on trusts assets in 2053	0.32%
KCPL [Member]
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	$ 222.9	200.7
Contributions	3.3	3.3
Earned income, net of fees	4.3	4.1
Net realized gains	0.7	0.3
Net unrealized gains	27.2	14.5
Ending balance December 31	$ 258.4	$ 222.9
KCPL [Member] \| Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%			47.00%
KCPL [Member] \| Wolf Creek [Member] \| Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current Cost of Decommissioning (in 2017 Dollars)			382.5
Future cost of decommissioning (in 2045 through 2053 dollars)			1,004.8
KCPL [Member] \| Wolf Creek [Member] \| Kansas Corporation Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current Cost of Decommissioning (in 2017 Dollars)			382.5
Future cost of decommissioning (in 2045 through 2053 dollars)			931.7
KCPL [Member] \| Nuclear Plant [Member]
Nuclear Insurance [Abstract]
Maximum amount able to be assessed to owners			59.8
SFP Program-annual amount payable per incident			8.9
Amount of decontamination liability, premature decommissioning liability and property damage insurance			1,300.0
Estimated maximum amount of retrospective assessments under the current policies			$ 17.6

Regulatory Matters (Details) - KCPL [Member] - USD ($) $ in Millions	1 Months Ended
	May 31, 2017	Apr. 30, 2017	Nov. 30, 2016	Jul. 31, 2016
Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue increase, requested, portion related to rebasing fuel and purchased power expense				$ 27.2
Annual revenue increase (decrease), requested, not including rebasing fuel and purchased power expense				$ 62.9
Annual revenue increase, authorized, portion related to rebasing fuel and purchased power expense	$ 27.1
Annual revenue increase, authorized, not including rebasing fuel and purchased power expense	$ 5.4
Return on equity, requested (in hundredths)				9.90%
Rate-making equity ratio, requested (in hundredths)				49.88%
Return on equity, approved (in hundredths)	9.50%
Ratemaking equity ratio, approved (in hundredths)	49.20%
Kansas Corporation Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue decrease, requested			$ 2.8
Public Utilities, KCPL and Commission Staff Recommended Rate Decrease, Amount		$ 3.6

Regulatory Matters Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,106.3	$ 309.9
Taxes refundable through future rates [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	794.6	0.0
Emission allowances [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	58.1	62.1
Asset retirement obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	126.0	99.7
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	57.4	65.1
Deferred Fuel Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3.9	11.6
Pension [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	20.2	22.7
Other Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	46.1	48.7
KCPL Greater Missouri Operations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	327.1	122.5
KCPL Greater Missouri Operations [Member] \| Taxes refundable through future rates [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	220.6	0.0
KCPL Greater Missouri Operations [Member] \| Emission allowances [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
KCPL Greater Missouri Operations [Member] \| Asset retirement obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
KCPL Greater Missouri Operations [Member] \| Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	57.4	65.1
KCPL Greater Missouri Operations [Member] \| Deferred Fuel Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3.9	11.6
KCPL Greater Missouri Operations [Member] \| Pension [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	8.2	7.4
KCPL Greater Missouri Operations [Member] \| Other Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	37.0	38.4
KCPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	779.2	187.4
KCPL [Member] \| Taxes refundable through future rates [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	574.0	0.0
KCPL [Member] \| Emission allowances [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	58.1	62.1
KCPL [Member] \| Asset retirement obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	126.0	99.7
KCPL [Member] \| Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
KCPL [Member] \| Deferred Fuel Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0.0	0.0
KCPL [Member] \| Pension [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	12.0	15.3
KCPL [Member] \| Other Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 9.1	$ 10.3

Regulatory Matters Regulatory Matters Subsequent Events (Details) - MissouriPublicServiceCommission [Member] - USD ($) $ in Millions	1 Months Ended
	Jan. 31, 2018	Jul. 31, 2016
Kcpl Greater Missouri Operations Member \| Subsequent Event [Member]
Subsequent Event [Line Items]
Public Utilities, Requested Return on Equity, Percentage	9.85%
Annual revenue increase (decrease), requested, not including rebasing fuel and purchased power expense	$ (2.4)
Annual revenue increase, requested, portion related to rebasing fuel and purchased power expense	$ 21.7
Public Utilities, Requested Equity Capital Structure, Percentage	54.40%
KCPL [Member]
Subsequent Event [Line Items]
Public Utilities, Requested Return on Equity, Percentage		9.90%
Annual revenue increase (decrease), requested, not including rebasing fuel and purchased power expense		$ 62.9
Annual revenue increase, requested, portion related to rebasing fuel and purchased power expense		$ 27.2
Public Utilities, Requested Equity Capital Structure, Percentage		49.88%
KCPL [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Public Utilities, Requested Return on Equity, Percentage	9.85%
Annual revenue increase (decrease), requested, not including rebasing fuel and purchased power expense	$ 8.9
Annual revenue increase, requested, portion related to rebasing fuel and purchased power expense	$ 7.5
Public Utilities, Requested Equity Capital Structure, Percentage	50.03%

Intangibles Assets (Details) - USD ($) $ in Millions	12 Months Ended
Intangibles Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 33.7	$ 29.1
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	30.5
Finite-Lived Intangible Assets, Amortization Expense, Year Two	25.7
Finite-Lived Intangible Assets, Amortization Expense, Year Three	24.5
Finite-Lived Intangible Assets, Amortization Expense, Year Four	20.0
Finite-Lived Intangible Assets, Amortization Expense, Year Five	14.9
KCPL [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	32.1	25.7
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	29.7
Finite-Lived Intangible Assets, Amortization Expense, Year Two	25.0
Finite-Lived Intangible Assets, Amortization Expense, Year Three	23.8
Finite-Lived Intangible Assets, Amortization Expense, Year Four	19.5
Finite-Lived Intangible Assets, Amortization Expense, Year Five	14.5
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	386.8	355.2
Finite-Lived Intangible Assets, Accumulated Amortization	(251.2)	(219.1)
Computer Software, Intangible Asset [Member] \| KCPL [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	368.7	338.3
Finite-Lived Intangible Assets, Accumulated Amortization	(234.3)	(203.1)
Asset Improvements [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	30.3	28.8
Finite-Lived Intangible Assets, Accumulated Amortization	(8.0)	(6.7)
Asset Improvements [Member] \| KCPL [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	15.1	13.6
Finite-Lived Intangible Assets, Accumulated Amortization	$ (2.7)	$ (1.8)

Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Increase in asset retirement obligations due to CCR regulations		$ 42.1
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	$ 316.0	275.9
Additions	0.0	1.6
Revision in timing and/or estimates	(1.3)	42.1
Settlements	(28.5)	(17.4)
Accretion	14.9	13.8
Asset Retirement Obligation, Ending Balance	$ 301.1	316.0
Asset Retirement Obligations, Liability Not Recognized	certain wiring used in Great Plains Energy's and KCP&L's generating stations include asbestos insulation, which would require special handling if disturbed. Due to the inability to reasonably estimate the quantities or the amount of disturbance that will be necessary during dismantlement at the end of the life of a plant, the fair value of this ARO cannot be reasonably estimated at this time. Management will continue to monitor the obligation and will recognize a liability in the period in which sufficient information becomes available to reasonably estimate its fair value.
Asset Retirement Obligation, Current	$ (38.6)	0.0
Total noncurrent asset retirement obligation	$ 262.5	316.0
KCPL Greater Missouri Operations [Member]
Asset Retirement Obligations, Description	GMO has AROs related to asbestos abatement, removal of storage tanks and closure and post-closure of ponds and landfills containing CCRs.
KCPL [Member]
Asset Retirement Obligations, Description	KCP&L has AROs related to decommissioning Wolf Creek, site remediation of its Spearville Wind Energy Facilities, asbestos abatement, removal of storage tanks and closure and post-closure of ponds and landfills containing coal combustion residuals (CCRs).
Increase in asset retirement obligations due to CCR regulations		40.1
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	$ 278.0	239.3
Additions	0.0	1.3
Revision in timing and/or estimates	0.3	40.1
Settlements	(25.5)	(15.0)
Accretion	13.5	12.3
Asset Retirement Obligation, Ending Balance	$ 266.3	278.0
Asset Retirement Obligations, Liability Not Recognized	certain wiring used in Great Plains Energy's and KCP&L's generating stations include asbestos insulation, which would require special handling if disturbed. Due to the inability to reasonably estimate the quantities or the amount of disturbance that will be necessary during dismantlement at the end of the life of a plant, the fair value of this ARO cannot be reasonably estimated at this time. Management will continue to monitor the obligation and will recognize a liability in the period in which sufficient information becomes available to reasonably estimate its fair value.
Asset Retirement Obligation, Current	$ (34.9)	0.0
Total noncurrent asset retirement obligation	$ 231.4	$ 278.0

Pension Plans and Other Employee Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2017
Amounts recognized in the consolidated balance sheets [Abstract]
Current pension and other post-retirement liability		$ (3.0)		$ (2.7)
Noncurrent pension liability and other post-retirement liability		(488.3)		(535.0)
Pension plans with the accumulated benefit obligation in excess of plans assets [Abstract]
Unfunded accumulated benefit obligation for GMO SERP				24.0
Segregated assets for GMO SERP				14.7
Employee Savings Plans [Abstract]
Defined contribution savings plan, cost of plan	$ 10.9	11.5	$ 10.6
KCPL [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Current pension and other post-retirement liability		(1.6)		(1.4)
Noncurrent pension liability and other post-retirement liability		(465.8)		(512.2)
Employee Savings Plans [Abstract]
Defined contribution savings plan, cost of plan	7.7	8.0	7.9
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	1,244.6	1,154.8
Service cost	44.2	42.0	45.3
Interest cost	53.5	52.9	50.3
Contributions by participants	0.0	0.0
Amendments	0.0	0.0
Actuarial (gain) loss	135.6	65.5
Benefits paid	(36.8)	(70.6)
Settlements and special termination benefits	(85.2)	0.0
Defined Benefit Plan, Benefit Obligation	1,355.9	1,244.6	1,154.8
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of the year	776.8	723.9
Actual return on plan assets	114.8	51.1
Contributions by employer and participants	76.9	69.8
Benefits paid	(34.5)	(68.0)
Settlements	(85.6)	0.0
Fair value of plan assets at end of the year	848.4	776.8	723.9
Funded status at end of year		(467.8)		(507.5)
Amounts recognized in the consolidated balance sheets [Abstract]
Non-current asset		0.0		0.0
Current pension and other post-retirement liability		(2.2)		(1.9)
Noncurrent pension liability and other post-retirement liability		(465.6)		(505.6)
Net amount recognized before regulatory treatment		(467.8)		(507.5)
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or Regulatory Asset Liability		476.9		492.2
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position		9.1		(15.3)
Amounts in accumulated other comprehensive income or regulatory asset/liability not yet recognized as a component of net periodic benefit cost [Abstract]
Actuarial (gain) loss		242.5		248.9
Prior service cost		3.2		2.5
Other		231.2		240.8
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or Regulatory Asset Liability		476.9		492.2
Components of net periodic benefit costs [Abstract]
Service cost	44.2	42.0	45.3
Interest cost	53.5	52.9	50.3
Expected return on plan assets	(51.2)	(49.2)	(51.7)
Prior service cost	0.7	0.7	0.8
Recognized net actuarial (gain)/loss	49.7	51.8	51.4
Transition obligation	0.0	0.0	0.0
Settlement and special termination benefits	16.3	0.0	0.0
Net periodic benefit costs before regulatory adjustment	113.2	98.2	96.1
Regulatory adjustment	(13.8)	(4.9)	(9.8)
Net periodic benefit costs	99.4	93.3	86.3
Defined Benefit Plan, Net Periodic Benefit Cost, Loss Due to Settlement, Accelerated Pension Distributions	15.9
Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income Regulatory Assets/Liabilities [Abstract]
Current year net (gain) loss	72.0	63.6	8.6
Amortization of gain (loss)	(65.6)	(51.8)	(51.4)
Prior service cost	0.0	0.0	0.0
Amortization of prior service cost	(0.7)	(0.7)	(0.8)
Amortization of transition obligation	0.0	0.0	0.0
Other regulatory activity	9.6	4.6	4.3
Total Recognized In Other Comprehensive Income Or Regulatory Asset/Liability	15.3	15.7	(39.3)
Total Recognized In Net Periodic Benefit Costs And Other Comprehensive Income Or Regulatory Asset/Liability	114.7	109.0	47.0
Estimated prior service cost that will be amortized in the next fiscal year	0.7
Net (gain) loss for the defined benefit plans that will be amortized in the next fiscal year	$ 45.7
Length Of Time For Amortization Of Net Actuarial Gains And Losses For Financial Reporting Purposes	rolling five-year average
Length Of Time For Amortization Of Net Actuarial Gains And Losses For Regulatory Reporting Purposes	ten years
Accumulated benefit obligation (ABO) for all defined benefit plans		1,090.2		1,169.8
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets, Benefit Obligation		1,244.6		1,355.9
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets, Fair Value of Plan Assets		776.8		848.4
Pension plans with the accumulated benefit obligation in excess of plans assets [Abstract]
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation		1,090.2		1,169.8
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Fair Value of Plan Assets		$ 776.8		848.4
Weighted average assumptions used to determine the benefit obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.31%			3.72%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		3.62%			3.62%
Defined Benefit Plan, Assumptions Used in Calculation, Description	The expected long-term rate of return on plan assets represents Great Plains Energy's estimate of the long-term return on plan assets and is based on historical and projected rates of return for current and planned asset classes in the plans' investment portfolios. Assumed projected rates of return for each asset class were selected after analyzing historical experience and future expectations of the returns of various asset classes. Based on the target asset allocation for each asset class, the overall expected rate of return for the portfolios was developed and adjusted for the effect of projected benefits paid from plan assets and future plan contributions.
Weighted average assumptions used to determine net costs [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.31%	4.54%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	6.73%	7.14%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.62%	3.62%
Contribute to plans in next year				84.0
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months				79.3
Defined Benefit Plan, Expected Future Benefit Payment, Year Two				82.2
Defined Benefit Plan, Expected Future Benefit Payment, Year Three				84.7
Defined Benefit Plan, Expected Future Benefit Payment, Year Four				86.0
Defined Benefit Plan, Expected Future Benefit Payment, Year Five				86.5
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter				459.9
Defined Benefit Plan, Target Allocation Percentage	The portfolios are invested, and periodically rebalanced, to achieve targeted allocations of approximately 33% U.S. large cap and small cap equity securities, 21% international equity securities, 36% fixed income securities, 7% real estate, 1% commodities and 2% hedge funds.
Defined Benefit Plan, Investment Strategies, Investment Fund Category	The investment strategy supports the objective of the fund, which is to earn the highest possible return on plan assets within a reasonable and prudent level of risk.
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	$ 130.1	$ 137.5
Service cost	2.1	2.6	3.3
Interest cost	5.4	6.1	6.8
Contributions by participants	6.0	5.3
Amendments	0.0	(10.1)
Actuarial (gain) loss	2.1	0.6
Benefits paid	(12.5)	(11.9)
Settlements and special termination benefits	0.0	0.0
Defined Benefit Plan, Benefit Obligation	133.2	130.1	137.5
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of the year	115.6	114.3
Actual return on plan assets	1.8	2.6
Contributions by employer and participants	10.4	10.2
Benefits paid	(12.0)	(11.5)
Settlements	0.0	0.0
Fair value of plan assets at end of the year	115.8	115.6	114.3
Funded status at end of year		(14.5)		(17.4)
Amounts recognized in the consolidated balance sheets [Abstract]
Non-current asset		9.0		12.8
Current pension and other post-retirement liability		(0.8)		(0.8)
Noncurrent pension liability and other post-retirement liability		(22.7)		(29.4)
Net amount recognized before regulatory treatment		(14.5)		(17.4)
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or Regulatory Asset Liability		(23.6)		(21.1)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position		(38.1)		(38.5)
Amounts in accumulated other comprehensive income or regulatory asset/liability not yet recognized as a component of net periodic benefit cost [Abstract]
Actuarial (gain) loss		(0.7)		2.8
Prior service cost		(8.0)		(8.0)
Other		(14.9)		(15.9)
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or Regulatory Asset Liability		(23.6)		(21.1)
Components of net periodic benefit costs [Abstract]
Service cost	2.1	2.6	3.3
Interest cost	5.4	6.1	6.8
Expected return on plan assets	(2.6)	(3.1)	(2.9)
Prior service cost	0.0	1.2	3.1
Recognized net actuarial (gain)/loss	(0.5)	(1.5)	0.2
Transition obligation	0.0	0.0	0.2
Settlement and special termination benefits	0.0	0.0	0.0
Net periodic benefit costs before regulatory adjustment	4.4	5.3	10.7
Regulatory adjustment	1.9	6.0	4.4
Net periodic benefit costs	6.3	11.3	15.1
Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income Regulatory Assets/Liabilities [Abstract]
Current year net (gain) loss	3.0	1.1	(20.6)
Amortization of gain (loss)	0.5	1.5	(0.2)
Prior service cost	0.0	(10.2)	(7.0)
Amortization of prior service cost	0.0	(1.2)	(3.1)
Amortization of transition obligation	0.0	0.0	(0.2)
Other regulatory activity	(1.0)	(5.4)	(4.4)
Total Recognized In Other Comprehensive Income Or Regulatory Asset/Liability	2.5	(14.2)	(35.5)
Total Recognized In Net Periodic Benefit Costs And Other Comprehensive Income Or Regulatory Asset/Liability	8.8	(2.9)	$ (20.4)
Net (gain) loss for the defined benefit plans that will be amortized in the next fiscal year	$ (0.2)
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets, Benefit Obligation		61.7		111.6
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets, Fair Value of Plan Assets		$ 38.3		81.5
Weighted average assumptions used to determine the benefit obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.20%			3.64%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		3.50%			3.50%
Weighted average assumptions used to determine net costs [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.20%	4.47%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	2.00%	2.54%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.50%	3.50%
Contribute to plans in next year				4.6
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months				9.2
Defined Benefit Plan, Expected Future Benefit Payment, Year Two				9.2
Defined Benefit Plan, Expected Future Benefit Payment, Year Three				9.6
Defined Benefit Plan, Expected Future Benefit Payment, Year Four				10.1
Defined Benefit Plan, Expected Future Benefit Payment, Year Five				10.4
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter				$ 55.6
Defined Benefit Plan, Investment Strategies, Investment Fund Category	The investment strategy supports the objective of the funds, which is to preserve capital, maintain sufficient liquidity and earn a consistent rate of return.
Health care cost trend (in hundredths)	6.80%	6.50%
Health care cost rate declining through	2027
Ultimate cost trend rate (in hundredths)	4.50%
Effect on total service and interest component, increase	$ 0.2
Effect on total service and interest component, decrease	(0.2)
Effect on post-retirement benefit obligation, increase	0.4
Effect on post-retirement benefit obligation, decrease	$ (0.3)
Wolf Creek [Member]
Defined Benefit Plan Disclosure [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share					47.00%
Wolf Creek [Member] \| KCPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	47.00%				47.00%

Equity Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares of common shares authorized (in shares)	8,000,000
Equity compensation expense	$ 6.3	$ 5.0	$ 4.0
Income tax benefit	$ 2.4	$ 1.6	$ 1.4
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility (in hundredths)	18.00%
Expected dividend yield (in hundredths)	3.80%
Risk-free interest rate (in hundredths)	1.58%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)	625,100
Granted (in shares)	236,433
Earned (in shares)	(212,992)
Forfeited (in shares)	(103,454)
Ending balance (in shares)	545,087	625,100
Weighted average beginning balance (in dollars per share)	$ 28.13
Weighted average granted (in dollars per share)	31.26	$ 31.41	$ 24.03
Weighted average earned (in dollars per share)	28.48
Weighted average forfeited (in dollars per share)	29.24
Weighted average ending balance (in dollars per share)	$ 29.12	$ 28.13
Total unrecognized compensation expense	$ 6.1
Remaining weighted-average contractual term (in years)	1 year 1 month
Fair value of performance shares earned and paid	$ 6.1	$ 7.4	$ 0.5
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)	249,672
Granted (in shares)	81,040
Vested (in shares)	(112,813)
Forfeited (in shares)	(25,497)
Ending balance (in shares)	192,402	249,672
Weighted average beginning balance (in dollars per share)	$ 27.20
Weighted average granted (in dollars per share)	28.68	$ 29.41	$ 25.89
Weighted average vested (in dollars per share)	26.92
Weighted average forfeited (in dollars per share)	28.10
Weighted average ending balance (in dollars per share)	$ 27.87	$ 27.20
Total unrecognized compensation expense	$ 2.1
Total fair value of shares vested	$ 3.0	$ 1.8	$ 2.2
Remaining weighted-average contractual term (in years)	1 year 2 months
KCPL [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 4.2	3.2	2.6
Income tax benefit	$ 1.6	$ 1.0	$ 0.9

Equity Compensation Equity Compensation Deferred Directors (Details) - Director [Member] - Director Deferred Share Units [Member]	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Director deferred share units [Roll Forward]
Director deferred share units, beginning balance (in shares) \| shares	138,587
Director deferred share units, issued (in shares) \| shares	23,435
Director deferred share units, converted (in shares) \| shares	(22,871)
Director deferred share units, ending balance (in shares) \| shares	139,151
Weighted-average grant date fair value, director deferred share units, beginning balance (in dollars per share) \| $ / shares	$ 23.96
Weighted-average grant date fair value, director deferred share units, issued (in dollars per share) \| $ / shares	30.09
Weighted average grant date fair value director deferred share units, converted \| $ / shares	21.81
Weighted-average grant date fair value, director deferred share units, ending balance (in dollars per share) \| $ / shares	$ 25.35

Short-term Borrowings and Short-term Bank Lines of Credit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Jul. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Amount of outstanding cash borrowings	$ 11.0		$ 0.0
Commercial paper outstanding	376.8		334.8
KCPL Greater Missouri Operations [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 209.3		$ 201.9
Weighted-average interest rate from outstanding borrowings	1.85%		1.02%
KCPL Greater Missouri Operations [Member] \| Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 450.0
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200.0
Line of Credit Facility, Covenant Terms	A default by GMO or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0.0		$ 0.0
Amount of letters of credit outstanding	2.1		1.9
KCPL [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 167.5		$ 132.9
Weighted-average interest rate from outstanding borrowings	1.95%		0.98%
KCPL [Member] \| Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 600.0
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200.0
Line of Credit Facility, Covenant Terms	A default by KCP&L on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, KCP&L is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0.0		$ 0.0
Amount of letters of credit outstanding	2.7		2.8
Great Plains Energy [Member]
Short-term Debt [Line Items]
Amount of outstanding cash borrowings	11.0		0.0
Great Plains Energy [Member] \| Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200.0
Credit facility expiration date	Oct. 31, 2019
Maximum borrowing capacity with transfer of unused commitments	$ 400.0
Line of Credit Facility, Covenant Terms	A default by Great Plains Energy or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility. Under the terms of this facility, Great Plains Energy is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 11.0		0.0
Weighted-average interest rate from outstanding borrowings	2.94%
Amount of letters of credit outstanding	$ 1.0		$ 1.0
Great Plains Energy [Member] \| Bridge Loan [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	8,017.0
Amount of bridge facility, as amended	$ 864.5	$ 864.5

Long-Term Debt (Details) - USD ($) $ in Millions	1 Months Ended			12 Months Ended
Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2017	Jul. 31, 2017	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2017	Mar. 31, 2017
Debt Instrument [Line Items]
Current maturities					$ (382.1)		$ (351.1)
Long-term debt excluding current maturities					3,365.2		3,312.6
Amortization of Financing Costs				$ 29.9	33.8	$ 4.1
Long-term Debt, Fiscal Year Maturity [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months							351.1
Long-term Debt, Maturities, Repayments of Principal in Year Two							401.1
Long-term Debt, Maturities, Repayments of Principal in Year Three							1.1
Long-term Debt, Maturities, Repayments of Principal in Year Four							432.0
Long-term Debt, Maturities, Repayments of Principal in Year Five							287.5
GMO Senior Notes [Abstract]
Loss on extinguishment of debt				82.8	0.0	0.0
GPE 4.3 Billion Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross							4,300.0
Other Consolidated Entities [Member]
Debt Instrument [Line Items]
Current maturities					(101.1)		(1.1)
Unamortized discount and premium, net and debt issuance costs					(1.8)		(1.5)
Amortization of Financing Costs				26.9	30.6	1.1
Other Consolidated Entities [Member] \| Bridge Loan [Member]
Debt Instrument [Line Items]
Amortization of Financing Costs				23.6	29.6
KCPL [Member]
Debt Instrument [Line Items]
Current maturities					(281.0)		(350.0)
Unamortized discount and premium, net and debt issuance costs					(15.4)		(17.2)
Long-term debt excluding current maturities					2,284.0		2,232.2
Amortization of Financing Costs				$ 3.0	3.2	3.0
Long-term Debt, Fiscal Year Maturity [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months							350.0
Long-term Debt, Maturities, Repayments of Principal in Year Two							400.0
Long-term Debt, Maturities, Repayments of Principal in Year Three							0.0
Long-term Debt, Maturities, Repayments of Principal in Year Four							0.0
Long-term Debt, Maturities, Repayments of Principal in Year Five							0.0
KCPL [Member] \| Secured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					510.5		479.5
KCPL [Member] \| Secured Debt [Member] \| General Mortgage bonds Series 2009A due 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					400.0		400.0
Debt Instrument, Maturity Date				Dec. 31, 2019
Interest rates (in hundredths)								7.15%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)								8.59%
KCPL [Member] \| Secured Debt [Member] \| General Mortgage bonds EIRR series 2005 [Member]
Debt Instrument [Line Items]
EIRR bonds repurchased and held					50.0		50.0
KCPL Municipal Bond Insurance Policies [Abstract]
Insurance Agreement Covenant Indebtedness To Total Capitalization Ratio Maximum				75.00%
Principal outstanding covered by insurance policies							50.0
Insurance Agreement Covenant Description				The insurance agreements contain a covenant that the indebtedness to total capitalization ratio of KCP&L and its consolidated subsidiaries will not be greater than 0.68 to 1.00.
Insurance Agreement Covenant Compliance				in compliance
Proportion Of Secured Debt To Total Indebtedness Based On Bond Ratings Maximum In Hundredths				50.00%
Aggregate Amount Of Outstanding General Mortgage Bonds As Percentage Of Total Capitalization Maximum In Hundredths				10.00%
KCPL [Member] \| Secured Debt [Member] \| General Mortgage Bonds EIRR Due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					110.5		79.5
EIRR bonds repurchased and held					21.9		21.9
Debt Instrument, Maturity Date				Dec. 31, 2023
Interest rates (in hundredths)								2.95%
KCPL Municipal Bond Insurance Policies [Abstract]
Insurance Agreement Covenant Indebtedness To Total Capitalization Ratio Maximum				75.00%
Principal outstanding covered by insurance policies							21.9
Insurance Agreement Covenant Description				The insurance agreements contain a covenant that the indebtedness to total capitalization ratio of KCP&L and its consolidated subsidiaries will not be greater than 0.68 to 1.00
Insurance Agreement Covenant Compliance				in compliance
Proportion Of Secured Debt To Total Indebtedness Based On Bond Ratings Maximum In Hundredths				50.00%
Aggregate Amount Of Outstanding General Mortgage Bonds As Percentage Of Total Capitalization Maximum In Hundredths				10.00%
KCPL [Member] \| Secured Debt [Member] \| General Mortgage Bonds EIRR Due 2017 [Member]
Debt Instrument [Line Items]
Repayments of Long-Term Debt		$ 31.0
KCPL [Member] \| Senior Notes [Member] \| Senior notes due 2017 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					250.0		0.0
Interest rates (in hundredths)			5.85%					5.85%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)								5.72%
Repayments of Long-Term Debt			$ 250.0
KCPL [Member] \| Senior Notes [Member] \| Senior notes due 2018 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					350.0		350.0
Debt Instrument, Maturity Date				Dec. 31, 2018
Interest rates (in hundredths)								6.375%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)								7.49%
KCPL [Member] \| Senior Notes [Member] \| Senior Notes due 2023 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					300.0		300.0
Debt Instrument, Maturity Date				Dec. 31, 2023
Interest rates (in hundredths)								3.15%
KCPL [Member] \| Senior Notes [Member] \| Senior Notes due 2025 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					350.0		350.0
Debt Instrument, Maturity Date				Dec. 31, 2025
Interest rates (in hundredths)								3.65%
KCPL [Member] \| Senior Notes [Member] \| Senior notes due 2035 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					250.0		250.0
Debt Instrument, Maturity Date				Dec. 31, 2035
Interest rates (in hundredths)								6.05%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)								5.78%
KCPL [Member] \| Senior Notes [Member] \| Senior Notes Due 2041 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					400.0		400.0
Debt Instrument, Maturity Date				Dec. 31, 2041
Interest rates (in hundredths)								5.30%
KCPL [Member] \| Senior Notes [Member] \| Senior Notes Due 2047 KCPL [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 300.0		0.0		300.0
Debt Instrument, Maturity Date			Dec. 31, 2047	Dec. 31, 2047
Interest rates (in hundredths)			4.20%					4.20%
KCPL [Member] \| Unsecured Debt [Member] \| EIRR Bonds Series 2007A and 2007B due 2035 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					146.5		146.5
Debt Instrument, Maturity Date				Dec. 31, 2035
Variable rate (in hundredths)								1.329%
KCPL [Member] \| Unsecured Debt [Member] \| EIRR bonds 2.875 percent Series 2008 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					23.4		23.4
Debt Instrument, Maturity Date				Dec. 31, 2038
Interest rates (in hundredths)								2.875%
KCPL Greater Missouri Operations [Member] \| Secured Debt [Member] \| First Mortgage Bonds due through 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					5.7		4.6
Debt Instrument Maturity Date Range End				Dec. 31, 2021
Debt Instrument Maturity Date Range Start				Dec. 31, 2018
Interest rates (in hundredths)								9.44%
KCPL Greater Missouri Operations [Member] \| Senior Notes [Member] \| Senior notes 8.27 percent series due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					80.9		80.9
Debt Instrument, Maturity Date				Dec. 31, 2021
Interest rates (in hundredths)								8.27%
KCPL Greater Missouri Operations [Member] \| Senior Notes [Member] \| Senior Notes Series A due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					125.0		125.0
Debt Instrument, Maturity Date				Dec. 31, 2025
Interest rates (in hundredths)								3.49%
GMO Senior Notes [Abstract]
Debt Instrument, Covenant Description				GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement
Debt Instrument, Covenant Compliance				in compliance
KCPL Greater Missouri Operations [Member] \| Senior Notes [Member] \| Senior Notes Series B due 2033 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					75.0		75.0
Debt Instrument, Maturity Date				Dec. 31, 2033
Interest rates (in hundredths)								4.06%
GMO Senior Notes [Abstract]
Debt Instrument, Covenant Description				GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement.
Debt Instrument, Covenant Compliance				in compliance
KCPL Greater Missouri Operations [Member] \| Senior Notes [Member] \| Senior Notes Series C due 2043 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					150.0		150.0
Debt Instrument, Maturity Date				Dec. 31, 2043
Interest rates (in hundredths)								4.74%
GMO Senior Notes [Abstract]
Debt Instrument, Covenant Description				GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the agreement, not greater than 0.65 to 1.00 at all times. In addition, GMO's priority debt, as defined in the agreement, cannot exceed 15% of consolidated tangible net worth, as defined in the agreement.
Debt Instrument, Covenant Compliance				in compliance
KCPL Greater Missouri Operations [Member] \| Medium-term Notes [Member] \| Medium term notes 7.33 percent series due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					3.0		3.0
Debt Instrument, Maturity Date				Dec. 31, 2023
Interest rates (in hundredths)								7.33%
KCPL Greater Missouri Operations [Member] \| Medium-term Notes [Member] \| Medium term notes 7.17 percent series due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					7.0		7.0
Debt Instrument, Maturity Date				Dec. 31, 2023
Interest rates (in hundredths)								7.17%
Great Plains Energy [Member]
Debt Instrument [Line Items]
Current maturities					(100.0)		0.0
Long-term debt excluding current maturities					638.2		638.2
GMO Senior Notes [Abstract]
Loss on extinguishment of debt				$ 82.8	0.0	$ 0.0
Great Plains Energy [Member] \| GPE 4.3 Billion Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 4,300.0							$ 4,300.0
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					100.0		0.0
Interest rates (in hundredths)				6.875%				6.875%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)								7.33%
Repayments of Long-Term Debt	$ 100.0
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					350.0		350.0
Debt Instrument, Maturity Date				Dec. 31, 2021
Interest rates (in hundredths)								4.85%
Great Plains Energy [Member] \| Senior Notes [Member] \| Senior Notes 5.292 Percent Series Due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					$ 287.5		$ 287.5
Debt Instrument, Maturity Date				Dec. 31, 2022
Interest rates (in hundredths)								5.292%
Great Plains Energy [Member] \| Senior Notes [Member] \| GPE 4.3 Billion Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross									$ 4,300.0
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed		101.00%
GMO Senior Notes [Abstract]
Total Redemption Cost		$ 4,400.1
Loss on extinguishment of debt		$ 82.8

Common Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
Common Shareholders' Equity [Line Items]
Common Stock, Shares Authorized		600,000,000	600,000,000		600,000,000
Common Stock Shares Authorized Prior to Amended Articles of Incorporation					250,000,000
Number of shares available for grant under the Dividend Reinvestment and Direct Stock Purchase Plan (in shares)		900,000
Number of shares available under the defined contribution savings plan (in shares)		500,000
Restrictions on the payment of common stock dividends		Great Plains Energy's articles of incorporation restrict the payment of common stock dividends in the event common equity is 25% or less of total capitalization. Certain conditions in the MPSC and KCC orders authorizing the holding company structure require Great Plains Energy and KCP&L to maintain consolidated common equity of at least 30% and 35%, respectively, of total capitalization (including only the amount of short-term debt in excess of the amount of construction work in progress). Under the Federal Power Act, KCP&L and GMO generally can pay dividends only out of retained earnings. The revolving credit agreements of Great Plains Energy, KCP&L and GMO and the note purchase agreement for GMO's Series A, B and C Senior Notes contain a covenant requiring the respective company to maintain a consolidated indebtedness to consolidated total capitalization ratio of not more than 0.65 to 1.00 at all times. Under the Amended Merger Agreement, Great Plains Energy is also restricted from paying a quarterly common stock dividend in excess of $0.275 per share without the consent of Westar.
Restricted net assets of subsidiaries		$ 2,800.0
Gross Proceeds from Issuance of Common Stock		$ 2.9	$ 1,603.7	$ 3.0
Common Stock [Member]
Common Shareholders' Equity [Line Items]
Shares Issued, Price Per Share	$ 26.45
Gross Proceeds from Issuance of Common Stock	$ 1,600.0
Net Proceeds from Issuance of Common Stock	$ 1,550.0
Stock Issued During Period, Shares, New Issues	60,500,000	322,618	60,974,205	250,863

Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended		12 Months Ended
	May 29, 2016	Jul. 31, 2017	Oct. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Mandatory Convertible Preferred Stock [Abstract]
Loss on Series B Preferred Stock dividend make-whole provisions				$ 124.8	$ 0.0	$ 0.0
Payments for Repurchase of Redeemable Preferred Stock				963.4	40.1	$ 0.0
Preferred Stock, Value, Issued				$ 0.0	$ 836.2
No Par Preference Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized				11,000,000	11,000,000
Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Cumulative preferred stock par value (in dollars per share)				$ 100
Preferred Stock, Shares Authorized				390,000
Cumulative No Par Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized				1,600,000
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Purchase Agreement, Proceeds	$ 750.0	$ 750.0		$ 750.0
Preferred Stock, Dividend Rate, Percentage				7.25%
Mandatory Convertible Preferred Stock [Abstract]
Preferred Shares To Be Issued, Stock Purchase Agreement, Series A Preferred Stock	750,000			750,000
Previously deferred offering costs written off		$ 15.0
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage				7.00%	7.00%
Mandatory Convertible Preferred Stock [Abstract]
Preferred Stock, Liquidation Preference Per Share				$ 1,000.00	$ 1,000.00
Loss on Series B Preferred Stock dividend make-whole provisions				$ 124.8
Preferred Stock Redemption Premium				2.4
Payments for Repurchase of Redeemable Preferred Stock				963.4
Preferred Stock, Value, Issued				$ 836.2
Depositary Shares [Member]
Mandatory Convertible Preferred Stock [Abstract]
Stock Issued During Period, Shares, New Issues			17,300,000
Gross Proceeds from Issuance of Depositary Shares			$ 862.5
Depositary Shares, Liquidation Preference Per Share				$ 50
Shares Issued, Price Per Share			$ 50
Net Proceeds from Issuance of Depositary Shares			$ 836.2

Commitments and Contingencies Commitments and Contingencies Contractual Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Lease Expense [Abstract]
Lease expense	$ 14.2	$ 15.0	$ 16.8
Operating Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	12.1
Operating Leases, Future Minimum Payments, Due in Two Years	9.3
Operating Leases, Future Minimum Payments, Due in Three Years	9.7
Operating Leases, Future Minimum Payments, Due in Four Years	9.7
Operating Leases, Future Minimum Payments, Due in Five Years	9.5
Operating Leases, Future Minimum Payments, Due Thereafter	101.0
Operating Leases, Future Minimum Payments Due, Total	151.3
Capital Leases [Abstract]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	0.4
Capital Leases, Future Minimum Payments Due in Two Years	0.4
Capital Leases, Future Minimum Payments Due in Three Years	0.4
Capital Leases, Future Minimum Payments Due in Four Years	0.4
Capital Leases, Future Minimum Payments Due in Five Years	0.4
Capital Leases, Future Minimum Payments Due Thereafter	2.7
Capital Leases, Future Minimum Payments Due, Total	4.7
Total Commitments [Abstract]
Total Commitments, Due in Next Twelve Months	291.1
Total Commitments, Due within Two Years	251.8
Total Commitments, Due within Three Years	131.4
Total Commitments, Due within Four Years	68.1
Total Commitments, Due within Five Years	97.3
Total Commitments, Due Thereafter	634.9
Total Commitments Due	1,474.6
Public Utilities, Inventory, Fuel [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	210.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	180.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years	67.3
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5.1
Unrecorded Unconditional Purchase Obligation, Due within Five Years	37.4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	80.7
Unrecorded Unconditional Purchase Obligation, Total	581.0
Purchased Power [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	47.3
Unrecorded Unconditional Purchase Obligation, Due within Two Years	47.3
Unrecorded Unconditional Purchase Obligation, Due within Three Years	47.3
Unrecorded Unconditional Purchase Obligation, Due within Four Years	47.4
Unrecorded Unconditional Purchase Obligation, Due within Five Years	47.6
Unrecorded Unconditional Purchase Obligation, Due after Five Years	414.6
Unrecorded Unconditional Purchase Obligation, Total	651.5
Other purchase commitments [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	20.9
Unrecorded Unconditional Purchase Obligation, Due within Two Years	14.7
Unrecorded Unconditional Purchase Obligation, Due within Three Years	6.7
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5.5
Unrecorded Unconditional Purchase Obligation, Due within Five Years	2.4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	35.9
Unrecorded Unconditional Purchase Obligation, Total	86.1
KCPL [Member]
Lease Expense [Abstract]
Lease expense	13.1	$ 13.7	$ 15.0
Operating Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	11.3
Operating Leases, Future Minimum Payments, Due in Two Years	9.3
Operating Leases, Future Minimum Payments, Due in Three Years	9.7
Operating Leases, Future Minimum Payments, Due in Four Years	9.7
Operating Leases, Future Minimum Payments, Due in Five Years	9.5
Operating Leases, Future Minimum Payments, Due Thereafter	101.0
Operating Leases, Future Minimum Payments Due, Total	150.5
Capital Leases [Abstract]
Capital Leases, Future Minimum Payments Due, Next Twelve Months	0.2
Capital Leases, Future Minimum Payments Due in Two Years	0.2
Capital Leases, Future Minimum Payments Due in Three Years	0.2
Capital Leases, Future Minimum Payments Due in Four Years	0.2
Capital Leases, Future Minimum Payments Due in Five Years	0.2
Capital Leases, Future Minimum Payments Due Thereafter	1.4
Capital Leases, Future Minimum Payments Due, Total	2.4
Total Commitments [Abstract]
Total Commitments, Due in Next Twelve Months	243.8
Total Commitments, Due within Two Years	216.8
Total Commitments, Due within Three Years	102.3
Total Commitments, Due within Four Years	54.5
Total Commitments, Due within Five Years	83.8
Total Commitments, Due Thereafter	504.3
Total Commitments Due	1,205.5
Reimbursement By Other Owners per Year (2018)	1.2
Reimbursements by Other Owners per Year (2019 to 2025)	0.4
Reimbursements by Other Owners Total	4.0
KCPL [Member] \| Public Utilities, Inventory, Fuel [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	177.5
Unrecorded Unconditional Purchase Obligation, Due within Two Years	159.8
Unrecorded Unconditional Purchase Obligation, Due within Three Years	51.8
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5.1
Unrecorded Unconditional Purchase Obligation, Due within Five Years	37.4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	80.7
Unrecorded Unconditional Purchase Obligation, Total	512.3
KCPL [Member] \| Purchased Power [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	34.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years	34.8
Unrecorded Unconditional Purchase Obligation, Due within Three Years	34.8
Unrecorded Unconditional Purchase Obligation, Due within Four Years	34.9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	35.1
Unrecorded Unconditional Purchase Obligation, Due after Five Years	289.8
Unrecorded Unconditional Purchase Obligation, Total	464.2
KCPL [Member] \| Other purchase commitments [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	20.0
Unrecorded Unconditional Purchase Obligation, Due within Two Years	12.7
Unrecorded Unconditional Purchase Obligation, Due within Three Years	5.8
Unrecorded Unconditional Purchase Obligation, Due within Four Years	4.6
Unrecorded Unconditional Purchase Obligation, Due within Five Years	1.6
Unrecorded Unconditional Purchase Obligation, Due after Five Years	31.4
Unrecorded Unconditional Purchase Obligation, Total	$ 76.1

Commitments and Contingencies Environmental Matters (Details) T in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) T	Dec. 31, 2016 USD ($)
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	$ 14.6
Estimate Of Environmental Capital Expenditures In Two Years	2.8
Estimate Of Environmental Capital Expenditures In Three Years	7.7
Estimate Of Environmental Capital Expenditures In Four Years	20.1
Estimate Of Environmental Capital Expenditures In Five Years	$ 63.1
Climate Change [Abstract]
CO2 produced per year (in millions of tons) \| T	17
EPA nationwide CO2 emission reductions by 2030	32.00%
Remediation [Abstract]
Accrued environmental remediation expenses	$ 1.5	$ 1.4
KCPL Greater Missouri Operations [Member]
Remediation [Abstract]
Estimated amount of insurance proceeds available to cover qualified remediation expenses	1.6
KCPL [Member]
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	14.5
Estimate Of Environmental Capital Expenditures In Two Years	2.8
Estimate Of Environmental Capital Expenditures In Three Years	7.7
Estimate Of Environmental Capital Expenditures In Four Years	20.1
Estimate Of Environmental Capital Expenditures In Five Years	$ 63.1
Climate Change [Abstract]
CO2 produced per year (in millions of tons) \| T	13
Remediation [Abstract]
Accrued environmental remediation expenses	$ 0.3	$ 0.3

Guarantees (Details) $ in Millions	12 Months Ended
Guarantees (Details) $ in Millions	Dec. 31, 2017 USD ($)
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 133.5
Guarantor Obligations, Origin and Purpose	In the ordinary course of business, Great Plains Energy and certain of its subsidiaries enter into various agreements providing financial or performance assurance to third parties on behalf of certain subsidiaries. Such agreements include, for example, guarantees and letters of credit. These agreements are entered into primarily to support or enhance the creditworthiness otherwise attributed to a subsidiary on a stand-alone basis, thereby facilitating the extension of sufficient credit to accomplish the subsidiary's intended business purposes.
Direct Guarantee [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 38.0
Guarantor Obligations, Term	expire in 2018
Guarantor Obligations, Origin and Purpose	direct guarantees to GMO counterparties
Guarantee of Indebtedness of Others [Member] \| Long-term Debt [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 95.5
Guarantor Obligations, Term	maturity dates ranging from 2018 to 2023
Guarantor Obligations, Origin and Purpose	guarantee of GMO long-term debt
Guarantee of Indebtedness of Others [Member] \| Commercial Paper [Member]
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 209.3
Guarantor Obligations, Origin and Purpose	guaranteed GMO's commercial paper program

Related Party Transactions and Relationships (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
KCPL [Member] \| Money Pool [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 0.0	$ 0.0
KCPL [Member] \| KCPL Greater Missouri Operations [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	65.8	64.6
KCPL [Member] \| KCPL Greater Missouri Operations [Member] \| Operating Expenses and Capital Costs Billed [Member]
Related Party Transaction [Line Items]
Operating expenses and capital costs billed from KCPL to GMO	196.3	194.4	$ 183.6
KCPL [Member] \| Great Plains Energy [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 18.9	$ 2.6
Iatan No 1 And 2 [Member] \| KCPL Greater Missouri Operations [Member]
Related Party Transaction [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	18.00%

Fair Value Measurements Level 3 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Loss on Series B Preferred Stock dividend make-whole provisions	$ (124.8)	$ 0.0	$ 0.0
Derivative Financial Instruments, Assets [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance net asset (liability)	79.3	0.0
Net asset at December 31	91.4	79.3	$ 0.0
Derivative Financial Instruments, Assets [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member] \| Non-Operating Income [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	14.0	0.0
Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30:	14.0	0.0
Derivative Financial Instruments, Assets [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member] \| Interest Charges [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	(1.9)	79.3
Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30:	(1.9)	79.3
Derivative Financial Instruments, Liabilities [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Settlements	124.8	0.0
Derivative Financial Instruments, Liabilities [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member] \| Loss On Series B Preferred Stock Dividend Make-Whole Provisions [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	$ (124.8)	$ 0.0

Fair Value Measurements Fair Value Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jul. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)
KCPL Greater Missouri Operations [Member]
SERP rabbi trust [Abstract]
Alternative Investment, Fair Value Disclosure	$ 14.7	$ 16.0
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	3,700.0	3,800.0
Carrying (Reported) Amount, Fair Value Disclosure [Member] \| KCPL [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	2,600.0	2,600.0
Fair Value, Measurements, Recurring [Member]
Fair value of financial instruments [Abstract]
Derivative Asset, Fair Value, Gross Asset	91.4	79.3
GPE 4.3 Billion Senior Notes [Member]
Fair value of financial instruments [Abstract]
Long-term Debt, Gross	4,300.0
GPE 4.3 Billion Senior Notes [Member] \| Great Plains Energy [Member]
Fair value of financial instruments [Abstract]
Long-term Debt, Gross			$ 4,300.0	$ 4,300.0
Fair Value, Inputs, Level 2 [Member] \| Estimate of Fair Value Measurement [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	4,000.0	4,000.0
Fair Value, Inputs, Level 2 [Member] \| Estimate of Fair Value Measurement [Member] \| KCPL [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	2,800.0	2,700.0
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Fair value of financial instruments [Abstract]
Derivative Asset, Fair Value, Gross Asset	0.0	0.0
Interest Rate Contract [Member]
Fair value of financial instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	$ 12.1	$ 79.3
Fair Value Inputs, Contingency Factor, Interest Rate Derivative	0.35	0.35
Derivative Asset, Fair Value, Gross Asset	$ 91.4	$ 79.3
Interest Rate Contract [Member] \| Great Plains Energy [Member]
Fair value of financial instruments [Abstract]
Notional Contract Amount					$ 4,400.0
Derivatives, Interest Rate Swaps, Finalized Settlement Value				$ 140.6
Interest Rate Contract [Member] \| Non-Operating Income [Member]
Fair value of financial instruments [Abstract]
Derivative, Gain (Loss) on Derivative, Net	$ 14.0

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (6.6)	$ (12.0)
Other comprehensive income (loss) before reclassifications	(0.9)	(0.7)
Amounts reclassified from accumulated other comprehensive loss	5.3	6.1
Net current period other comprehensive income	4.4	5.4	$ 6.7
Ending balance	(2.2)	(6.6)	(12.0)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4.5)	(10.1)
Other comprehensive income (loss) before reclassifications	0.0	0.0
Amounts reclassified from accumulated other comprehensive loss	4.9	5.6
Net current period other comprehensive income	4.9	5.6
Ending balance	0.4	(4.5)	(10.1)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(2.1)	(1.9)
Other comprehensive income (loss) before reclassifications	(0.9)	(0.7)
Amounts reclassified from accumulated other comprehensive loss	0.4	0.5
Net current period other comprehensive income	(0.5)	(0.2)
Ending balance	(2.6)	(2.1)	(1.9)
KCPL [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4.2)
Net current period other comprehensive income	4.6	5.4	5.3
Ending balance	0.4	(4.2)
KCPL [Member] \| Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4.2)	(9.6)
Amounts reclassified from accumulated other comprehensive loss	4.6	5.4
Net current period other comprehensive income	4.6	5.4
Ending balance	$ 0.4	$ (4.2)	$ (9.6)

Accumulated Other Comprehensive Income (Loss) Reclassification (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges									$ (290.7)	$ (161.5)	$ (199.3)
Utility operating and maintenance expenses									(754.2)	(759.5)	(724.8)
Income (loss) before income tax (expense) benefit and income from equity investments									124.6	460.2	334.5
Income tax (expense) benefit									(233.3)	(172.2)	(122.7)
Net income (loss)	$ (100.1)	$ 10.5	$ (7.0)	$ (9.6)	$ 98.0	$ 133.6	$ 32.0	$ 26.4
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)									(5.3)	(6.1)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income tax (expense) benefit and income from equity investments									(7.9)	(9.2)
Income tax (expense) benefit									3.0	3.6
Net income (loss)									(4.9)	(5.6)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member] \| Interest Rate Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges									(7.9)	(9.2)
Accumulated Defined Benefit Plans Adjustment [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Utility operating and maintenance expenses									(0.7)	(0.8)
Income (loss) before income tax (expense) benefit and income from equity investments									(0.7)	(0.8)
Income tax (expense) benefit									0.3	0.3
Net income (loss)									(0.4)	(0.5)
KCPL [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges									(138.8)	(139.4)	(135.6)
Utility operating and maintenance expenses									(506.4)	(525.8)	(494.2)
Income (loss) before income tax (expense) benefit and income from equity investments									308.0	346.9	229.6
Income tax (expense) benefit									(128.2)	(121.9)	$ (76.8)
Net income (loss)	$ 1.9	$ 114.1	$ 49.6	$ 14.2	$ 16.8	$ 117.7	$ 65.9	$ 24.6
KCPL [Member] \| Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income tax (expense) benefit and income from equity investments									(7.5)	(8.8)
Income tax (expense) benefit									2.9	3.4
Net income (loss)									(4.6)	(5.4)
KCPL [Member] \| Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] \| Reclassification out of Accumulated Other Comprehensive Income [Member] \| Interest Rate Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges									$ (7.5)	$ (8.8)

Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
Income Tax Expense (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income taxes
Federal	$ (1.7)	$ 0.3	$ (0.2)
State	1.0	0.7	(1.1)
Total	(0.7)	1.0	(1.3)
Deferred income taxes
Federal	223.5	140.6	96.9
State	11.9	29.5	28.0
Total	235.4	170.1	124.9
Investment tax credit
Deferral	0.0	2.5	0.5
Amortization	(1.4)	(1.4)	(1.4)
Total	(1.4)	1.1	(0.9)
Income tax expense	233.3	$ 172.2	$ 122.7
Federal Deferred Income Tax Expense, Impact of Tax Reform	$ 130.3
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	0.10%	(0.10%)	0.00%
Amortization of investments tax credits (in hundredths)	(1.10%)	(0.30%)	(0.40%)
Federal income tax credits (in hundredths)	(5.80%)	(2.60%)	(4.10%)
State income taxes (in hundredths)	8.30%	4.20%	4.00%
Transaction costs (in hundredths)	42.50%	0.90%	0.00%
Valuation allowance	8.90%	0.00%	1.50%
Federal tax rate change (in hundredths)	95.30%	0.00%	0.00%
Other (in hundredths)	0.30%	0.20%	0.50%
Effective income tax rate (in hundredths)	183.50%	37.30%	36.50%
KCPL [Member]
Current income taxes
Federal	$ 37.4	$ 24.8	$ (18.7)
State	8.3	4.7	(3.4)
Total	45.7	29.5	(22.1)
Deferred income taxes
Federal	74.7	76.4	81.9
State	8.8	17.0	17.5
Total	83.5	93.4	99.4
Investment tax credit
Deferral	0.0	0.0	0.5
Amortization	(1.0)	(1.0)	(1.0)
Total	(1.0)	(1.0)	(0.5)
Income tax expense	$ 128.2	$ 121.9	$ 76.8
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	(0.10%)	(0.30%)	0.00%
Amortization of investments tax credits (in hundredths)	(0.30%)	(0.30%)	(0.50%)
Federal income tax credits (in hundredths)	(2.40%)	(3.10%)	(5.60%)
State income taxes (in hundredths)	3.80%	4.10%	4.00%
Valuation allowance	0.40%	0.00%	0.30%
Federal tax rate change (in hundredths)	5.30%	0.00%	0.00%
Other (in hundredths)	(0.10%)	(0.20%)	0.30%
Effective income tax rate (in hundredths)	41.60%	35.20%	33.50%

Taxes Deferred Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets (Liabilities), Net of Valuation Allowance, Noncurrent Classification [Abstract]
Plant related	$ (1,549.0)	$ (2,107.6)
Income taxes on future regulatory refunds (recoveries)	236.0
Income taxes on future regulatory refunds (recoveries)		(148.7)
Derivative instruments	(19.2)	(17.0)
Pension and post-retirement benefits	9.4	10.5
SO2 emission allowance sales	14.9	24.1
Fuel recovery mechanisms	(17.9)	(22.3)
Tax credit carryforwards	279.8	271.1
Customer demand programs	(17.4)	(34.3)
Solar rebates	(15.2)	(27.3)
Net operating loss carryforward	473.0	718.0
Other	6.9	20.2
Net noncurrent deferred income tax liability before valuation allowance	(598.7)	(1,313.3)
Valuation allowance	(23.0)	(16.4)
Net noncurrent deferred income tax liability	(621.7)	(1,329.7)
Net deferred income tax liability	(621.7)	(1,329.7)
Deferred Tax Assets (Liabilities), Gross [Abstract]
Gross deferred income tax assets	2,017.4	1,360.9
Gross deferred income tax liabilities	(2,639.1)	(2,690.6)
Net deferred income tax liability	(621.7)	(1,329.7)
KCPL [Member]
Deferred Tax Assets (Liabilities), Net of Valuation Allowance, Noncurrent Classification [Abstract]
Plant related	(1,114.9)	(1,492.2)
Income taxes on future regulatory refunds (recoveries)	179.1
Income taxes on future regulatory refunds (recoveries)		(123.9)
Derivative instruments	1.6	8.5
Pension and post-retirement benefits	28.6	38.6
SO2 emission allowance sales	15.0	24.1
Fuel recovery mechanisms	(15.9)	(27.2)
Tax credit carryforwards	185.8	177.4
Customer demand programs	(11.7)	(21.8)
Solar rebates	(5.8)	(11.4)
Net operating loss carryforward	131.2	198.3
Other		1.3
Other	(9.1)
Net noncurrent deferred income tax liability before valuation allowance	(616.1)	(1,228.3)
Valuation allowance	0.0	0.0
Net noncurrent deferred income tax liability	(616.1)	(1,228.3)
Net deferred income tax liability	(616.1)	(1,228.3)
Deferred Tax Assets (Liabilities), Gross [Abstract]
Gross deferred income tax assets	1,261.5	747.7
Gross deferred income tax liabilities	(1,877.6)	(1,976.0)
Net deferred income tax liability	$ (616.1)	$ (1,228.3)

Taxes Net Operating Loss Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 382.0	$ 643.8
Amount of Net Operating Losses related to business acquisition	179.3	306.2
Net operating losses year of origination [Abstract]
Net operating loss carryforwards originating in 2003	9.5
Net operating loss carryfowards originating in 2004	91.4
Net operating loss carryfowards originating in 2005	44.4
Net operating loss carryfowards originating in 2006	32.0
Net operating loss carryfowards originating in 2007	0.8
Net operating loss carryfowards originating in 2008	1.4
Net operating loss carryfowards originating in 2009	21.9
Net operating loss carryfowards originating in 2010	2.5
Net operating loss carryfowards originating in 2011	65.3
Net operating loss carryforwards originating in 2012	0.2
Net operating loss carryforwards originating in 2013	0.8
Net operating loss carryforwards originating in 2014	52.0
Net operating loss carryforwards originating in 2015	59.2
Net Operating Loss Carryforwards Originating in 2016	$ 0.6
Internal Revenue Service (IRS) [Member] \| Minimum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2023
Internal Revenue Service (IRS) [Member] \| Maximum [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2036
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 91.0	74.2
Amount of Net Operating Losses related to business acquisition	42.1	$ 36.1
Operating Loss Carryforwards, Valuation Allowance	$ 16.8

Taxes Tax Credit Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
General Business Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 191.0	$ 183.5
Amount of tax credit acquired in business combination	$ 0.5	0.5
Tax Credit Carryforward, Description	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits
Tax Credit Carryforward, Valuation Allowance	$ 0.4	0.4
General Business Tax Credit Carryforward [Member] \| KCPL [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 184.6	177.4
Tax Credit Carryforward, Description	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits
General Business Tax Credit Carryforward [Member] \| Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2028
General Business Tax Credit Carryforward [Member] \| Minimum [Member] \| KCPL [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2028
General Business Tax Credit Carryforward [Member] \| Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2037
General Business Tax Credit Carryforward [Member] \| Maximum [Member] \| KCPL [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2037
Federal Alternative Minimum Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 87.6	$ 87.6
Tax Credit Carryforward, Description	These credits do not expire and can be used to reduce taxes paid in the future or become refundable starting in 2018.
Tax Credit Carryforward, Valuation Allowance	$ 5.8
State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 1.2
Tax Credit Carryforward, Description	The state income tax credits relate primarily to the Company's Kansas research and development tax credits, which do not expire.
State and Local Jurisdiction [Member] \| KCPL [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 1.2
Tax Credit Carryforward, Description	The state income tax credits relate primarily to the Company's Kansas research and development tax credits, which do not expire.

Taxes Valuation Allowance (Details) $ in Millions	12 Months Ended
Taxes Valuation Allowance (Details) $ in Millions	Dec. 31, 2017 USD ($)
Valuation Allowance [Line Items]
Valuation Allowance, Deferred Tax Asset, Change in Amount	$ 6.6
Valuation Allowance, Deferred Tax Asset, Explanation of Change	tax expense was recorded in continuing operations primarily related to a reduction in the refundable portion of federal Alternative Minimum Tax (AMT) credits.

Taxes Tax Reform (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
Taxes Tax Reform (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2017
Decrease in net deferred income tax liabilities for revaluation of deferred income tax assets and liabilities in rate base	$ 645.5
Decrease in net deferred income tax liabilities for tax gross-up adjustment for ratemaking purposes due to tax reform	222.8
Decrease In Net Deferred Income Tax Liabilities Due to Tax Reform	814.5
Income Tax Expense From Tax Reform Related to Deferred Taxes Not Included In Rate Base	11.1
Income Tax Expense From Tax Reform, Total	130.3	$ 130.3
Income Tax Expense From Tax Reform Related To Revaluation Of Non Reg Deferred Tax Assets	110.1
Income Tax Expense From Tax Reform Related To The Reassessment Of The Valuation Allowance For Refundable AMT Credits And State NOLs	9.1
Income Tax Savings From Tax Reform			$ 100.0
Federal Statutory Income Tax Rate, Current			35.00%
Federal Statutory Income Tax Rate, New			21.00%
KCPL [Member]
Decrease in net deferred income tax liabilities for revaluation of deferred income tax assets and liabilities in rate base	471.8
Decrease in net deferred income tax liabilities for tax gross-up adjustment for ratemaking purposes due to tax reform	163.6
Decrease In Net Deferred Income Tax Liabilities Due to Tax Reform	682.8
Income Tax Expense From Tax Reform Related to Deferred Taxes Not Included In Rate Base	$ 16.5

Segments and Related Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 597.7	$ 857.2	$ 682.6	$ 570.7	$ 576.3	$ 856.8	$ 670.8	$ 572.1	$ 2,708.2	$ 2,676.0	$ 2,502.2
Depreciation and amortization									(371.1)	(344.8)	(330.4)
Interest charges									(290.7)	(161.5)	(199.3)
Income tax expense									(233.3)	(172.2)	(122.7)
Net income (loss)									(106.2)	290.0	213.0
Assets	12,457.9				13,570.0				12,457.9	13,570.0	10,738.6
Capital expenditures									573.5	609.4	677.1
Operating Segments [Member] \| Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,708.2	2,676.0	2,502.2
Depreciation and amortization									(371.1)	(344.8)	(330.4)
Interest charges									(196.9)	(196.1)	(190.9)
Income tax expense									(169.4)	(164.3)	(120.8)
Net income (loss)									256.9	292.1	223.8
Assets	11,508.1				11,444.2				11,508.1	11,444.2	11,045.5
Capital expenditures									573.5	609.4	677.1
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues									0.0	0.0	0.0
Depreciation and amortization									0.0	0.0	0.0
Interest charges									(125.9)	2.5	(40.5)
Income tax expense									(63.9)	(7.9)	(1.9)
Net income (loss)									(363.1)	(2.1)	(10.8)
Assets	1,285.7				2,461.3				1,285.7	2,461.3	(51.1)
Capital expenditures									0.0	0.0	0.0
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues									0.0	0.0	0.0
Depreciation and amortization									0.0	0.0	0.0
Interest charges									32.1	32.1	32.1
Income tax expense									0.0	0.0	0.0
Net income (loss)									0.0	0.0	0.0
Assets	$ (335.9)				$ (335.5)				(335.9)	(335.5)	(255.8)
Capital expenditures									$ 0.0	$ 0.0	$ 0.0

Jointly Owned Electric Utility Plants (Details) $ in Millions	Dec. 31, 2017 USD ($) MW	Dec. 31, 2016 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Nuclear fuel, net	$ 72.4	$ 62.0
Jeffrey Energy Center [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	8.00%
Utility plant in service	$ 201.1
Accumulated depreciation	82.0
Nuclear fuel, net	0.0
Construction work in progress	$ 2.5
Accredited capacity \| MW	173
Iatan Common [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	79.00%
Utility plant in service	$ 491.1
Accumulated depreciation	130.7
Nuclear fuel, net	0.0
Construction work in progress	$ 21.7
Iatan No. 2 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	73.00%
Utility plant in service	$ 1,355.8
Accumulated depreciation	413.0
Nuclear fuel, net	0.0
Construction work in progress	$ 35.0
Accredited capacity \| MW	641
Iatan No. 1 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	88.00%
Utility plant in service	$ 699.9
Accumulated depreciation	280.8
Nuclear fuel, net	0.0
Construction work in progress	$ 31.8
Accredited capacity \| MW	616
LaCygne Station [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%
Utility plant in service	$ 1,191.1
Accumulated depreciation	347.8
Nuclear fuel, net	0.0
Construction work in progress	$ 8.6
Accredited capacity \| MW	699
Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	47.00%
Utility plant in service	$ 1,854.2
Accumulated depreciation	918.1
Nuclear fuel, net	72.4
Construction work in progress	$ 91.8
Accredited capacity \| MW	552
KCPL [Member] \| Iatan Common [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	61.00%
Utility plant in service	$ 401.8
Accumulated depreciation	117.5
Nuclear fuel, net	0.0
Construction work in progress	$ 12.0
KCPL [Member] \| Iatan No. 2 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	55.00%
Utility plant in service	$ 1,041.6
Accumulated depreciation	366.6
Nuclear fuel, net	0.0
Construction work in progress	$ 14.8
Accredited capacity \| MW	482
KCPL [Member] \| Iatan No. 1 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	70.00%
Utility plant in service	$ 561.7
Accumulated depreciation	228.9
Nuclear fuel, net	0.0
Construction work in progress	$ 7.6
Accredited capacity \| MW	490
KCPL [Member] \| LaCygne Station [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%
Utility plant in service	$ 1,191.1
Accumulated depreciation	347.8
Nuclear fuel, net	0.0
Construction work in progress	$ 8.6
Accredited capacity \| MW	699
KCPL [Member] \| Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	47.00%
Utility plant in service	$ 1,854.2
Accumulated depreciation	918.1
Nuclear fuel, net	72.4
Construction work in progress	$ 91.8
Accredited capacity \| MW	552

Quarterly Operating Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating revenues		$ 597.7	$ 857.2	$ 682.6	$ 570.7	$ 576.3	$ 856.8	$ 670.8	$ 572.1	$ 2,708.2	$ 2,676.0	$ 2,502.2
Operating income		73.8	305.9	176.5	47.4	64.8	281.9	182.3	89.9	$ 603.6	$ 618.9	$ 530.1
Net income (loss)		$ (100.1)	$ 10.5	$ (7.0)	$ (9.6)	$ 98.0	$ 133.6	$ 32.0	$ 26.4
Basic and diluted earnings (loss) per common share		$ (0.46)	$ 0.02	$ (0.10)	$ (0.11)	$ 0.39	$ 0.86	$ 0.20	$ 0.17	$ (0.67)	$ 1.61	$ 1.37
Income Tax Expense From Tax Reform, Total	$ 130.3	$ 130.3
KCPL [Member]
Operating revenues		416.4	$ 595.7	$ 482.7	$ 395.9	$ 401.3	$ 597.6	$ 475.6	$ 400.9	$ 1,890.7	$ 1,875.4	$ 1,713.8
Operating income		61.8	209.9	113.8	58.2	54.4	219.2	137.9	70.6	$ 443.7	$ 482.1	$ 364.0
Net income (loss)		$ 1.9	$ 114.1	$ 49.6	$ 14.2	$ 16.8	$ 117.7	$ 65.9	$ 24.6

Schedule I Financial Statements of Parent Company Statements of Income & OCI (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Expenses
Costs to achieve the anticipated merger with Westar Energy, Inc.									$ 31.8	$ 34.2	$ 0.0
General taxes									229.2	226.7	213.2
Operating income	$ 73.8	$ 305.9	$ 176.5	$ 47.4	$ 64.8	$ 281.9	$ 182.3	$ 89.9	603.6	618.9	530.1
Other Income (Expense)
Equity in earnings (loss) from subsidiaries									2.5	2.0	1.2
Non-operating income									50.7	17.1	11.7
Loss on extinguishment of debt									(82.8)	0.0	0.0
Loss on Series B Preferred Stock dividend make-whole provisions									(124.8)	0.0	0.0
Total									(188.3)	2.8	3.7
Interest (charges) income									(290.7)	(161.5)	(199.3)
Income (loss) before income tax (expense) benefit and income from equity investments									124.6	460.2	334.5
Income tax expense									(233.3)	(172.2)	(122.7)
Net income (loss)	$ (100.1)	$ 10.5	$ (7.0)	$ (9.6)	$ 98.0	$ 133.6	$ 32.0	$ 26.4
Preferred stock dividend requirements and redemption premium									37.3	16.5	1.6
Earnings available for common shareholders									$ (143.5)	$ 273.5	$ 211.4
Average number of basic common shares outstanding									215.5	169.4	154.2
Average number of diluted common shares outstanding									215.5	169.8	154.8
Basic and diluted earnings (loss) per common share	$ (0.46)	$ 0.02	$ (0.10)	$ (0.11)	$ 0.39	$ 0.86	$ 0.20	$ 0.17	$ (0.67)	$ 1.61	$ 1.37
Common Stock, Dividends, Per Share, Declared									$ 1.100	$ 1.0625	$ 0.9975
Comprehensive Income
Net income (loss)	$ (100.1)	$ 10.5	$ (7.0)	$ (9.6)	$ 98.0	$ 133.6	$ 32.0	$ 26.4
Other comprehensive income
Reclassification to expenses, net of tax									$ 4.9	$ 5.6	$ 5.7
Derivative hedging activity, net of tax									4.9	5.6	5.7
Total other comprehensive income									4.4	5.4	6.7
Comprehensive income									(101.8)	295.4	219.7
Great Plains Energy [Member]
Operating Expenses
General and administrative									2.3	2.7	0.9
Costs to achieve the anticipated merger with Westar Energy, Inc.									16.1	18.3	0.0
General taxes									0.1	0.1	0.2
Total									18.5	21.1	1.1
Operating income									(18.5)	(21.1)	(1.1)
Other Income (Expense)
Equity in earnings (loss) from subsidiaries									141.4	287.5	220.9
Non-operating income									51.5	31.3	29.7
Loss on extinguishment of debt									(82.8)	0.0	0.0
Loss on Series B Preferred Stock dividend make-whole provisions									(124.8)	0.0	0.0
Total									(14.7)	318.8	250.6
Interest (charges) income									(125.6)		(40.3)
Interest (charges) income										2.6
Income (loss) before income tax (expense) benefit and income from equity investments									(158.8)	300.3	209.2
Income tax expense									52.6	(10.3)	3.8
Net income (loss)									(106.2)	290.0	213.0
Preferred stock dividend requirements and redemption premium									37.3	16.5	1.6
Earnings available for common shareholders									$ (143.5)	$ 273.5	$ 211.4
Average number of basic common shares outstanding									215.5	169.4	154.2
Average number of diluted common shares outstanding									215.5	169.8	154.8
Basic and diluted earnings (loss) per common share									$ (0.67)	$ 1.61	$ 1.37
Comprehensive Income
Net income (loss)									$ (106.2)	$ 290.0	$ 213.0
Other comprehensive income
Reclassification to expenses									0.4	0.4	0.5
Income tax (expense) benefit on reclassification to expenses									(0.1)	(0.2)	(0.1)
Reclassification to expenses, net of tax									0.3	0.2	0.4
Derivative hedging activity, net of tax									0.3	0.2	0.4
Other comprehensive income from subsidiaries, net of tax									4.1	5.2	6.3
Total other comprehensive income									4.4	5.4	6.7
Comprehensive income									$ (101.8)	$ 295.4	$ 219.7

Schedule I Financial Statements of Parent Company Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current Assets
Cash and cash equivalents	$ 1,125.4	$ 1,293.1	$ 11.3	$ 13.0
Time deposit	0.0	1,000.0
Interest rate derivative instruments	91.4	79.3
Total	1,863.1	3,059.5
Investments and Other Assets
Other	128.8	113.9
Assets	12,457.9	13,570.0	10,738.6
Current Liabilities
Notes payable	11.0	0.0
Current maturities of long-term debt	351.1	382.1
Accrued taxes	35.1	33.3
Accrued interest	42.8	50.8
Other	59.2	32.6
Total	1,448.8	1,384.8
Deferred Credits and Other Liabilities
Deferred Credits and Other Liabilities	2,731.7	2,658.0
Capitalization
Common stock	4,233.1	4,217.0
Preference Stock	0.0	836.2
Retained earnings	737.9	1,119.2
Treasury stock - 137,589 and 128,087 shares, at cost	(4.0)	(3.8)
Accumulated other comprehensive loss	(2.2)	(6.6)	(12.0)
Total shareholders' equity	4,964.8	6,162.0	3,695.5
Long-term debt (Note 12)	3,312.6	3,365.2
Total	8,277.4	9,527.2
Commitments and Contingencies
Total	12,457.9	13,570.0
Great Plains Energy [Member]
Current Assets
Cash and cash equivalents	1,114.2	1,283.9	$ 0.0	$ 0.0
Time deposit	0.0	1,000.0
Accounts receivable from subsidiaries	34.8	10.6
Notes receivable from subsidiaries, current	2.0	2.0
Interest rate derivative instruments	91.4	79.3
Other current assets	2.3	26.1
Total	1,244.7	2,401.9
Investments and Other Assets
Investment in KCP&L	2,513.2	2,541.5
Investment in other subsidiaries	1,240.1	1,341.6
Notes receivable from subsidiaries, noncurrent	634.9	634.9
Deferred income taxes	11.6	12.8
Other	1.0	16.3
Total investments and other assets	4,400.8	4,547.1
Assets	5,645.5	6,949.0
Current Liabilities
Notes payable	11.0	0.0
Current maturities of long-term debt	0.0	100.0
Accounts payable to subsidiaries	21.7	10.8
Accrued taxes	0.0	12.9
Accrued interest	2.1	10.1
Other	5.9	12.8
Total	40.7	146.6
Deferred Credits and Other Liabilities
Deferred Credits and Other Liabilities	1.8	2.2
Capitalization
Common stock	4,233.1	4,217.0
Preference Stock	0.0	836.2
Retained earnings	737.9	1,119.2
Treasury stock - 137,589 and 128,087 shares, at cost	(4.0)	(3.8)
Accumulated other comprehensive loss	(2.2)	(6.6)
Total shareholders' equity	4,964.8	6,162.0
Long-term debt (Note 12)	638.2	638.2
Total	5,603.0	6,800.2
Commitments and Contingencies
Total	$ 5,645.5	$ 6,949.0

Schedule I Financial Statements of Parent Company Balance Sheet Parenthetical (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Common Stock, Shares Authorized	600,000,000	600,000,000	600,000,000
Common Stock, Shares, Issued	215,801,723	215,479,105
Treasury Stock, Shares	137,589	128,087
Great Plains Energy [Member]
Common Stock, Shares Authorized	600,000,000	600,000,000
Common Stock, Shares, Issued	215,801,723	215,479,105
Treasury Stock, Shares	137,589	128,087
Preferred Stock, Shares Authorized	11,000,000	11,000,000
Preferred Stock, Dividend Rate, Percentage	7.00%	7.00%
Preferred Stock, Shares Issued	0	862,500
Preferred Stock, Liquidation Preference, Value	$ 1,000	$ 1,000
Series B Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage	7.00%	7.00%
Preferred Stock, Shares Issued	0	862,500

Schedule I Financial Statements of Parent Company Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities
Net income (loss)	$ (100.1)	$ 10.5	$ (7.0)	$ (9.6)	$ 98.0	$ 133.6	$ 32.0	$ 26.4
Adjustments to reconcile income to net cash from operating activities:
Deferred income taxes, net									$ 235.4	$ 170.1	$ 124.9
Equity in earnings from subsidiaries									(2.5)	(2.0)	(1.2)
Fair value impacts of interest rate swaps									(12.1)	(79.3)	0.0
Loss on Series B Preferred Stock dividend make-whole provisions									124.8	0.0	0.0
Loss on extinguishment of debt									82.8	0.0	0.0
Cash flows affected by changes in:
Accrued taxes									1.5	8.1	1.1
Accrued interest									(8.0)	6.1	3.4
Other									20.6	28.1	(7.8)
Net cash from operating activities									810.5	784.0	753.1
Cash Flows from Investing Activities
Purchase of time deposit									0.0	(1,000.0)	0.0
Proceeds from time deposit									1,000.0	0.0	0.0
Other investing activities									(45.6)	(64.0)	(48.2)
Net cash from investing activities									370.2	(1,683.5)	(734.4)
Cash Flows from Financing Activities
Issuance of common stock									2.9	1,603.7	3.0
Issuance of preferred stock									0.0	862.5	0.0
Issuance of long-term debt									4,591.1	0.0	348.8
Issuance fees									(38.3)	(143.6)	(3.0)
Repayment of long-term debt, including redemption premium									(4,725.1)	(1.1)	(87.0)
Net change in short-term borrowings									53.0	100.8	(128.3)
Dividends paid									(272.0)	(194.0)	(155.5)
Other financing activities									(4.2)	(4.3)	(2.4)
Net cash from financing activities									(1,348.4)	2,181.3	(20.4)
Net Change in Cash and Cash Equivalents									(167.7)	1,281.8	(1.7)
Cash and Cash Equivalents at Beginning of Year				1,293.1				11.3	1,293.1	11.3	13.0
Cash and Cash Equivalents at End of Year	1,125.4				1,293.1				1,125.4	1,293.1	11.3
Great Plains Energy [Member]
Cash Flows from Operating Activities
Net income (loss)									(106.2)	290.0	213.0
Adjustments to reconcile income to net cash from operating activities:
Amortization									26.2	30.4	0.8
Deferred income taxes, net									2.3	21.8	(1.7)
Equity in earnings from subsidiaries									(141.4)	(287.5)	(220.9)
Fair value impacts of interest rate swaps									(12.1)	(79.3)	0.0
Loss on Series B Preferred Stock dividend make-whole provisions									124.8	0.0	0.0
Loss on extinguishment of debt									82.8	0.0	0.0
Cash flows affected by changes in:
Accounts receivable from subsidiaries									(21.6)	(9.8)	(0.1)
Accounts payable to subsidiaries									10.9	(20.9)	1.3
Other accounts payable									(2.2)	7.0	0.0
Accrued taxes									(12.9)	8.4	0.3
Accrued interest									(8.0)	6.0	0.0
Cash dividends from subsidiaries									275.0	239.0	157.0
Other									22.3	8.0	8.7
Net cash from operating activities									239.9	213.1	158.4
Cash Flows from Investing Activities
Purchase of time deposit									0.0	(1,000.0)	0.0
Proceeds from time deposit									1,000.0	0.0	0.0
Intercompany lending									0.0	0.0	(1.4)
Net money pool lending									0.0	3.7	(0.4)
Investment in subsidiary									(0.6)	(7.3)	(7.8)
Net cash from investing activities									999.4	(1,003.6)	(9.6)
Cash Flows from Financing Activities
Issuance of common stock									2.9	1,603.7	3.0
Issuance of preferred stock									0.0	862.5	0.0
Issuance of long-term debt									4,291.9	0.0	0.0
Issuance fees									(32.2)	(143.4)	0.0
Repayment of long-term debt, including redemption premium									(4,443.0)	0.0	0.0
Net change in short-term borrowings									11.0	(10.0)	6.0
Dividends paid									(272.0)	(194.0)	(155.5)
Redemption of preferred stock									(963.4)	(40.1)	0.0
Other financing activities									(4.2)	(4.3)	(2.3)
Net cash from financing activities									(1,409.0)	2,074.4	(148.8)
Net Change in Cash and Cash Equivalents									(169.7)	1,283.9	0.0
Cash and Cash Equivalents at Beginning of Year				$ 1,283.9				$ 0.0	1,283.9	0.0	0.0
Cash and Cash Equivalents at End of Year	$ 1,114.2				$ 1,283.9				$ 1,114.2	$ 1,283.9	$ 0.0

Schedule II Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 4.0	$ 3.8	$ 2.8
Additions charged to costs and expenses	10.5	9.0	10.5
Additions charged to other accounts	8.1	8.1	8.7
Deductions	17.9	16.9	18.2
Balance at end of period	4.7	4.0	3.8
Allowance for Doubtful Accounts [Member] \| KCPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	1.8	1.8	1.2
Additions charged to costs and expenses	7.5	6.4	7.1
Additions charged to other accounts	5.6	5.5	5.8
Deductions	12.7	11.9	12.3
Balance at end of period	2.2	1.8	1.8
Legal Reserve [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	16.1	5.9	4.7
Additions charged to costs and expenses	0.8	10.4	2.6
Additions charged to other accounts	0.0	0.0	0.0
Deductions	9.2	0.2	1.4
Balance at end of period	7.7	16.1	5.9
Legal Reserve [Member] \| KCPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	15.1	5.3	2.9
Additions charged to costs and expenses	0.0	9.8	2.6
Additions charged to other accounts	0.0	0.0	0.0
Deductions	9.0	0.0	0.2
Balance at end of period	6.1	15.1	5.3
Reserve for Environmental Costs [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	1.7	1.7	1.7
Additions charged to costs and expenses	0.1	0.0	0.0
Additions charged to other accounts	0.0	0.0	0.0
Deductions	0.0	0.0	0.0
Balance at end of period	1.8	1.7	1.7
Reserve for Environmental Costs [Member] \| KCPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	0.3	0.3	0.3
Additions charged to costs and expenses	0.0	0.0	0.0
Additions charged to other accounts	0.0	0.0	0.0
Deductions	0.0	0.0	0.0
Balance at end of period	0.3	0.3	0.3
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	16.4	19.9	16.6
Additions charged to costs and expenses	11.3	0.1	4.9
Additions charged to other accounts	0.0	0.0	0.0
Deductions	4.7	3.6	1.6
Balance at end of period	23.0	16.4	19.9
Valuation Allowance of Deferred Tax Assets [Member] \| KCPL [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	0.0	0.7	0.0
Additions charged to costs and expenses	1.2	0.0	0.7
Additions charged to other accounts	0.0	0.0	0.0
Deductions	1.2	0.7	0.0
Balance at end of period	$ 0.0	$ 0.0	$ 0.7

Regulatory Matters Asset (Details) - USD ($) $ in Millions	12 Months Ended
Regulatory Matters Asset (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 913.9	$ 1,048.0
Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0.0	148.7
Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	9.9	11.7
Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	30.3	28.6
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	118.5	94.5
Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	487.9	472.6
Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	60.3	73.3
Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	73.7	69.9
Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	17.6	18.6
Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	38.7	43.0
Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	6.6	3.6
Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	59.6	70.8
Transmission Delivery Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	3.2	3.1
LaCygne Deferred Depreciation [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	2.7	2.8
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	4.9	6.8
KCPL Greater Missouri Operations [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	222.0	246.2
KCPL Greater Missouri Operations [Member] \| Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0.0	24.8
KCPL Greater Missouri Operations [Member] \| Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	1.2	1.7
KCPL Greater Missouri Operations [Member] \| Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0.0	0.0
KCPL Greater Missouri Operations [Member] \| Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	24.2	24.9
KCPL Greater Missouri Operations [Member] \| Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	108.2	104.7
Amount not included in rate base	61.4
KCPL Greater Missouri Operations [Member] \| Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	19.4	27.4
Amount not included in rate base	10.9
KCPL Greater Missouri Operations [Member] \| Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	12.0	0.0
KCPL Greater Missouri Operations [Member] \| Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 4.7	5.0
Regulatory Noncurrent Asset, End Date for Recovery	Dec. 31, 2038
KCPL Greater Missouri Operations [Member] \| Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 13.7	16.1
Regulatory Noncurrent Asset, End Date for Recovery	Dec. 31, 2059
KCPL Greater Missouri Operations [Member] \| Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 0.0	0.0
KCPL Greater Missouri Operations [Member] \| Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	37.0	41.6
KCPL Greater Missouri Operations [Member] \| Transmission Delivery Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0.0	0.0
KCPL Greater Missouri Operations [Member] \| LaCygne Deferred Depreciation [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0.0	0.0
KCPL Greater Missouri Operations [Member] \| Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	1.6	0.0
KCPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	691.9	801.8
KCPL [Member] \| Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0.0	123.9
KCPL [Member] \| Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	8.7	10.0
KCPL [Member] \| Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	30.3	28.6
KCPL [Member] \| Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	94.3	69.6
KCPL [Member] \| Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	379.7	367.9
Amount not included in rate base	366.3
KCPL [Member] \| Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	40.9	45.9
Amount not included in rate base	16.1
KCPL [Member] \| Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	61.7	69.9
KCPL [Member] \| Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	12.9	13.6
KCPL [Member] \| Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 25.0	26.9
Regulatory Noncurrent Asset, End Date for Recovery	Dec. 31, 2059
KCPL [Member] \| Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 6.6	3.6
KCPL [Member] \| Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 22.6	29.2
Regulatory Noncurrent Asset, End Date for Recovery	Dec. 31, 2020
KCPL [Member] \| Transmission Delivery Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 3.2	3.1
KCPL [Member] \| LaCygne Deferred Depreciation [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 2.7	2.8
Regulatory Noncurrent Asset, End Date for Recovery	Dec. 31, 2040
KCPL [Member] \| Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 3.3	$ 6.8

Goodwill (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill	$ 169.0	$ 169.0

Summary of Significant Accounting Policies Summary of Significant Accounting Policies New Accounting Pronouncements (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
KCPL [Member] \| Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU 2016-09 (Note 1)	$ 0.7	$ 0.0	$ 0.0

Legal Proceedings Loss Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2016	Dec. 31, 2016
MPS Merchant Services, Inc. [Member] \| GMO Western Energy Crisis [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount Awarded to Other Party	$ 7.5	$ 7.5

Fair Value Measurements (Details) $ in Millions	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	$ 91.4		$ 79.3
Fair Value Inputs, Contingency Factor, Interest Rate Derivative	0.35		0.35
Interest Rate Contract [Member] \| Great Plains Energy [Member]
Assets [Abstract]
Derivatives, Interest Rate Swaps, Finalized Settlement Value		$ 140.6
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Derivative instruments, assets	$ 91.4		$ 79.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	258.4		222.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	10.9		11.3
Total assets	360.7		313.5
Fair Value, Measurements, Recurring [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	258.4		222.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	10.9		11.3
Total assets	269.3		234.2
Fair Value, Measurements, Recurring [Member] \| Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	91.4		79.3
Fair Value, Measurements, Recurring [Member] \| Interest Rate Contract [Member] \| Other Consolidated Entities [Member]
Assets [Abstract]
Derivative instruments, assets	91.4		$ 79.3
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6
Fair Value Inputs, Contingency Factor, Interest Rate Derivative	0.35		0.35
Fair Value, Measurements, Recurring [Member] \| Equity Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	$ 183.8		$ 153.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.5		0.9
Fair Value, Measurements, Recurring [Member] \| Debt Securities [Member] \| KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.7		4.8
Fair Value, Measurements, Recurring [Member] \| US Treasury and Government [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	35.3		27.8
Fair Value, Measurements, Recurring [Member] \| US Government Corporations and Agencies Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.4		1.7
Fair Value, Measurements, Recurring [Member] \| US States and Political Subdivisions Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.1		3.2
Fair Value, Measurements, Recurring [Member] \| Corporate Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	34.1		32.4
Fair Value, Measurements, Recurring [Member] \| Foreign Government Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1		0.1
Fair Value, Measurements, Recurring [Member] \| Cash Equivalents [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.5		3.8
Fair Value, Measurements, Recurring [Member] \| Cash and Cash Equivalents [Member] \| KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	7.7		5.6
Fair Value, Measurements, Recurring [Member] \| Other Trust Assets [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0.0		0.0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	221.7		185.5
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.5		6.6
Total assets	230.2		192.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	221.7		185.5
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.5		6.6
Total assets	230.2		192.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Interest Rate Contract [Member] \| Other Consolidated Entities [Member]
Assets [Abstract]
Derivative instruments, assets	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Equity Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	183.8		153.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.5		0.9
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Debt Securities [Member] \| KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.3		0.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US Treasury and Government [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	35.3		27.8
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US Government Corporations and Agencies Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US States and Political Subdivisions Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Foreign Government Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Cash Equivalents [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.5		3.8
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Cash and Cash Equivalents [Member] \| KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	7.7		5.6
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Other Trust Assets [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	0.0		0.0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	36.7		37.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.4		4.7
Total assets	39.1		42.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	36.7		37.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.4		4.7
Total assets	39.1		42.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Contract [Member] \| Other Consolidated Entities [Member]
Assets [Abstract]
Derivative instruments, assets	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Equity Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Debt Securities [Member] \| KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.4		4.7
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US Treasury and Government [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US Government Corporations and Agencies Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.4		1.7
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US States and Political Subdivisions Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	2.1		3.2
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	34.1		32.4
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign Government Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1		0.1
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Cash Equivalents [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Cash and Cash Equivalents [Member] \| KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Other Trust Assets [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	91.4		79.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Total assets	91.4		79.3
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Total assets	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	91.4		79.3
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Contract [Member] \| Other Consolidated Entities [Member]
Assets [Abstract]
Derivative instruments, assets	91.4		79.3
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Equity Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Debt Securities [Member] \| KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| US Treasury and Government [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| US Government Corporations and Agencies Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| US States and Political Subdivisions Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Corporate Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Foreign Government Debt Securities [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Cash Equivalents [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0		0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Cash and Cash Equivalents [Member] \| KCPL [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0		$ 0.0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Other Trust Assets [Member] \| KCPL [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	$ 0.0