Evergy Metro 10-K 23 Feb 17 2016 Q4 Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Feb. 21, 2017	Jun. 30, 2016
Document Information [Line Items]
Entity Registrant Name	Great Plains Energy Inc
Entity Central Index Key	1,143,068
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			$ 4,700,571,576
Entity Common Stock, Shares Outstanding		215,384,601
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q4
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Revenues
Electric revenues	$ 2,676	$ 2,502.2	$ 2,568.2
Operating Expenses
Fuel and purchased power	590.1	608.7	742.5
Transmission	84.8	89.1	74.7
Utility operating and maintenance expenses	759.5	724.8	701.9
Costs to achieve the anticipated acquisition of Westar Energy, Inc.	34.2	0	0
Depreciation and amortization	344.8	330.4	306
General taxes	226.7	213.2	204.6
Other	17	5.9	4
Total	2,057.1	1,972.1	2,033.7
Operating income	618.9	530.1	534.5
Non-operating income	17.1	11.7	25
Non-operating expenses	(14.3)	(8)	(12.5)
Interest charges	(161.5)	(199.3)	(188.5)
Income before income tax expense and income from equity investments	460.2	334.5	358.5
Income tax expense	(172.2)	(122.7)	(115.7)
Income from equity investments, net of income taxes	2	1.2	0
Net income	290	213	242.8
Preferred stock dividend requirements and redemption premium	16.5	1.6	1.6
Earnings available for common shareholders	$ 273.5	$ 211.4	$ 241.2
Average number of basic common shares outstanding	169.4	154.2	153.9
Average number of diluted common shares outstanding	169.8	154.8	154.1
Basic and diluted earnings per common share	$ 1.61	$ 1.37	$ 1.57
Comprehensive Income
Net income	$ 290	$ 213	$ 242.8
Other comprehensive income
Reclassification to expenses, net of tax	5.6	5.7	8
Derivative hedging activity, net of tax	5.6	5.7	8
Net gain (loss) arising during period	(1.1)	1	(3)
Income tax (expense) benefit	0.4	(0.4)	1.2
Net gain (loss) arising during period, net of tax	(0.7)	0.6	(1.8)
Amortization of net losses included in net periodic benefit costs, net of tax	0.5	0.4	0.4
Change in unrecognized pension expense, net of tax	(0.2)	1	(1.4)
Total other comprehensive income	5.4	6.7	6.6
Comprehensive income	295.4	219.7	249.4
Kansas City Power and Light Company [Member]
Operating Revenues
Electric revenues	1,875.4	1,713.8	1,730.8
Operating Expenses
Fuel and purchased power	372.7	397.1	472.7
Transmission	56.4	58.4	47.2
Utility operating and maintenance expenses	525.8	494.2	489.1
Costs to achieve the anticipated acquisition of Westar Energy, Inc.	10.9	0	0
Depreciation and amortization	247.5	235.7	213.9
General taxes	177.5	163.5	159.1
Other	2.5	0.9	(1.3)
Total	1,393.3	1,349.8	1,380.7
Operating income	482.1	364	350.1
Non-operating income	11.8	8.4	20.4
Non-operating expenses	(7.6)	(7.2)	(8.3)
Interest charges	(139.4)	(135.6)	(124.1)
Income before income tax expense and income from equity investments	346.9	229.6	238.1
Income tax expense	(121.9)	(76.8)	(75.7)
Net income	225	152.8	162.4
Comprehensive Income
Net income	225	152.8	162.4
Other comprehensive income
Reclassification to expenses, net of tax	5.4	5.3	5.3
Derivative hedging activity, net of tax	5.4	5.3	5.3
Total other comprehensive income	5.4	5.3	5.3
Comprehensive income	$ 230.4	$ 158.1	$ 167.7

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Current Assets
Cash and cash equivalents	$ 1,293.1	$ 11.3
Time deposit	1,000	0
Receivables, net	166	147.7
Accounts receivable pledged as collateral	172.4	175
Fuel inventories, at average cost	108.8	118.4
Materials and supplies, at average cost	162.2	155.7
Deferred refueling outage costs	22.3	19.2
Refundable income taxes	0	3.8
Derivative instruments	81.5	0.8
Prepaid expenses and other assets	53.2	32.3
Total	3,059.5	664.2
Utility Plant, at Original Cost
Electric	13,597.7	13,189.9
Less - accumulated depreciation	5,106.9	4,943.7
Net utility plant in service	8,490.8	8,246.2
Construction work in progress	403.9	347.9
Nuclear fuel, net of amortization of $172.1 and $192.5	62	68.3
Total	8,956.7	8,662.4
Investments and Other Assets
Nuclear decommissioning trust fund	222.9	200.7
Regulatory assets	1,048	979.1
Goodwill	169	169
Other	113.9	63.2
Total	1,553.8	1,412
Total	13,570	10,738.6
Current Liabilities
Notes payable	0	10
Collateralized note payable	172.4	175
Commercial paper	334.8	224
Current maturities of long-term debt	382.1	1.1
Accounts payable	323.7	352.9
Accrued taxes	33.3	31.6
Accrued interest	50.8	44.7
Accrued compensation and benefits	52.1	41.4
Pension and post-retirement liability	3	3.4
Other	32.6	31.6
Total	1,384.8	915.7
Deferred Credits and Other Liabilities
Deferred income taxes	1,329.7	1,158.8
Deferred tax credits	126.2	125.1
Asset retirement obligations	316	275.9
Pension and post-retirement liability	488.3	455.2
Regulatory liabilities	309.9	284.4
Other	87.9	82.9
Total	2,658	2,382.3
Shareholders' equity
Common stock	4,217	2,646.7
Retained earnings	1,119.2	1,024.4
Treasury stock - 128,087 and 101,229 shares, at cost	(3.8)	(2.6)
Accumulated other comprehensive loss	(6.6)	(12)
Total shareholders' equity	6,162	3,695.5
Long-term debt (Note 12)	3,365.2	3,745.1
Total	9,527.2	7,440.6
Commitments and Contingencies (Note 15)
Total	13,570	10,738.6
Cumulative Preferred Stock [Member]
Shareholders' equity
Preferred Stock, Value, Issued	0	39
Series B Preferred Stock [Member]
Shareholders' equity
Preferred Stock, Value, Issued	836.2	0
Kansas City Power and Light Company [Member]
Current Assets
Cash and cash equivalents	4.5	2.3
Receivables, net	139.1	129.2
Related party receivables	67.2	65.8
Accounts receivable pledged as collateral	110	110
Fuel inventories, at average cost	72.9	83.5
Materials and supplies, at average cost	118.9	114.6
Deferred refueling outage costs	22.3	19.2
Refundable income taxes	12.7	79
Prepaid expenses and other assets	27.9	27.6
Total	575.5	631.2
Utility Plant, at Original Cost
Electric	9,925.1	9,640.4
Less - accumulated depreciation	3,858.4	3,722.6
Net utility plant in service	6,066.7	5,917.8
Construction work in progress	300.4	246.6
Nuclear fuel, net of amortization of $172.1 and $192.5	62	68.3
Total	6,429.1	6,232.7
Investments and Other Assets
Nuclear decommissioning trust fund	222.9	200.7
Regulatory assets	801.8	732.4
Other	29.1	17.6
Total	1,053.8	950.7
Total	8,058.4	7,814.6
Current Liabilities
Collateralized note payable	110	110
Commercial paper	132.9	180.3
Current maturities of long-term debt	281	0
Accounts payable	231.6	258.8
Accrued taxes	27	25.6
Accrued interest	32.4	32.4
Accrued compensation and benefits	52.1	41.4
Pension and post-retirement liability	1.6	2
Other	11.4	12.6
Total	880	663.1
Deferred Credits and Other Liabilities
Deferred income taxes	1,228.3	1,132.6
Deferred tax credits	122.8	123.8
Asset retirement obligations	278	239.3
Pension and post-retirement liability	465.8	433.4
Regulatory liabilities	187.4	164.6
Other	70.6	61.6
Total	2,352.9	2,155.3
Shareholders' equity
Common stock	1,563.1	1,563.1
Retained earnings	982.6	879.6
Accumulated other comprehensive loss	(4.2)	(9.6)
Total shareholders' equity	2,541.5	2,433.1
Long-term debt (Note 12)	2,284	2,563.1
Total	4,825.5	4,996.2
Commitments and Contingencies (Note 15)
Total	$ 8,058.4	$ 7,814.6

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016	Aug. 31, 2016
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 172.1	$ 192.5
Shareholder's equity
Common stock - shares authorized (in shares)	600,000,000	250,000,000	600,000,000
Common stock-shares issued (in shares)	215,479,105	154,504,900
Treasury stock- shares (in shares)	128,087	101,229
Series B Preferred Stock [Member]
Shareholder's equity
Preferred Stock, Shares Issued	862,500	0
Preferred Stock, Dividend Rate, Percentage	7.00%	7.00%
Preferred Stock, Liquidation Preference Per Share	$ 1,000	$ 1,000
Cumulative Preferred Stock [Member]
Shareholder's equity
Preferred Stock, Shares Issued	0	390,000
Preference stock, Shares Authorized	390,000	390,000
Cumulative preferred stock par value (in dollars per share)	$ 100	$ 100		$ 100
No Par Preference Stock [Member]
Shareholder's equity
Preference stock, Shares Authorized	11,000,000	11,000,000
Kansas City Power and Light Company [Member]
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 172.1	$ 192.5
Shareholder's equity
Common stock - shares authorized (in shares)	1,000	1,000
Common stock-shares issued (in shares)	1	1

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Flows from Operating Activities
Net income	$ 290	$ 213	$ 242.8
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	344.8	330.4	306
Amortization of:
Nuclear fuel	26.6	26.8	26.1
Other	77.5	47.7	46.1
Deferred income taxes, net	170.1	124.9	125.8
Investment tax credit amortization	(1.4)	(1.4)	(1.4)
Income from equity investments, net of income taxes	(2)	(1.2)	0
Fair value impact of interest rate swaps	(79.3)	0	0
Other operating activities (Note 3)	(42.3)	12.9	(47.2)
Net cash from operating activities	784	753.1	698.2
Cash Flows from Investing Activities
Utility capital expenditures	(609.4)	(677.1)	(773.7)
Allowance for borrowed funds used during construction	(6.8)	(5.8)	(13)
Purchases of nuclear decommissioning trust investments	(31.9)	(50.9)	(27.5)
Proceeds from nuclear decommissioning trust investments	28.6	47.6	24.2
Purchase of time deposit	(1,000)	0	0
Proceeds from sale of transmission assets	0	0	37.7
Other investing activities	(64)	(48.2)	(27.5)
Net cash from investing activities	(1,683.5)	(734.4)	(779.8)
Cash Flows from Financing Activities
Issuance of common stock	1,603.7	3	4.8
Issuance of preference stock	862.5	0	0
Issuance of long-term debt	0	348.8	0
Proceeds from issuance of long-term debt from remarketing	0	146.5	0
Repayment of long-term debt from remarketing	0	(146.5)	0
Issuance fees	(143.6)	(3)	(0.9)
Repayment of long-term debt	(1.1)	(87)	(13.4)
Net change in short-term borrowings	100.8	(128.3)	245.1
Net change in collateralized short-term borrowings	(2.6)	4	(4)
Dividends paid	(194)	(155.5)	(145.6)
Redemption of cumulative preferred stock	(40.1)	0	0
Purchase of treasury stock	(5)	(1.6)	(2.5)
Other financing activities	0.7	(0.8)	0.5
Net cash from financing activities	2,181.3	(20.4)	84
Net Change in Cash and Cash Equivalents	1,281.8	(1.7)	2.4
Cash and Cash Equivalents at Beginning of Year	11.3	13	10.6
Cash and Cash Equivalents at End of Year	1,293.1	11.3	13
Kansas City Power and Light Company [Member]
Cash Flows from Operating Activities
Net income	225	152.8	162.4
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	247.5	235.7	213.9
Amortization of:
Nuclear fuel	26.6	26.8	26.1
Other	33.9	29.1	29.3
Deferred income taxes, net	93.4	99.4	88.4
Investment tax credit amortization	(1)	(1)	(1)
Other operating activities (Note 3)	(2.1)	(61.5)	(64.7)
Net cash from operating activities	623.3	481.3	454.4
Cash Flows from Investing Activities
Utility capital expenditures	(418.8)	(518.3)	(635.9)
Allowance for borrowed funds used during construction	(5.6)	(3.9)	(11.1)
Purchases of nuclear decommissioning trust investments	(31.9)	(50.9)	(27.5)
Proceeds from nuclear decommissioning trust investments	28.6	47.6	24.2
Net money pool lending	0	0	4.7
Other investing activities	(23.8)	(25.5)	(15.2)
Net cash from investing activities	(451.5)	(551)	(660.8)
Cash Flows from Financing Activities
Issuance of long-term debt	0	348.8	0
Proceeds from issuance of long-term debt from remarketing	0	146.5	0
Repayment of long-term debt from remarketing	0	(146.5)	0
Issuance fees	(0.2)	(3)	(0.4)
Repayment of long-term debt	0	(85.9)	0
Net change in short-term borrowings	(47.4)	(178)	265.1
Net money pool borrowings	0	(12.6)	12.4
Dividends paid	(122)	0	(72)
Net cash from financing activities	(169.6)	69.3	205.1
Net Change in Cash and Cash Equivalents	2.2	(0.4)	(1.3)
Cash and Cash Equivalents at Beginning of Year	2.3	2.7	4
Cash and Cash Equivalents at End of Year	$ 4.5	$ 2.3	$ 2.7

Consolidated Statements of Comm

Consolidated Statements of Common Shareholders' Equity - USD ($) $ in Millions	Total	Kansas City Power and Light Company [Member]	Common Stock [Member]	Common Stock [Member]Kansas City Power and Light Company [Member]	Preferred Stock [Member]Cumulative Preferred Stock [Member]	Preferred Stock [Member]Preference Stock [Member]	Retained Earnings [Member]	Retained Earnings [Member]Kansas City Power and Light Company [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]Kansas City Power and Light Company [Member]
Beginning balance at Dec. 31, 2013		$ 2,275	$ 2,631.1	$ 1,563.1	$ 39	$ 0	$ 871.4	$ 636.4	$ (2.8)	$ (25.3)	$ (20.2)
Beginning balance (in shares) at Dec. 31, 2013			153,995,621	1	390,000	0
Beginning balance, treasury stock (in shares) at Dec. 31, 2013									(129,290)
Issuance of stock			$ 6.7			$ 0
Issuance of stock (in shares)			258,416			0
Equity compensation expense, net of forfeitures			$ 0.5
Redemption of cumulative preferred stock					$ 0
Redemption of cumulative preferred stock (in shares)					0
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.1)
Forfeiture of restricted common stock			0
Compensation expense recognized			2
Other			1.1
Net income	$ 242.8	162.4					242.8	162.4
Redemption premium on cumulative preferred stock							0
Dividends:
Common stock ($1.0625, $0.9975 and $0.935 per share)							(144)	(72)
Preferred stock - at required rates							(1.6)
Performance shares							(0.8)
Treasury shares acquired									$ (2.2)
Treasury shares acquired (in shares)									(85,744)
Treasury shares reissued									$ 2.7
Treasury shares reissued (in shares)									123,753
Derivative hedging activity, net of tax	8	5.3								8	5.3
Change in unrecognized pension expense, net of tax	(1.4)									(1.4)
Ending balance at Dec. 31, 2014	3,625.1		$ 2,639.3	$ 1,563.1	$ 39	$ 0	967.8	726.8	$ (2.3)	(18.7)	(14.9)
Ending balance, treasury stock (in shares) at Dec. 31, 2014									(91,281)
Ending balance (in shares) at Dec. 31, 2014			154,254,037	1	390,000	0
Issuance of stock			$ 6.6			$ 0
Issuance of stock (in shares)			250,863			0
Equity compensation expense, net of forfeitures			$ 1.9
Redemption of cumulative preferred stock					$ 0
Redemption of cumulative preferred stock (in shares)					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)
Net income	213	152.8					213	152.8
Redemption premium on cumulative preferred stock							0
Dividends:
Common stock ($1.0625, $0.9975 and $0.935 per share)							(153.9)	0
Preferred stock - at required rates							(1.6)
Performance shares							(0.9)
Treasury shares acquired									$ (2)
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	5.3								5.7	5.3
Change in unrecognized pension expense, net of tax	1									1
Ending balance at Dec. 31, 2015	$ 3,695.5	2,433.1	$ 2,646.7	$ 1,563.1	$ 39	$ 0	1,024.4	879.6	$ (2.6)	(12)	(9.6)
Ending balance, treasury stock (in shares) at Dec. 31, 2015	(101,229)								(101,229)
Ending balance (in shares) at Dec. 31, 2015			154,504,900	1	390,000	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 cumulative preferred stock					$ (39)
Redemption of cumulative preferred stock (in shares)					(390,000)
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.8)
Forfeiture of restricted common stock			0
Compensation expense recognized			2.7
Other			0.8
Net income	$ 290	225					290	225
Redemption premium on cumulative preferred stock							(0.6)
Dividends:
Common stock ($1.0625, $0.9975 and $0.935 per share)							(181)	(122)
Preferred stock - at required rates							(13)
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	5.4								5.6	5.4
Change in unrecognized pension expense, net of tax	(0.2)									(0.2)
Ending balance at Dec. 31, 2016	$ 6,162	$ 2,541.5	$ 4,217	$ 1,563.1	$ 0	$ 836.2	$ 1,119.2	$ 982.6	$ (3.8)	$ (6.6)	$ (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	1	0	862,500

Consolidated Statements of Com7

Consolidated Statements of Common Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock Transactions, Parenthetical Disclosures [Abstract]
Common Stock, Dividends, Per Share, Declared	$ 1.0625	$ 0.9975	$ 0.935

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
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 and a time deposit to be used to fund a portion of the cash consideration for the anticipated acquisition of Westar Energy, Inc. (Westar). 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 electric utility. See Note 23 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 time deposit matures in the first quarter of 2017 and the proceeds from this investment are expected to be used to fund a portion of the cash consideration for the anticipated acquisition of Westar. 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. Derivative instruments - The fair value of commodity derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlation among fuel prices, net of estimated credit risk. The fair value of interest rate derivative instruments is determined by calculating the net present value of expected payments and receipts under interest rate swaps using observable market inputs including interest rates and LIBOR swap rates. Management also discounts the value by a contingency factor that it believes is representative of what a market participant would use in valuing these instruments in order to account for the contingent nature of the settlement of these instruments. 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 used 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. See Note 19 for additional information regarding derivative financial instruments and hedging activities. 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. 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 5.7% in 2016 , 3.0% in 2015 and 5.7% in 2014 . The rates used to compute gross AFUDC for GMO averaged 1.6% in 2016 , 4.2% in 2015 and 6.1% in 2014 . 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 2016 2015 Utility plant, at original cost (millions) Generation (20 - 60 years) $ 8,106.4 $ 7,923.8 Transmission (15 - 70 years) 886.3 848.8 Distribution (8 - 66 years) 3,629.1 3,498.6 General (5 - 50 years) 975.9 918.7 Total (a) $ 13,597.7 $ 13,189.9 (a) Includes $261.2 million and $214.0 million at December 31, 2016 and 2015 , respectively, of land and other assets that are not depreciated. KCP&L December 31 2016 2015 Utility plant, at original cost (millions) Generation (20 - 60 years) $ 6,350.7 $ 6,222.5 Transmission (15 - 70 years) 484.1 465.3 Distribution (8 - 55 years) 2,298.4 2,215.2 General (5 - 50 years) 791.9 737.4 Total (a) $ 9,925.1 $ 9,640.4 (a) Includes $178.0 million and $136.5 million at December 31, 2016 and 2015 , respectively, of land and other assets that are not depreciated. 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 $308.8 million , $299.4 million and $277.9 million for 2016 , 2015 and 2014 , respectively. KCP&L's depreciation expense was $215.4 million , $208.5 million and $189.7 million for 2016 , 2015 and 2014 , 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 $70.3 million , $62.0 million and $60.4 million in 2016 , 2015 and 2014 , 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. 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. 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. If the fair value of a reporting unit is less than its carrying value including goodwill, an impairment charge for goodwill must be recognized in the financial statements. To measure the amount of the impairment loss to recognize, the implied fair value of the reporting unit goodwill is compared with its carrying 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. Great Plains Energy and KCP&L have established a net regulatory asset for the additional future revenues to be collected from customers for deferred income taxes. 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. Basic and Diluted Earnings per Common Share Calculation To determine basic earnings per common share (EPS), preferred stock dividend requirements and redemption premium are deducted from net income before dividing by the average number of common shares outstanding. To determine diluted EPS, preferred stock dividend requirements 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. 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. 2016 2015 2014 (millions, except per share amounts) Income Net income $ 290.0 $ 213.0 $ 242.8 Less: preferred stock dividend requirements and redemption premium 16.5 1.6 1.6 Earnings available for common shareholders $ 273.5 $ 211.4 $ 241.2 Common Shares Outstanding Average number of common shares outstanding 169.4 154.2 153.9 Add: effect of dilutive securities 0.4 0.6 0.2 Diluted average number of common shares outstanding 169.8 154.8 154.1 Basic and Diluted EPS $ 1.61 $ 1.37 $ 1.57 Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table. 2016 2015 2014 Assumed conversion of Series B Preferred Stock 7,805,460 — — Performance shares — — 482,987 Restricted stock shares — 900 3,287 Dividends Declared In February 2017 , Great Plains Energy's Board of Directors (Board) declared a quarterly dividend of $0.275 per share on Great Plains Energy's common stock. The common dividend is payable March 20, 2017 , to shareholders of record as of February 27, 2017 . The Board also declared a regular quarterly dividend on Great Plains Energy's Series B Preferred Stock. The dividend will be payable March 15, 2017 , to shareholders of record as of March 1, 2017 . In February 2017, KCP&L's Board of Directors declared a cash dividend payable to Great Plains Energy of $57 million payable on March 17, 2017 . New Accounting Standards In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (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. The ASU will replace most existing revenue recognition guidance in GAAP when it becomes effective. 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 Companies plan to adopt ASU No. 2014-09 on January 1, 2018. The standard permits the use of either the retrospective or cumulative effect transition method. The Companies have completed a review of the majority of their revenue arrangements and do not expect the standard to have a material impact on their consolidated financial statements. However, the Companies are still evaluating the impacts on revenue recognition of their remaining revenue arrangements and contracts where collectability is uncertain, as well as the accounting for contributions in aid of construction. The Companies are in the process of determining their method of adoption, which depends in part on completing the evaluation of the remaining items noted above. 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 . The Companies are evaluating the effect that ASU No. 2016-02 will have on their consolidated financial statements and related disclosures and have not yet determined the effect of the standard on their ongoing financial reporting. In March 2016, the FASB issued 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 new guidance is effective for interim and annual periods beginning after December 15, 2016, and early adoption is permitted. This guidance will be applied either prospectively, retrospectively or using a modified retrospective transition method, depending on the area covered in this update. The Companies adopted ASU No. 2016-09 effective January 1, 2017 and it will not have a significant impact on their ongoing financial reporting. In January 2017, the FASB issued ASU No. 2017-04, Simplifying the Test for Goodwill Impairment , which eliminates Step 2 of the goodwill impairment test. Step 2 measures a goodwill impairment loss by computing the implied fair value of a reporting unit's goodwill and comparing it with the carrying amount of that goodwill in the event that the reporting unit does not pass Step 1 of the goodwill impairment test. Under the amendments in this ASU, a goodwill impairment loss would be measured by the amount the carrying value of the reporting unit exceeds its fair value as calculated in Step 1 of the goodwill impairment test. The new guidance is effective for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019, with early adoption permitted for tests performed after January 1, 2017. Great Plains Energy anticipates early adopting ASU No. 2017-04 for its 2017 goodwill impairment test and does not anticipate that it will have a significant impact on its ongoing financial reporting.

Anticipated Acquisition of West

Anticipated Acquisition of Westar Energy, Inc.	12 Months Ended
	Dec. 31, 2016
Anticipated Acquisition of Westar Energy, Inc. [Abstract]
Anticipated Buiness Combination Disclosure [Text Block]	2 . ANTICIPATED ACQUISITION OF WESTAR ENERGY, INC. On May 29, 2016, Great Plains Energy entered into an Agreement and Plan of Merger (Merger Agreement) by and among Great Plains Energy, Westar, and, from and after its accession to the Merger Agreement, GP Star, Inc., a wholly owned subsidiary of Great Plains Energy in the State of Kansas (Merger Sub). Pursuant to the Merger Agreement, subject to the satisfaction or waiver of certain conditions, Merger Sub will merge with and into Westar, with Westar continuing as the surviving corporation. Upon closing, pursuant to the Merger Agreement, Great Plains Energy will acquire Westar for (i) $51.00 in cash and (ii) a number, rounded to the nearest 1/10,000 of a share, of shares of Great Plains Energy common stock, equal to the Exchange Ratio (as described below) 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 Exchange Ratio is calculated as follows: If the volume-weighted average share price of Great Plains Energy common stock on the New York Stock Exchange for the twenty consecutive full trading days ending on (and including) the third trading day immediately prior to the closing date of the merger (the Great Plains Energy Average Stock Price) is: (a) greater than $33.2283 , the Exchange Ratio will be 0.2709 ; (b) greater than or equal to $28.5918 but less than or equal to $33.2283 , the Exchange Ratio will be an amount equal to the quotient obtained by dividing (x) $9.00 by (y) the Great Plains Energy Average Stock Price; or (c) less than $28.5918 , the Exchange Ratio will be 0.3148 . Financing Great Plains Energy plans to finance the cash portion of the merger consideration with equity and debt financing, including (i) $750 million of mandatory convertible preferred equity pursuant to a stock purchase agreement with OCM Credit Portfolio LP (OMERS), (ii) approximately $2.35 billion of equity comprised of a combination of Great Plains Energy common stock and additional mandatory convertible preferred stock, which, as discussed below, was completed in October 2016, and (iii) approximately $4.4 billion in debt. On May 29, 2016, in connection with the Merger Agreement, Great Plains Energy entered into a commitment letter for a 364-day senior unsecured bridge term loan facility in an aggregate principal amount of $8.017 billion (which has subsequently been reduced to $5.1 billion ) to support the anticipated transaction and provide flexibility for the timing of long-term financing. See Note 11 for additional information. On May 29, 2016, Great Plains Energy entered into a stock purchase agreement with OMERS, pursuant to which Great Plains Energy will 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 merger. See Note 14 for additional information. On October 3, 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). Concurrent with this offering, Great Plains Energy also 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). See Note 14 for additional information on the Series B Preferred Stock. Regulatory and Shareholder Approvals Great Plains Energy's anticipated acquisition of Westar was unanimously approved by the Great Plains Energy Board and Westar's Board of Directors (Westar Board). In September 2016, shareholders of Great Plains Energy and Westar approved all proposals necessary for Great Plains Energy's acquisition of Westar at each company's respective shareholder meeting. The anticipated acquisition remains subject to regulatory approvals from The State Corporation Commission of the State of Kansas (KCC), the Public Service Commission of the State of Missouri (MPSC), the Nuclear Regulatory Commission (NRC) and FERC; as well as other customary conditions. KCC Approval In June 2016, Great Plains Energy, KCP&L and Westar filed a joint application with KCC for approval of the anticipated acquisition of Westar by Great Plains Energy. Under applicable Kansas regulations, KCC has 300 days following the filing to rule on the transaction. In December 2016, KCC staff filed its testimony and recommended that the KCC not approve the anticipated acquisition, citing concerns with the size of the acquisition premium, the amount of anticipated cost synergies and potential impacts to the quality of service provided to Kansas customers. In January 2017, Great Plains Energy, KCP&L and Westar filed rebuttal testimony responding to KCC staff's concerns. An evidentiary hearing was held in the case from January 30, 2017 through February 7, 2017 and a final order on the joint application is expected by April 24, 2017. MPSC Approval On February 22, 2017, the MPSC issued an order directing Great Plains Energy to file an application with the MPSC for approval of the anticipated acquisition of Westar. The order requires Great Plains Energy to file the application within ten days from the date of the order. An evidentiary hearing in the case is expected to occur in early April 2017. While there is not a statutory deadline for an MPSC ruling on the merger application, the MPSC has indicated that they intend to work towards a ruling on a timeline that is consistent with the joint application filed by Great Plains Energy, KCP&L and Westar with KCC, where a final order is expected by April 24, 2017. Prior to receiving the MPSC order to file an application for approval of the anticipated acquisition of Westar, Great Plains Energy had reached separate stipulations and agreements with the MPSC staff and the Office of the Public Counsel (OPC) in which the MPSC staff and OPC agreed that they would not file complaints alleging that MPSC approval was necessary in order for Great Plains Energy to acquire Westar. The stipulations and agreements impose certain conditions on Great Plains Energy, KCP&L and GMO in the areas of financing, ratemaking, customer service, corporate social responsibility and also include 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 acquisition and that in the event KCP&L's or GMO's credit ratings are downgraded below investment grade as a result of the acquisition, KCP&L and GMO will be restricted from paying a dividend to Great Plains Energy unless approved by the MPSC or until their credit ratings are restored to investment grade. The stipulations and agreements must still be approved by the MPSC and it is expected that they will be considered as part of Great Plains Energy's application for approval of the anticipated acquisition of Westar. Other Approvals In July 2016, Great Plains Energy and Westar filed applications with FERC and NRC for approval of the merger. In August 2016, the Securities and Exchange Commission (SEC) declared effective a registration statement including a joint proxy statement with Westar (the Proxy Statement Prospectus) used in connection with the Great Plains Energy and Westar special shareholder meetings that occurred in September 2016. In September 2016, shareholders of Great Plains Energy and Westar approved all proposals necessary for Great Plains Energy's acquisition of Westar at each company's respective shareholder meeting. In September 2016, 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 October 2016, the FTC granted Great Plains Energy's request for early termination of the waiting period under the HSR Act with respect to the anticipated acquisition, and the DOJ also notified Great Plains Energy that it has closed its investigation of the antitrust aspects of the anticipated acquisition. In January 2017, The Federal Communications Commission (FCC) consented to the Transfer of Control application filed by Great Plains Energy and Westar relating to the anticipated acquisition. Termination Fees The Merger Agreement provides that in connection with the termination of the Merger Agreement under specified circumstances relating to a failure to obtain required regulatory approvals prior to May 31, 2017 (which date may be extended to November 30, 2017 under certain circumstances (the End Date)), a final and nonappealable order enjoining the consummation of the merger in connection with regulatory approvals or failure by Great Plains Energy to consummate the merger once all of the conditions have been satisfied, Great Plains Energy will be required to pay Westar a termination fee of $380 million . In addition, in the event that the Merger Agreement is terminated by (a) either party because the closing has not occurred by the End Date or (b) Westar, as a result of Great Plains Energy's uncured breach of the Merger Agreement, and prior to such termination, an acquisition proposal for Great Plains Energy is publicly disclosed or made to Great Plains Energy, if Great Plains Energy enters into an agreement or consummates a transaction with respect to an acquisition proposal within twelve months following such termination, then Great Plains Energy may be required to pay Westar a termination fee of $180 million . Similarly, in the event that the Merger Agreement is terminated by (x) either party because the closing has not occurred by the End Date or (y) Great Plains Energy, as a result of Westar's uncured breach of the Merger Agreement, and prior to such termination, an acquisition proposal for Westar is publicly disclosed or made to Westar, if Westar enters into an agreement or consummates a transaction with respect to an acquisition proposal within twelve months following such termination, then Westar may be required to pay Great Plains Energy a termination fee of $280 million .

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2016
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 2016 2015 2014 Cash flows affected by changes in: (millions) Receivables $ (18.3 ) $ 12.5 $ 3.0 Accounts receivable pledged as collateral 2.6 (4.0 ) 4.0 Fuel inventories 9.6 (28.3 ) (13.7 ) Materials and supplies (6.5 ) (3.0 ) (0.4 ) Accounts payable (25.4 ) (11.4 ) 15.2 Accrued taxes 8.1 1.1 8.3 Accrued interest 6.1 3.4 (4.1 ) Deferred refueling outage costs (3.1 ) (6.7 ) 17.0 Pension and post-retirement benefit obligations 27.4 18.5 25.5 Allowance for equity funds used during construction (6.6 ) (4.8 ) (18.0 ) Fuel recovery mechanisms (46.9 ) 47.5 (28.5 ) Solar rebates paid (4.5 ) (9.0 ) (43.2 ) Other 15.2 (2.9 ) (12.3 ) Total other operating activities $ (42.3 ) $ 12.9 $ (47.2 ) Cash paid during the period: Interest $ 191.2 $ 182.2 $ 174.8 Income taxes $ 0.1 $ 0.1 $ — Non-cash investing activities: Liabilities accrued for capital expenditures $ 32.4 $ 35.7 $ 57.4 KCP&L Other Operating Activities Year Ended December 31 2016 2015 2014 Cash flows affected by changes in: (millions) Receivables $ (12.4 ) $ 2.6 $ (18.1 ) Fuel inventories 10.6 (24.7 ) (8.5 ) Materials and supplies (4.3 ) (4.5 ) (1.1 ) Accounts payable (30.5 ) (18.0 ) 20.4 Accrued taxes 67.9 (19.0 ) (42.5 ) Accrued interest — 3.4 (0.1 ) Deferred refueling outage costs (3.1 ) (6.7 ) 17.0 Pension and post-retirement benefit obligations 28.6 18.4 26.9 Allowance for equity funds used during construction (6.6 ) (3.8 ) (16.0 ) Fuel recovery mechanisms (53.7 ) 3.5 (2.2 ) Solar rebates paid (3.1 ) (7.2 ) (17.3 ) Other 4.5 (5.5 ) (23.2 ) Total other operating activities $ (2.1 ) $ (61.5 ) $ (64.7 ) Cash paid during the period: Interest $ 127.0 $ 120.2 $ 112.1 Income taxes $ — $ — $ 30.2 Non-cash investing activities: Liabilities accrued for capital expenditures $ 27.2 $ 23.9 $ 48.8

Receivables

Receivables	12 Months Ended
	Dec. 31, 2016
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 2016 2015 Great Plains Energy (millions) Customer accounts receivable - billed $ 26.2 $ 3.4 Customer accounts receivable - unbilled 79.1 71.6 Allowance for doubtful accounts - customer accounts receivable (4.0 ) (3.8 ) Other receivables 64.7 76.5 Total $ 166.0 $ 147.7 KCP&L Customer accounts receivable - billed $ 25.5 $ 2.8 Customer accounts receivable - unbilled 63.7 58.8 Allowance for doubtful accounts - customer accounts receivable (1.8 ) (1.8 ) Other receivables 51.7 69.4 Total $ 139.1 $ 129.2 Great Plains Energy's and KCP&L's other receivables at December 31, 2016 and 2015 , 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, 2016 and 2015 , Great Plains Energy's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $172.4 million and $175.0 million , respectively. At December 31, 2016 and 2015 , KCP&L's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $110.0 million . KCP&L's agreement expires in September 2017 and allows for $110 million in aggregate outstanding principal amount of borrowings at any time. GMO's agreement expires in September 2017 and allows for $65 million in aggregate outstanding principal of borrowings from mid-November through mid-June and then increases to $80 million from mid-June through mid-November.

Nuclear Plant

Nuclear Plant	12 Months Ended
	Dec. 31, 2016
Nuclear Plant [Abstract]
Nuclear Plant	5. NUCLEAR PLANT KCP&L owns 47% of Wolf Creek Generating Station (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 August 2014 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. KCC MPSC (millions) Current cost of decommissioning (in 2014 dollars) Total Station $ 765.1 $ 765.1 KCP&L's 47% Share 359.6 359.6 Future cost of decommissioning (in 2045-2053 dollars) (a) Total Station $ 2,201.5 $ 2,253.1 KCP&L's 47% Share 1,034.7 1,059.0 Annual escalation factor 3.15% 3.22% Annual return on trust assets (b) 6.29% 5.81% (a) Total future cost over an eight year decommissioning period (b) The 6.29% and 5.81% rate of return for KCC and MPSC, respectively, is through 2025. The rates then systematically decrease through 2053 to 0.72% and 2.22% for KCC and MPSC, respectively, based on the assumption that the fund's investment mix will become increasingly conservative as the decommissioning period approaches. Nuclear Decommissioning Trust Fund In 2016 and 2015, 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. 2016 2015 Decommissioning Trust (millions) Beginning balance January 1 $ 200.7 $ 199.0 Contributions 3.3 3.3 Earned income, net of fees 4.1 3.4 Net realized gains 0.3 0.7 Net unrealized gains (losses) 14.5 (5.7 ) Ending balance December 31 $ 222.9 $ 200.7 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 2016 2015 Cost Basis Unrealized Gains Unrealized Losses Fair Value Cost Basis Unrealized Gains Unrealized Losses Fair Value (millions) Equity securities $ 93.3 $ 62.1 $ (1.5 ) $ 153.9 $ 89.6 $ 47.9 $ (2.1 ) $ 135.4 Debt securities 63.4 2.3 (0.5 ) 65.2 59.6 2.6 (0.5 ) 61.7 Other 3.8 — — 3.8 3.6 — — 3.6 Total $ 160.5 $ 64.4 $ (2.0 ) $ 222.9 $ 152.8 $ 50.5 $ (2.6 ) $ 200.7 The weighted average maturity of debt securities held by the trust at December 31, 2016 , was approximately 8 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. 2016 2015 2014 (millions) Realized gains $ 1.6 $ 5.3 $ 1.4 Realized losses (1.3 ) (4.6 ) (1.0 ) 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 $13.4 billion . This limit of liability consists of the maximum available commercial insurance of $0.4 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 $37.5 million ( $17.6 million , KCP&L's 47% share) per policy year.

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2016
Regulated Operations [Abstract]
Regulatory Matters	6 . REGULATORY MATTERS KCP&L Kansas 2016 Abbreviated Rate Case Proceedings In November 2016, KCP&L filed an abbreviated application with the 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 will not be addressed in this case. Testimony from KCC staff and other parties regarding the case is expected in April 2017, with an evidentiary hearing to occur in May 2017. The decrease to retail revenues is anticipated to be effective in July 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 , 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 November 2016, MPSC staff filed testimony regarding the case stating that they did not have sufficient information to support a change in rates but in the event that new rates were approved, recommended a return on equity of 8.65% , which is on the upper end of their range of 7.9% to 8.75% . In February 2017, KCP&L, MPSC staff and other parties to the case filed a non-unanimous stipulation and agreement resolving certain issues in the case. The stipulation and agreement is pending MPSC approval. An evidentiary hearing also occurred in February 2017. An order on the remaining issues in the case is anticipated to be received to accommodate new rates to be effective in May 2017. GMO Missouri 2016 Rate Case Proceedings In February 2016, GMO filed an application with the MPSC to request an increase to its retail revenues of $59.3 million , with a return on equity of 9.9% and a rate-making equity ratio of 54.83% . The request included recovery of increased transmission and property tax expenses as well as costs for infrastructure and system improvements to continue to provide reliable electric service. In September 2016, GMO, the MPSC staff and certain intervenors reached several non-unanimous stipulations and agreements resolving all issues in the case. In September 2016, the MPSC issued an order for GMO approving the non-unanimous stipulations and agreements and authorizing an increase in annual revenues of $3.0 million and a return on equity of 9.5% to 9.75% . The rates established by the order took effect on February 22, 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 2016 2015 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 $ 125.0 $ 26.4 $ 151.4 Loss on reacquired debt 10.0 (a) 1.7 (a) 11.7 11.3 2.2 13.5 Cost of removal 28.6 — 28.6 12.9 — 12.9 Asset retirement obligations 69.6 24.9 94.5 57.9 19.5 77.4 Pension and post-retirement costs 367.9 (b) 104.7 (b) 472.6 358.5 98.9 457.4 Deferred customer programs 45.9 (c) 27.4 (d) 73.3 50.3 20.8 71.1 Fuel recovery mechanism 69.9 (e) — 69.9 16.3 0.1 16.4 Derivative instruments — — — 0.5 6.3 6.8 Iatan No. 1 and common facilities depreciation and carrying costs 13.6 (f) 5.0 (f) 18.6 14.1 5.2 19.3 Iatan No. 2 construction accounting costs 26.9 (g) 16.1 (g) 43.0 28.7 16.0 44.7 Kansas property tax surcharge 3.6 (e) — 3.6 6.8 — 6.8 Solar rebates 29.2 (e) 41.6 (e) 70.8 33.6 49.0 82.6 Transmission delivery charge 3.1 (e) — 3.1 1.7 — 1.7 La Cygne deferred depreciation 2.8 (h) — 2.8 2.9 — 2.9 Other 6.8 (e) — 6.8 11.9 2.3 14.2 Total $ 801.8 $ 246.2 $ 1,048.0 $ 732.4 $ 246.7 $ 979.1 Regulatory Liabilities Emission allowances $ 62.1 $ — $ 62.1 $ 66.1 $ — $ 66.1 Asset retirement obligations 99.7 — 99.7 86.5 — 86.5 Cost of removal — 65.1 (i) 65.1 — 68.2 68.2 Fuel recovery mechanism — 11.6 11.6 — 5.0 5.0 Pension and post-retirement costs 15.3 7.4 22.7 4.8 3.7 8.5 Other 10.3 38.4 48.7 7.2 42.9 50.1 Total $ 187.4 $ 122.5 $ 309.9 $ 164.6 $ 119.8 $ 284.4 (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, $360.7 million and $65.1 million for KCP&L and GMO, respectively, are not included in rate base and are amortized over various periods. (c) $13.2 million not included in rate base and amortized over various periods. (d) $15.4 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 through 2038 . (g) Included in rate base and amortized through 2058 . (h) Included in rate base and amortized through 2040 . (i) Estimated cumulative net provision for future removal costs.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2016
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, 2016. The goodwill impairment test is a two step process. See Note 1 for additional information regarding the Company's plans to adopt ASU No. 2017-04 for its 2017 goodwill impairment test. The first step compares the fair value of a reporting unit to its carrying amount, including goodwill, to identify potential impairment. If the carrying amount exceeds the fair value of the reporting unit, the second step of the test is performed, consisting of assignment of the reporting unit's fair value to its assets and liabilities to determine an implied fair value of goodwill, which is compared to the carrying amount of goodwill to determine the impairment loss, if any, to be recognized in the financial statements. 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 (EBITDA), 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, 2016 December 31, 2015 Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Great Plains Energy (millions) Computer software $ 355.2 $ (219.1 ) $ 333.0 $ (191.8 ) Asset improvements 28.8 (6.7 ) 28.3 (6.1 ) KCP&L Computer software $ 338.3 $ (203.1 ) $ 315.5 $ (177.7 ) Asset improvements 13.6 (1.8 ) 13.1 (1.5 ) Great Plains Energy's and KCP&L's amortization expense related to intangible assets is detailed in the following table. 2016 2015 (millions) Great Plains Energy $ 29.1 $ 28.6 KCP&L 25.7 24.7 The following table provides the estimated amortization expense related to Great Plains Energy's and KCP&L's intangible assets for 2017 through 2021 for the intangible assets included in the consolidated balance sheets at December 31, 2016 . 2017 2018 2019 2020 2021 (millions) Great Plains Energy $ 26.1 $ 23.7 $ 21.5 $ 18.0 $ 14.3 KCP&L 24.9 23.2 21.0 17.6 13.9

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2016
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. 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. As a result of the CCR rule being published, Great Plains Energy and KCP&L increased their AROs $69.5 million and $51.3 million , respectively, in the second quarter of 2015. The following table summarizes the change in Great Plains Energy's and KCP&L's AROs. Great Plains Energy KCP&L 2016 2015 2016 2015 (millions) Beginning balance $ 275.9 $ 195.9 $ 239.3 $ 177.7 Additions 1.6 54.5 1.3 34.6 Revision in timing and/or estimates 42.1 20.5 40.1 22.2 Settlements (17.4 ) (7.8 ) (15.0 ) (6.7 ) Accretion 13.8 12.8 12.3 11.5 Ending balance $ 316.0 $ 275.9 $ 278.0 $ 239.3 ARO settlement activity in 2016 and 2015 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 Employe

Pension Plans and Other Employee Benefits	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [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 2014, Great Plains Energy incurred pension settlement charges of $8.5 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 2016 2015 2016 2015 Change in projected benefit obligation (PBO) (millions) PBO at January 1 $ 1,154.8 $ 1,186.8 $ 137.5 $ 165.2 Service cost 42.0 45.3 2.6 3.3 Interest cost 52.9 50.3 6.1 6.8 Contribution by participants — — 5.3 6.9 Amendments — — (10.1 ) (7.1 ) Actuarial (gain) loss 65.5 (59.4 ) 0.6 (23.6 ) Benefits paid (70.6 ) (68.2 ) (11.9 ) (14.0 ) PBO at December 31 $ 1,244.6 $ 1,154.8 $ 130.1 $ 137.5 Change in plan assets Fair value of plan assets at January 1 $ 723.9 $ 730.0 $ 114.3 $ 110.6 Actual return on plan assets 51.1 (16.3 ) 2.6 (0.1 ) Contributions by employer and participants 69.8 76.9 10.2 17.6 Benefits paid (68.0 ) (66.7 ) (11.5 ) (13.8 ) Fair value of plan assets at December 31 $ 776.8 $ 723.9 $ 115.6 $ 114.3 Funded status at December 31 $ (467.8 ) $ (430.9 ) $ (14.5 ) $ (23.2 ) Amounts recognized in the consolidated balance sheets Non-current asset $ — $ — $ 9.0 $ 4.5 Current pension and other post-retirement liability (2.2 ) (2.6 ) (0.8 ) (0.8 ) Noncurrent pension liability and other post-retirement liability (465.6 ) (428.3 ) (22.7 ) (26.9 ) Net amount recognized before regulatory treatment (467.8 ) (430.9 ) (14.5 ) (23.2 ) Accumulated OCI or regulatory asset/liability 476.9 461.2 (23.6 ) (9.4 ) Net amount recognized at December 31 $ 9.1 $ 30.3 $ (38.1 ) $ (32.6 ) Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost: Actuarial (gain) loss $ 242.5 $ 230.7 $ (0.7 ) $ (3.3 ) Prior service cost 3.2 3.9 (8.0 ) 3.4 Other 231.2 226.6 (14.9 ) (9.5 ) Net amount recognized at December 31 $ 476.9 $ 461.2 $ (23.6 ) $ (9.4 ) Pension Benefits Other Benefits 2016 2015 2014 2016 2015 2014 Components of net periodic benefit costs (millions) Service cost $ 42.0 $ 45.3 $ 36.7 $ 2.6 $ 3.3 $ 3.7 Interest cost 52.9 50.3 50.1 6.1 6.8 7.9 Expected return on plan assets (49.2 ) (51.7 ) (50.2 ) (3.1 ) (2.9 ) (2.6 ) Prior service cost 0.7 0.8 0.9 1.2 3.1 3.1 Recognized net actuarial (gain) loss 51.8 51.4 50.0 (1.5 ) 0.2 (0.1 ) Transition obligation — — — — 0.2 0.2 Settlement charges — — 8.5 — — — Net periodic benefit costs before regulatory adjustment 98.2 96.1 96.0 5.3 10.7 12.2 Regulatory adjustment (4.9 ) (9.8 ) (11.3 ) 6.0 4.4 4.3 Net periodic benefit costs 93.3 86.3 84.7 11.3 15.1 16.5 Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities Current year net (gain) loss 63.6 8.6 175.8 1.1 (20.6 ) (1.8 ) Amortization of gain (loss) (51.8 ) (51.4 ) (50.0 ) 1.5 (0.2 ) 0.1 Prior service cost — — — (10.2 ) (7.0 ) — Amortization of prior service cost (0.7 ) (0.8 ) (0.9 ) (1.2 ) (3.1 ) (3.1 ) Amortization of transition obligation — — — — (0.2 ) (0.2 ) Other regulatory activity 4.6 4.3 7.3 (5.4 ) (4.4 ) (4.2 ) Total recognized in OCI or regulatory asset/liability 15.7 (39.3 ) 132.2 (14.2 ) (35.5 ) (9.2 ) Total recognized in net periodic benefit costs and OCI or regulatory asset/liability $ 109.0 $ 47.0 $ 216.9 $ (2.9 ) $ (20.4 ) $ 7.3 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 2017 are $0.7 million and $49.7 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 2017 is $0.5 million . The accumulated benefit obligation (ABO) for all defined benefit pension plans was $1,090.2 million and $1,017.6 million at December 31, 2016 , and 2015 , 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. 2016 2015 Pension plans with the PBO in excess of plan assets (millions) Projected benefit obligation $ 1,244.6 $ 1,154.8 Fair value of plan assets 776.8 723.9 Pension plans with the ABO in excess of plan assets Accumulated benefit obligation $ 1,090.2 $ 1,017.6 Fair value of plan assets 776.8 723.9 Other post-retirement benefit plans with the APBO in excess of plan assets Accumulated other post-retirement benefit obligation $ 61.7 $ 108.5 Fair value of plan assets 38.3 80.8 The GMO Supplemental Executive Retirement Plan (SERP) is reflected as an unfunded ABO of $23.6 million . Great Plains Energy has approximately $15.8 million of assets in a non-qualified trust for this plan as of December 31, 2016 , 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 2016 2015 2016 2015 Discount rate 4.31 % 4.54 % 4.20 % 4.47 % 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 2016 2015 2016 2015 Discount rate 4.54 % 4.22 % 4.47 % 4.14 % Expected long-term return on plan assets 7.14 % 7.14 % 2.54 % * 2.81 % * Rate of compensation increase 3.62 % 3.62 % 3.50 % 3.50 % * after tax Great Plains Energy expects to contribute $79.6 million to the pension plans in 2017 to meet 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 2017 , 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 2026. Pension Benefits Other Benefits (millions) 2017 $ 84.9 $ 8.9 2018 81.0 9.4 2019 84.1 10.0 2020 85.9 10.3 2021 87.7 10.7 2022-2026 448.5 58.7 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 34% U.S. large cap and small cap equity securities, 21% international equity securities, 36% fixed income securities, 6% 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, 2016 and 2015 , by asset category are in the following tables. Fair Value Measurements Using Description December 31 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) $ 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 Fair Value Measurements Using Description December 31 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) $ 226.0 $ 195.5 $ — $ — $ 30.5 International (b) 147.4 109.7 — — 37.7 Real estate (c) 45.9 12.2 — — 33.7 Commodities (d) 5.8 — — — 5.8 Fixed income securities Fixed income funds (e) 60.4 20.0 — — 40.4 U.S. Treasury 48.8 48.8 — — — U.S. Agency, state and local obligations 19.0 — 19.0 — — U.S. corporate bonds (f) 108.8 — 108.8 — — Foreign corporate bonds 10.2 — 10.2 — — Hedge funds (g) 23.7 — — — 23.7 Cash equivalents 26.0 26.0 — — — Other 1.9 — 1.9 — — Total $ 723.9 $ 412.2 $ 139.9 $ — $ 171.8 (a) At December 31, 2016 and 2015 , this category is comprised of $128.8 million and $121.6 million , respectively, of traded mutual funds valued at daily listed prices and $84.2 million and $73.9 million , respectively, of traded common stocks and exchange traded funds. At December 31, 2016 and 2015 , this category also includes $34.6 million and $30.5 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, 2016 and 2015 , this category is comprised of $92.8 million and $34.2 million , respectively, of traded mutual funds valued at daily listed prices and $27.6 million and $75.5 million , respectively, of traded American depository receipts, global depository receipts and ordinary shares. At December 31, 2016 and 2015 , this category also includes $43.3 million and $37.7 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, 2016 and 2015, this category is comprised of $12.4 million and $12.2 million , respectively, of traded real estate investment trusts. At December 31, 2016 and 2015 , this category also includes $30.3 million and $33.7 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, 2016 and 2015 , this category is comprised of $20.9 million and $20.0 million , respectively, of traded mutual funds valued at daily listed prices. At December 31, 2016 and 2015 , this category also includes $44.2 million and $40.4 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, 2016 and 2015 , this category is comprised of $115.7 million and $103.0 million , respectively, of corporate bonds, $2.3 million and $2.9 million , respectively, of collateralized mortgage obligations and $2.2 million and $2.9 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, 2016 and 2015 , by asset category are in the following tables. Fair Value Measurements Using Description December 31 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 Fair Value Measurements Using Description December 31 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 $ 3.2 $ 3.2 $ — $ — $ — Fixed income securities Fixed income fund (a) 68.9 0.1 — — 68.8 U.S. Treasury 3.9 3.9 — — — U.S. Agency, state and local obligations 5.4 — 5.4 — — U.S. corporate bonds (b) 15.6 — 15.6 — — Foreign corporate bonds 1.6 — 1.6 — — Cash equivalents 14.0 14.0 — — — Other 1.7 — 1.7 — — Total $ 114.3 $ 21.2 $ 24.3 $ — $ 68.8 (a) At December 31, 2015 , this category is comprised of $0.1 million of traded mutual funds valued at daily listed prices. At December 31, 2016 and 2015 , this category also includes $62.7 million and $68.8 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, 2016 and 2015 , this category is comprised of $14.0 million and $12.6 million , respectively, of corporate bonds, $0.5 million and $0.6 million , respectively, of collateralized mortgage obligations and $3.3 million and $2.4 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 2016 and 2017 was 6.8% and 6.5% , respectively, with the rate declining through 2025 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, 2016 , are detailed in the following table. Increase Decrease (millions) Effect on total service and interest component $ 0.8 $ (0.7 ) Effect on post-retirement benefit obligation 1.0 (0.8 ) 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 $11.5 million in 2016 , $10.6 million in 2015 and $9.7 million in 2014 . KCP&L's annual cost of the plans was approximately $8.0 million in 2016 , $7.9 million in 2015 and $7.1 million in 2014 .

Equity Compensation

Equity Compensation	12 Months Ended
	Dec. 31, 2016
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, limited stock appreciation rights, director shares, director deferred share units and performance shares 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 has a policy of delivering newly issued shares, or shares surrendered by Long-Term Incentive Plan participants for the withholding of taxes and held in treasury, or both, and does not expect to repurchase common shares during 2017 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. 2016 2015 2014 Great Plains Energy (millions) Equity compensation expense $ 5.0 $ 4.0 $ 9.9 Income tax benefit 1.6 1.4 3.6 KCP&L Equity compensation expense $ 3.2 $ 2.6 $ 6.9 Income tax benefit 1.0 0.9 2.4 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 2016 , inputs for expected volatility, dividend yield and risk-free rates were 18% , 3.61% and 0.94% , 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, 2016 609,010 $ 25.60 Granted 225,204 31.41 Earned (306,953 ) 24.22 Forfeited (1,714 ) 27.61 Performance adjustment 99,553 24.16 Ending balance December 31, 2016 625,100 28.13 * weighted-average At December 31, 2016 , the remaining weighted-average contractual term was 1.1 years. The weighted-average grant-date fair value of shares granted was $31.41 , $24.03 and $28.78 in 2016, 2015 and 2014, respectively. At December 31, 2016 , there was $6.4 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 $7.4 million , $0.5 million and $2.8 million in 2016 , 2015 and 2014, 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, 2016 231,508 $ 24.78 Granted and issued 96,053 29.41 Vested (77,317 ) 22.69 Forfeited (572 ) 27.51 Ending balance December 31, 2016 249,672 27.20 * weighted-average At December 31, 2016 , the remaining weighted-average contractual term was 1.2 years. The weighted-average grant-date fair value of shares granted was $29.41 , $25.89 and $25.70 in 2016, 2015 and 2014, respectively. At December 31, 2016 , there was $2.6 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 $1.8 million , $2.2 million and $1.9 million in 2016, 2015 and 2014, 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 2016 and 2015 . Director Deferred Share Units activity is summarized in the following table. Share Units Grant Date Fair Value* Beginning balance January 1, 2016 115,415 $ 22.95 Issued 23,172 28.99 Ending balance December 31, 2016 138,587 23.96 * weighted-average

Short-term Borrowings and Short

Short-term Borrowings and Short-term Bank Lines of Credit	12 Months Ended
	Dec. 31, 2016
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, 2016 , Great Plains Energy was in compliance with this covenant. In June 2016, the facility was amended, among other things, to increase the maximum consolidated indebtedness to consolidated capitalization ratio of 0.65 to 1.00 to a level such that, if Great Plains Energy would not be in compliance with the covenant as of the date of the closing of the anticipated acquisition of Westar, the ratio would increase up to a maximum of 0.75 to 1.00 for one year. 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. At December 31, 2015 , Great Plains Energy had $10.0 million of outstanding cash borrowings at a weighted-average interest rate of 1.94% and had issued $0.2 million 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, 2016 , KCP&L was in compliance with this covenant. 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. At December 31, 2015 , KCP&L had $180.3 million of commercial paper outstanding at a weighted-average interest rate of 0.70% , had issued letters of credit totaling $2.7 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, 2016 , GMO was in compliance with this covenant. 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. At December 31, 2015 , GMO had $43.7 million of commercial paper outstanding at a weighted-average interest rate of 0.65% , had issued letters of credit totaling $2.5 million and had no outstanding cash borrowings under the credit facility. Great Plains Energy's $5.1 Billion Term Loan Facility In connection with the 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. The aggregate principal amount of the facility has been reduced most recently in connection with the October 2016 Great Plains Energy common stock and depositary share offerings. As of December 31, 2016, the available aggregate principal amount of the facility was $5.1 billion .

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2016
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 2016 2015 KCP&L (millions) General Mortgage Bonds 2.47% EIRR bonds (a) 2017-2035 $ 110.5 $ 110.5 7.15% Series 2009A (8.59% rate) (b) 2019 400.0 400.0 Senior Notes 5.85% Series (5.72% rate) (b) 2017 250.0 250.0 6.375% Series (7.49% rate) (b) 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) (b) 2035 250.0 250.0 5.30% Series 2041 400.0 400.0 EIRR Bonds 0.694% Series 2007A and 2007B (c) 2035 146.5 146.5 2.875% Series 2008 2038 23.4 23.4 Current maturities (281.0 ) — Unamortized discount and debt issuance costs (15.4 ) (17.3 ) Total KCP&L excluding current maturities (d) 2,284.0 2,563.1 Other Great Plains Energy GMO First Mortgage Bonds 9.44% Series 2017-2021 5.7 6.8 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) (b) 2017 100.0 100.0 4.85% Series 2021 350.0 350.0 5.292% Series 2022 287.5 287.5 Current maturities (101.1 ) (1.1 ) Unamortized discount and premium, net and debt issuance costs (1.8 ) (2.1 ) Total Great Plains Energy excluding current maturities (d) $ 3,365.2 $ 3,745.1 (a) Weighted-average interest rates at December 31, 2016 (b) Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments (c) Variable rate (d) At December 31, 2016 and 2015, 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. 2016 2015 2014 (millions) KCP&L $ 3.2 $ 3.0 $ 3.0 Other Great Plains Energy 30.6 1.1 1.8 Total Great Plains Energy $ 33.8 $ 4.1 $ 4.8 In 2016, Other Great Plains Energy includes $29.6 million of amortization of debt expense related to Great Plains Energy's $5.1 billion bridge term loan facility. Fees related to this facility are being amortized over the 364 day term of the facility. KCP&L General Mortgage Bonds KCP&L has issued mortgage bonds under the General Mortgage Indenture and Deed of Trust dated December 1, 1986, as supplemented (Indenture). The Indenture creates a mortgage lien on substantially all of KCP&L's utility plant. Mortgage bonds totaling $510.5 million were outstanding at December 31, 2016 and 2015, respectively. 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, 2016, 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 Standard & Poor's 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 $5.7 million and $6.8 million , respectively, were outstanding at December 31, 2016 and 2015. 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, 2016, GMO was in compliance with these covenants. 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. 2017 2018 2019 2020 2021 (millions) Great Plains Energy $ 382.1 $ 351.1 $ 401.1 $ 1.1 $ 432.0 KCP&L 281.0 350.0 400.0 — —

Common Shareholders' Equity

Common Shareholders' Equity	12 Months Ended
	Dec. 31, 2016
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. 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 plans to use proceeds from the offering to finance a portion of the cash consideration for the anticipated acquisition of Westar. 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, 2016, 1.0 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, 2016, 0.7 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. In addition, if preferred stock dividends are not declared and paid when scheduled, Great Plains Energy could not declare or pay common stock dividends or purchase any common shares. If the unpaid preferred stock dividends are in arrears for six or more quarters, whether or not consecutive, the preferred shareholders will be entitled to name two directors to the Great Plains Energy Board. 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, except as the ratio pertains to Great Plains Energy, which was amended in June 2016, as further described in Note 11. As of December 31, 2016, 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, 2016. The restrictions are not expected to affect the Companies' ability to pay dividends at the current level in the foreseeable future.

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2016
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock [Text Block]	14 . PREFERRED STOCK At December 31, 2016, 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 Preference Stock without par value were authorized under Great Plains Energy's articles of incorporation. At December 31, 2016, Great Plains Energy had 862,500 shares of Series B Preferred Stock issued and outstanding and had entered into a stock purchase agreement to issue 750,000 shares of Series A Preferred Stock at the closing of the anticipated acquisition with Westar. In August 2016, Great Plains Energy redeemed its 390,000 shares of outstanding Cumulative Preferred Stock, $100 par value. See the discussion below for further information on these transactions and the pertinent rights and privileges of the Series A and Series B Preferred Stock. 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 will 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 merger. The stock purchase agreement is subject to various closing conditions. Each share of Series A Preferred Stock shall automatically convert three years after issuance into a number of shares of Great Plains Energy common stock equal to the Conversion Rate. The Conversion Rate is calculated as follows: If the average volume-weighted average price per share of Great Plains Energy common stock over 20 consecutive trading days commencing on the 22nd trading day prior to the date of conversion (Applicable Market Value) is: (a) Equal to or greater than $34.38 , the Conversion Rate shall be 29.0855 ; (b) Less than $34.38 but greater than $28.65 , the Conversion Rate shall be $1,000 divided by the Applicable Market Value; or (c) Less than or equal to $28.65 , the Conversion Rate shall be 34.9026 . OMERS can voluntarily convert its Series A Preferred Stock into Great Plains Energy common stock at any time at the 29.0855 Conversion Rate, subject to obtaining all necessary governmental approvals. The Series A Preferred Stock is entitled to a 7.25% annual dividend, payable in cash, Great Plains Energy common stock or a combination thereof. The Series A Preferred Stock has a liquidation preference of $1,000 per share. OMERS will be entitled to name two directors to the Great Plains Energy Board if dividends payable with respect to the Series A Preferred Stock are in arrears for two quarters and one observer on the Great Plains Energy Board if Great Plains Energy's credit rating is downgraded to below investment grade, so long as OMERS holds 50 percent of its original investment and subject to all necessary governmental approvals being obtained. 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 plans to use proceeds from the offering to fund a portion of the cash consideration for the anticipated acquisition of Westar. Each depositary share entitles 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 will automatically convert into a number of shares of Great Plains Energy common stock equal to the Conversion Rate. The Conversion Rate is calculated as follows: If the volume-weighted average price per share, subject to certain anti-dilution adjustments, of Great Plains Energy common stock over 20 consecutive trading days commencing on the 22nd trading day prior to the date of conversion (Applicable Market Value) is: (a) Equal to or greater than $31.74 , the Conversion Rate shall be 31.5060 ; (b) Less than $31.74 but greater than $26.45 , the Conversion Rate shall be $1,000 divided by the Applicable Market Value; or (c) Less than or equal to $26.45 , the Conversion Rate shall be 37.8080 . At any time prior to September 15, 2019, a holder may elect to convert shares of the Series B Preferred Stock in whole or in part (but not less than one share of Series B Preferred Stock) into shares of Great Plains Energy common stock at the 31.5060 Conversion Rate. Dividends on the Series B Preferred Stock will be 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. Holders of the Series B Preferred Stock will be entitled to name two directors to the Great Plains Energy Board if dividends payable with respect to the Series B Preferred Stock are in arrears for six or more quarters, whether or not consecutive. Cumulative Preferred Stock In August 2016, Great Plains Energy redeemed its 390,000 shares of outstanding Cumulative Preferred Stock, par value $100 per share, for a total redemption price of $40.1 million . Great Plains Energy redeemed all outstanding shares of its (i) 3.80% Preferred for $103.70 per share, plus accrued and unpaid dividends of $0.75 per share, for a total redemption price of $104.45 per share, (ii) 4.50% Preferred for $101.00 per share, plus accrued and unpaid dividends of $0.89 per share, for a total redemption price of $101.89 per share, (iii) 4.20% Preferred for $102.00 per share, plus accrued and unpaid dividends of $0.83 per share, for a total redemption price of $102.83 per share and (iv) 4.35% Preferred for $101.00 per share, plus accrued and unpaid dividends of $0.86 per share, for a total redemption price of $101.86 per share.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
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 four 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. 2017 2018 2019 2020 (millions) Great Plains Energy $ 43.4 $ 36.6 $ 11.5 $ 14.0 KCP&L 34.9 16.5 7.6 13.0 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 Environmental Protection Agency (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 (CO 2 ) per MWh, or approximately 19 million tons and 15 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 CO 2 , could be enacted in the future. At the international level, in December 2015 the Paris Agreement was adopted by nearly 200 countries and became effective in November 2016 as the threshold of at least 55 countries representing at least 55% of global greenhouse gas emissions have joined it through ratification. The Paris Agreement does not result in any new, legally binding obligations on the United States to meet a particular greenhouse gas emissions target, but establishes a framework for international cooperation on climate change. Other international agreements legally binding on the United States 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 CO 2 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. In August 2015, the EPA finalized its Clean Power Plan which sets CO 2 emission performance rates for existing affected fossil fuel-fired electric generating units. Specifically, the EPA translated those performance rates into a state goal measured in mass and rate based on each state's generation mix. The states have the ability to develop their own plans for affected units to achieve either the performance rates directly or the state goals, with guidelines for the development, submittal and implementation of those plans. Nationwide, by 2030, the EPA projects the Clean Power Plan would achieve CO 2 emission reductions from the power sector of approximately 32% from CO 2 emission levels in 2005. The EPA has finalized an interim CO 2 goal rate reduction in Kansas and Missouri (average of 2022-2029) of 34% and 26% , respectively, and 2030 targets in Kansas and Missouri of 44% and 37% , respectively. The baseline for these reductions is 2012 CO 2 emissions adjusted by the EPA. The EPA has also finalized mass based CO 2 reduction goals. States are required to submit plans to implement the Clean Power Plan. An EPA plan with either a rate-based or mass-based trading program has yet to be finalized and can be enforced in states that fail to submit approved plans. 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 United States Court of Appeals for the District of Columbia Circuit and any subsequent review by the U.S. Supreme Court if such review is sought. Compliance with the Clean Power Plan 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 pending litigation is known and/or the state plans to implement the Clean Power Plan are 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. Future water permit renewals at KCP&L's Iatan Station and at GMO's Sibley and Lake Road Stations could also be impacted by the allowable amount of heat that can be contained in the returned water. Great Plains Energy and KCP&L cannot predict the outcome of these matters; however, while less significant outcomes are possible, these matters 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. In September 2015, the EPA finalized a revision of the technology-based effluent limitations guidelines and standards regulation to make the existing controls on discharges from steam electric power plants more stringent. The final rule sets the first federal limits on the levels of toxic metals in wastewater that can be discharged from power plants. The new requirements for existing power plants would be phased in between 2018 and 2023. The final rule establishes new or additional requirements for wastewaters associated with the following processes and byproducts at certain KCP&L and GMO stations: flue gas desulfurization, fly ash, bottom ash, flue gas mercury control, and combustion residual leachate from landfills and surface impoundments. Estimated capital costs to comply with the final rule are included in the estimated capital expenditures table above. 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 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, 2016 and 2015 , 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, 2016 and 2015 , Great Plains Energy had $1.4 million 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 $1.5 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. 2016 2015 2014 (millions) Great Plains Energy $ 15.0 $ 16.8 $ 16.0 KCP&L 13.7 15.0 14.0 Great Plains Energy's and KCP&L's contractual commitments at December 31, 2016 , excluding pensions and long-term debt, are detailed in the following tables. Great Plains Energy 2017 2018 2019 2020 2021 After 2021 Total Lease commitments (millions) Operating lease $ 12.9 $ 11.0 $ 9.3 $ 9.7 $ 9.7 $ 110.5 $ 163.1 Capital lease 0.4 0.4 0.4 0.4 0.4 3.1 5.1 Purchase commitments Fuel 259.0 145.8 62.2 53.8 11.2 100.8 632.8 Power 47.3 47.3 47.3 47.3 47.4 462.2 698.8 Other 50.1 32.0 33.3 5.9 6.5 38.7 166.5 Total contractual commitments $ 369.7 $ 236.5 $ 152.5 $ 117.1 $ 75.2 $ 715.3 $ 1,666.3 KCP&L 2017 2018 2019 2020 2021 After 2021 Total Lease commitments (millions) Operating lease $ 12.0 $ 11.0 $ 9.3 $ 9.7 $ 9.7 $ 110.5 $ 162.2 Capital lease 0.2 0.2 0.2 0.2 0.2 1.6 2.6 Purchase commitments Fuel 221.5 119.4 43.6 35.1 1.8 100.8 522.2 Power 34.8 34.8 34.8 34.8 34.9 324.9 499.0 Other 49.3 31.1 30.6 5.0 5.6 33.0 154.6 Total contractual commitments $ 317.8 $ 196.5 $ 118.5 $ 84.8 $ 52.2 $ 570.8 $ 1,340.6 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 $1.5 million in 2017, $1.2 million in 2018 and approximately $0.4 million per year from 2019 to 2025 , for a total of $5.5 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

Legal Proceedings	12 Months Ended
	Dec. 31, 2016
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. Because MPS Merchant was a net purchaser of power during the refund period, it has received approximately $8 million in refunds through settlements with certain sellers of power. MPS Merchant estimates that it is entitled to approximately $12 million in additional refunds under the standards FERC has used in this case once a comprehensive resettlement of those markets occurs, as required by FERC. FERC has stated that interest will be applied to the refunds but the amount of interest has not yet been determined. 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. MPS Merchant (and other parties) filed a request for rehearing challenging FERC's findings of tariff violations and the remedy imposed in the November 2014 order. Additionally, several parties representing California utilities and governmental agencies filed a request for clarification or rehearing focusing on the remedy. In November 2015, FERC issued an order denying MPS Merchant's request for rehearing and expanded the remedy to include additional MPS Merchant sales in the California markets. MPS Merchant filed another request for rehearing, challenging the expanded remedy. In February 2016, FERC issued an order expanding the amount of revenues that MPS Merchant would be required to disgorge to include all revenues in excess of the FERC-determined competitive market clearing price for all sales in the California markets during the Summer Period that occurred in any hour in which any remaining respondent in the proceeding was found to have committed a tariff violation. In October 2016, MPS Merchant reached a settlement agreement 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. The settlement agreement was filed with FERC in December 2016. In accordance with the terms of the settlement agreement, the $7.5 million of cash consideration will begin accruing interest at the FERC interest rate beginning on January 1, 2017, until the date paid. In January 2017, FERC issued an order denying a motion filed in conjunction with and as a condition of the settlement agreement and ordered MPS Merchant and the California utilities and governmental agencies to notify FERC by February 27, 2017 whether they intended to revise the settlement agreement or withdraw it. In February 2017, MPS Merchant and the California utilities and governmental agencies filed a notice with FERC revising the settlement agreement to waive the condition of the settlement agreement that was contingent upon the motion denied by FERC. The revised settlement agreement is subject to approval by the Public Utilities Commission of the State of California and FERC. As a result of the developments noted above, Great Plains Energy recorded a $7.5 million loss in other operating expenses in 2016.

Guarantees

Guarantees	12 Months Ended
	Dec. 31, 2016
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, 2016 , Great Plains Energy has provided $135.3 million of credit support for GMO as follows: • Great Plains Energy direct guarantees to GMO counterparties totaling $38.7 million , which expire in 2017 and 2018 and • Great Plains Energy guarantee of GMO long-term debt totaling $96.6 million , which includes debt with maturity dates ranging from 2017 to 2023 . Great Plains Energy has also guaranteed GMO's commercial paper program . At December 31, 2016 , GMO had $201.9 million commercial paper outstanding.

Related Party Transactions and

Related Party Transactions and Relationships	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Related Party Transactions and Relationships	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 $194.4 million for 2016, $183.6 million for 2015 and $173.9 million for 2014. Additionally, KCP&L and GMO engage in wholesale electricity transactions with each other. KCP&L's net wholesale sales to GMO were $0.8 million , $0.2 million and $12.7 million in 2016, 2015 and 2014, respectively. 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, 2016 and 2015, 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 2016 2015 (millions) Net receivable from GMO $ 64.6 $ 50.0 Net receivable from Great Plains Energy 2.6 15.8

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	19 . DERIVATIVE INSTRUMENTS Great Plains Energy and KCP&L are exposed to a variety of market risks including interest rates and commodity prices. Management has established risk management policies and strategies to reduce the potentially adverse effects that the volatility of the markets may have on Great Plains Energy's and KCP&L's operating results. Great Plains Energy's and KCP&L's interest rate risk management activities have included using derivative instruments to hedge against future interest rate fluctuations on anticipated debt issuances. Commodity risk management activities, including the use of certain derivative instruments, are subject to the management, direction and control of an internal commodity risk committee. Management maintains commodity price risk management strategies that use derivative instruments to reduce the effects of fluctuations in wholesale sales and fuel and purchased power expense caused by commodity price volatility. Counterparties to commodity derivatives expose Great Plains Energy and KCP&L to credit loss in the event of nonperformance. This credit loss is limited to the cost of replacing these contracts at current market rates. Derivative instruments, excluding those instruments that qualify for the NPNS election, which are accounted for by accrual accounting, are recorded on the balance sheet at fair value as an asset or liability. Changes in the fair value of derivative instruments are recognized in net income, except hedges for KCP&L's and GMO's utility operations that are recorded to a regulatory asset or liability consistent with KCC and MPSC regulatory orders. For derivative contracts with counterparties under master netting arrangements, Great Plains Energy and KCP&L can net receivables and payables with each respective counterparty. Interest Rate Risk Management 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 anticipated acquisition of Westar. Settlement of the interest rate swaps is contingent on the consummation of the anticipated acquisition of Westar. The interest rate swaps have been designated as economic hedges (non-hedging derivatives). The fair values of these instruments are recorded as derivative assets or liabilities with an offsetting entry recorded to interest charges. Commodity Risk Management KCP&L and GMO have Transmission Congestion Rights (TCRs) that they utilize to hedge against congestion costs and protect load prices in the Southwest Power Pool, Inc. (SPP) Integrated Marketplace. These financial contracts have been designated as economic hedges (non-hedging derivatives). The fair values of these instruments are recorded as derivative assets or liabilities with an offsetting entry recorded to a regulatory asset or liability. The settlement costs are included in a recovery mechanism. A regulatory asset or liability is recorded to reflect the change in the timing of recognition authorized by KCC and MPSC. Recovery of actual costs will not impact earnings, but will impact cash flows due to the timing of the recovery mechanism. MPS Merchant, which has certain long-term natural gas contracts remaining from its former non-regulated trading operations, manages the daily delivery of its remaining contractual commitments with economic hedges (non-hedging derivatives) to reduce its exposure to changes in market prices. Within the trading portfolio, MPS Merchant takes certain positions to hedge physical sale or purchase contracts. MPS Merchant records the fair value of physical trading energy contracts as derivative assets or liabilities with an offsetting entry to the consolidated statements of comprehensive income. The gross notional contract amount and recorded fair values of open positions for derivative instruments are summarized in the following table. The fair values of these derivatives are recorded on the consolidated balance sheets. The fair values below are gross values before netting agreements and netting of cash collateral. December 31 2016 2015 Notional Contract Amount Fair Value Notional Contract Amount Fair Value Great Plains Energy (millions) Non-hedging derivatives Futures contracts $ — $ — $ 26.6 $ (5.7 ) Forward contracts 9.8 2.4 15.6 3.1 Transmission congestion rights 3.7 1.3 5.6 (0.5 ) Interest rate swaps 4,415.0 79.3 — — KCP&L Non-hedging derivatives Futures contracts $ — $ — $ 0.9 $ (0.1 ) Transmission congestion rights 2.7 0.9 4.1 (0.4 ) The fair values of Great Plains Energy's and KCP&L's open derivative positions and balance sheet classification are summarized in the following tables. The fair values below are gross values before netting agreements and netting of cash collateral. Great Plains Energy Balance Sheet Asset Derivatives Liability Derivatives December 31, 2016 Classification Fair Value Fair Value Derivatives Not Designated as Hedging Instruments (millions) Commodity contracts Derivative instruments/Other $ 4.3 $ 0.6 Interest rate contracts Derivative instruments 79.3 — December 31, 2015 Derivatives Not Designated as Hedging Instruments Commodity contracts Other/Derivative instruments $ 3.3 $ 6.4 KCP&L Balance Sheet Asset Derivatives Liability Derivatives December 31, 2016 Classification Fair Value Fair Value Derivatives Not Designated as Hedging Instruments (millions) Commodity contracts Other $ 1.3 $ 0.4 December 31, 2015 Derivatives Not Designated as Hedging Instruments Commodity contracts Other $ 0.2 $ 0.7 The following tables provide information regarding Great Plains Energy's and KCP&L's offsetting of derivative assets and liabilities. Great Plains Energy Gross Amounts Not Offset in the Statement of Financial Position Description Gross Amounts Recognized Gross Amounts Offset in the Statement of Financial Position Net Amounts Presented in the Statement of Financial Position Financial Instruments Cash Collateral Net Amount December 31, 2016 (millions) Derivative assets $ 83.6 $ (0.5 ) $ 83.1 $ — $ — $ 83.1 Derivative liabilities 0.6 (0.5 ) 0.1 — — 0.1 December 31, 2015 Derivative assets $ 3.3 $ (0.2 ) $ 3.1 $ — $ — $ 3.1 Derivative liabilities 6.4 (5.9 ) 0.5 — — 0.5 KCP&L Gross Amounts Not Offset in the Statement of Financial Position Description Gross Amounts Recognized Gross Amounts Offset in the Statement of Financial Position Net Amounts Presented in the Statement of Financial Position Financial Instruments Cash Collateral Net Amount December 31, 2016 (millions) Derivative assets $ 1.3 $ (0.4 ) $ 0.9 $ — $ — $ 0.9 Derivative liabilities 0.4 (0.4 ) — — — — December 31, 2015 Derivative assets $ 0.2 $ (0.2 ) $ — $ — $ — $ — Derivative liabilities 0.7 (0.3 ) 0.4 — — 0.4 At December 31, 2015, Great Plains Energy had offset $5.7 million of cash collateral posted with counterparties against net derivative positions. See Note 21 for information regarding amounts reclassified out of accumulated other comprehensive loss for Great Plains Energy and KCP&L. Great Plains Energy's accumulated OCI at December 31, 2016 , includes $7.8 million that is expected to be reclassified to expenses over the next twelve months. KCP&L's accumulated OCI at December 31, 2016 , includes $7.5 million that is expected to be reclassified to expenses over the next twelve months. The following tables summarize the amounts of gain (loss) recognized for the change in fair value of derivatives not designated as hedging instruments for Great Plains Energy and KCP&L. Great Plains Energy Derivatives Not Designated as Hedging Instruments 2016 2015 2014 Location of Gain (Loss) (millions) Electric revenues $ 3.5 $ (8.2 ) $ (14.2 ) Fuel and purchased power (2.7 ) (4.0 ) (3.4 ) Interest charges 79.3 — — Regulatory asset — (6.8 ) (2.7 ) Regulatory liability 1.3 — — Total $ 81.4 $ (19.0 ) $ (20.3 ) KCP&L Derivatives Not Designated as Hedging Instruments 2016 2015 2014 Location of Gain (Loss) (millions) Electric revenues $ 3.5 $ (8.2 ) $ (14.2 ) Fuel and purchased power 0.1 1.5 1.1 Regulatory asset — (0.5 ) (0.2 ) Regulatory liability 1.0 — — Total $ 4.6 $ (7.2 ) $ (13.3 )

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	20. 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. 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, 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, 2015 , 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 KCP&L's long-term debt, including current maturities, were $2.6 billion and $2.7 billion , respectively. At December 31, 2015, 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. 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. The fair values below are gross values before netting arrangements and netting of cash collateral. Description December 31 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 — Derivative instruments - commodity (c) 1.3 — — 1.3 Total $ 235.5 $ 192.1 $ 42.1 $ 1.3 Liabilities Derivative instruments - commodity (c) 0.4 — — 0.4 Total $ 0.4 $ — $ — $ 0.4 Other Great Plains Energy Assets Derivative instruments Commodity (c) $ 3.0 $ — $ 2.2 $ 0.8 Interest rate (d) 79.3 — — 79.3 Total $ 82.3 $ — $ 2.2 $ 80.1 Liabilities Derivative instruments - commodity (c) 0.2 — 0.1 0.1 Total $ 0.2 $ — $ 0.1 $ 0.1 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 — Derivative instruments (c)(d) 83.6 — 2.2 81.4 Total $ 317.8 $ 192.1 $ 44.3 $ 81.4 Liabilities Derivative instruments (c) 0.6 — 0.1 0.5 Total $ 0.6 $ — $ 0.1 $ 0.5 Description December 31 Level 1 Level 2 Level 3 KCP&L (millions) Assets Nuclear decommissioning trust (a) Equity securities $ 135.4 $ 135.4 $ — $ — Debt securities U.S. Treasury 26.4 26.4 — — U.S. Agency 1.8 — 1.8 — State and local obligations 4.0 — 4.0 — Corporate bonds 29.2 — 29.2 — Foreign governments 0.3 — 0.3 — Cash equivalents 3.6 3.6 — — Total nuclear decommissioning trust 200.7 165.4 35.3 — Self-insured health plan trust (b) Equity securities 1.1 1.1 — — Debt securities 7.3 — 7.3 — Cash and cash equivalents 5.2 5.2 — — Total self-insured health plan trust 13.6 6.3 7.3 — Derivative instruments - commodity (c) 0.2 — — 0.2 Total $ 214.5 $ 171.7 $ 42.6 $ 0.2 Liabilities Derivative instruments - commodity (c) 0.7 0.1 — 0.6 Total $ 0.7 $ 0.1 $ — $ 0.6 Other Great Plains Energy Assets Derivative instruments - commodity (c) $ 3.1 $ — $ 2.7 $ 0.4 SERP rabbi trusts (e) Equity securities 0.1 0.1 — — Total $ 3.2 $ 0.1 $ 2.7 $ 0.4 Liabilities Derivative instruments - commodity (c) 5.7 5.6 — 0.1 Total $ 5.7 $ 5.6 $ — $ 0.1 Great Plains Energy Assets Nuclear decommissioning trust (a) $ 200.7 $ 165.4 $ 35.3 $ — Self-insured health plan trust (b) 13.6 6.3 7.3 — Derivative instruments (c) 3.3 — 2.7 0.6 SERP rabbi trusts (e) 0.1 0.1 — — Total $ 217.7 $ 171.8 $ 45.3 $ 0.6 Liabilities Derivative instruments (c) 6.4 5.7 — 0.7 Total $ 6.4 $ 5.7 $ — $ 0.7 (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) The fair value of commodity derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlations among fuel prices, net of estimated credit risk. Derivative instruments classified as Level 1 represent exchange traded derivative instruments. Derivative instruments classified as Level 2 represent non-exchange traded derivative instruments valued using pricing models for which observable market data is available to corroborate the valuation inputs. Derivative instruments classified as Level 3 represent non-exchange traded derivative instruments valued using pricing models for which observable market data is not available to corroborate the valuation inputs and TCRs valued at the most recent auction price in the SPP Integrated Marketplace. (d) 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 LIBOR swap rates. As of December 31, 2016, the calculated net present value was 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 settlement of these instruments. See Note 19 for more details on the interest rate swaps. A decrease in the contingency factor would result in a higher fair value measurement. Management expects that the contingency factor will decrease as the Company obtains certain regulatory approvals connected with the anticipated acquisition of Westar and due to the passage of time. Because of the unobservable nature of the contingency factor, the interest rate derivatives have been classified as Level 3. (e) At December 31, 2016 and 2015, the Supplemental Executive Retirement Plan (SERP) rabbi trusts also included $16.0 million and $16.6 million , respectively, of fixed income funds valued at NAV 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 reconcile the beginning and ending balances for all Level 3 assets and liabilities measured at fair value on a recurring basis. Great Plains Energy Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative Instruments 2016 2015 (millions) Net asset (liability) at January 1 $ (0.1 ) $ 3.5 Total realized/unrealized gains (losses): included in electric revenue 3.5 (8.2 ) included in fuel and purchased power expense 0.8 (1.5 ) included in non-operating income 11.3 8.6 included in interest charges 79.3 — included in regulatory (asset) liability 1.3 (0.5 ) Purchases 0.3 — Settlements (15.5 ) (2.0 ) Net asset (liability) at December 31 $ 80.9 $ (0.1 ) Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at December 31: included in non-operating income $ 0.1 $ (0.2 ) included in interest charges 79.3 — included in regulatory (asset) liability 1.3 (0.5 ) KCP&L Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative Instruments 2016 2015 (millions) Net asset (liability) at January 1 $ (0.4 ) $ 3.1 Total realized/unrealized gains (losses): included in electric revenue 3.5 (8.2 ) included in regulatory (asset) liability 1.0 (0.4 ) Purchases (0.3 ) (0.8 ) Settlements (2.9 ) 5.9 Net asset (liability) at December 31 $ 0.9 $ (0.4 ) Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at December 31: included in regulatory (asset) liability $ 1.0 $ (0.4 )

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss) [Text Block]	21 . ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) The following tables reflect the change in the balances of each component of accumulated other comprehensive 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) 2016 Beginning balance January 1 $ (10.1 ) $ (1.9 ) $ (12.0 ) Other comprehensive income (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 5.6 (0.2 ) 5.4 Ending balance December 31 $ (4.5 ) $ (2.1 ) $ (6.6 ) 2015 Beginning balance January 1 $ (15.8 ) $ (2.9 ) $ (18.7 ) Other comprehensive income before reclassifications — 0.6 0.6 Amounts reclassified from accumulated other comprehensive loss 5.7 0.4 6.1 Net current period other comprehensive income 5.7 1.0 6.7 Ending balance December 31 $ (10.1 ) $ (1.9 ) $ (12.0 ) (a) Net of tax KCP&L Gains and Losses on Cash Flow Hedges (a) (millions) 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 ) 2015 Beginning balance January 1 $ (14.9 ) Amounts reclassified from accumulated other comprehensive loss 5.3 Net current period other comprehensive income 5.3 Ending balance December 31 $ (9.6 ) (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 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 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (9.2 ) $ (9.2 ) Interest charges (9.2 ) (9.2 ) Income before income tax expense and income from equity investments 3.6 3.5 Income tax benefit $ (5.6 ) $ (5.7 ) Net income Amortization of defined benefit pension items Net losses included in net periodic benefit costs $ (0.8 ) $ (0.7 ) Utility operating and maintenance expenses (0.8 ) (0.7 ) Income before income tax expense and income from equity investments 0.3 0.3 Income tax benefit $ (0.5 ) $ (0.4 ) Net income Total reclassifications, net of tax $ (6.1 ) $ (6.1 ) Net income KCP&L Details about Accumulated Other Comprehensive Loss Components Amount Reclassified from Accumulated Other Comprehensive Loss Affected Line Item in the Income Statement 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (8.8 ) $ (8.7 ) Interest charges (8.8 ) (8.7 ) Income before income tax expense 3.4 3.4 Income tax benefit Total reclassifications, net of tax $ (5.4 ) $ (5.3 ) Net income

Taxes

Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	22. TAXES Components of income tax expense are detailed in the following tables. Great Plains Energy 2016 2015 2014 Current income taxes (millions) Federal $ 0.3 $ (0.2 ) $ 0.4 State 0.7 (1.1 ) (0.1 ) Total 1.0 (1.3 ) 0.3 Deferred income taxes Federal 140.6 96.9 104.2 State 29.5 28.0 21.6 Total 170.1 124.9 125.8 Noncurrent income taxes Federal — — (2.4 ) State — — (0.5 ) Foreign — — (6.1 ) Total — — (9.0 ) Investment tax credit Deferral 2.5 0.5 — Amortization (1.4 ) (1.4 ) (1.4 ) Total 1.1 (0.9 ) (1.4 ) Income tax expense $ 172.2 $ 122.7 $ 115.7 KCP&L 2016 2015 2014 Current income taxes (millions) Federal $ 24.8 $ (18.7 ) $ (9.4 ) State 4.7 (3.4 ) (2.3 ) Total 29.5 (22.1 ) (11.7 ) Deferred income taxes Federal 76.4 81.9 72.6 State 17.0 17.5 15.8 Total 93.4 99.4 88.4 Investment tax credit Deferral — 0.5 — Amortization (1.0 ) (1.0 ) (1.0 ) Total (1.0 ) (0.5 ) (1.0 ) Income tax expense $ 121.9 $ 76.8 $ 75.7 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 2016 2015 2014 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.1 ) — (0.7 ) Amortization of investment tax credits (0.3 ) (0.4 ) (0.4 ) Federal income tax credits (2.6 ) (4.1 ) (3.8 ) State income taxes 4.2 4.0 3.8 Changes in uncertain tax positions, net — — (1.7 ) Transaction costs 0.9 — — Valuation allowance — 1.5 — Other 0.2 0.5 0.1 Effective income tax rate 37.3 % 36.5 % 32.3 % KCP&L 2016 2015 2014 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.3 ) — (0.9 ) Amortization of investment tax credits (0.3 ) (0.5 ) (0.4 ) Federal income tax credits (3.1 ) (5.6 ) (5.6 ) State income taxes 4.1 4.0 3.7 Valuation allowance — 0.3 — Other (0.2 ) 0.3 — Effective income tax rate 35.2 % 33.5 % 31.8 % 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 2016 2015 2016 2015 Noncurrent deferred income taxes Plant related (2,107.6 ) (1,967.0 ) (1,492.2 ) (1,398.9 ) Income taxes on future regulatory recoveries (148.7 ) (151.3 ) (123.9 ) (125.0 ) Derivative instruments (17.0 ) 20.5 8.5 14.0 Pension and post-retirement benefits 10.5 (0.1 ) 38.6 27.4 SO 2 emission allowance sales 24.1 25.7 24.1 25.7 Fuel recovery mechanisms (22.3 ) (4.5 ) (27.2 ) (6.3 ) Tax credit carryforwards 271.1 256.8 177.4 166.6 Customer demand programs (34.3 ) (22.7 ) (21.8 ) (16.9 ) Solar rebates (27.3 ) (31.9 ) (11.4 ) (13.1 ) Net operating loss carryforward 718.0 734.9 198.3 204.2 Other 20.2 0.7 1.3 (9.6 ) Net noncurrent deferred income tax liability before valuation allowance (1,313.3 ) (1,138.9 ) (1,228.3 ) (1,131.9 ) Valuation allowance (16.4 ) (19.9 ) — (0.7 ) Net noncurrent deferred income tax liability (1,329.7 ) (1,158.8 ) (1,228.3 ) (1,132.6 ) Great Plains Energy KCP&L December 31 2016 2015 2016 2015 (millions) Gross deferred income tax assets $ 1,360.9 $ 1,368.5 $ 747.7 $ 740.9 Gross deferred income tax liabilities (2,690.6 ) (2,527.3 ) (1,976.0 ) (1,873.5 ) Net deferred income tax liability $ (1,329.7 ) $ (1,158.8 ) $ (1,228.3 ) $ (1,132.6 ) Tax Credit Carryforwards At December 31, 2016 and 2015 , Great Plains Energy had $183.5 million and $169.2 million , respectively, of federal general business income tax credit carryforwards. At December 31, 2016 and 2015 , KCP&L had $177.4 million and $166.6 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 2036 . 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, 2016 and 2015 , Great Plains Energy had $87.6 million of federal alternative minimum tax credit carryforwards, all of which was acquired in the GMO acquisition. These credits do not expire and can be used to reduce taxes paid in the future. Net Operating Loss Carryforwards At December 31, 2016 and 2015 , Great Plains Energy had $643.8 million and $656.1 million , respectively, of tax benefits related to federal net operating loss (NOL) carryforwards. Approximately $306.2 million at December 31, 2016 and $313.2 million at December 31, 2015 , respectively, are tax benefits related to NOLs that were acquired in the GMO acquisition. The tax benefits for NOLs originating in 2003 are $23.0 million , $152.4 million originating in 2004, $74.1 million originating in 2005, $53.3 million originating in 2006, $1.3 million originating in 2007, $2.4 million originating in 2008, $36.5 million originating in 2009, $4.1 million originating in 2010, $108.8 million originating in 2011, $2.1 million originating in 2012, $1.4 million originating in 2013, $86.3 million originating in 2014 and $98.1 million originating in 2015. The federal NOL carryforwards expire in years 2023 to 2036 . In addition, Great Plains Energy also had deferred tax benefits of $74.2 million and $78.8 million related to state NOLs as of December 31, 2016 and 2015 , respectively. Of these amounts, approximately $36.1 million and $39.2 million at December 31, 2016 and 2015 , respectively, were acquired in the GMO acquisition. Management does not expect to utilize $16.0 million of NOLs in state tax jurisdictions where the Company does not expect to operate in the future. Therefore, a valuation allowance has been provided against $16.0 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 federal and state tax NOL carryforwards and tax credit carryforwards. During 2016, $3.5 million of tax expense was recorded in continuing operations primarily related to state NOL carryforwards that expired at December 31, 2016.

Segments and Related Informatio

Segments and Related Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segments and Related Information	23 . 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 acquisition of Westar. The summary of significant accounting policies applies to the reportable segment. Segment performance is evaluated based on net income. The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment. 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 2014 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 2,568.2 $ — $ — $ 2,568.2 Depreciation and amortization (306.0 ) — — (306.0 ) Interest charges (183.0 ) (41.2 ) 35.7 (188.5 ) Income tax (expense) benefit (125.6 ) 9.9 — (115.7 ) Net income (loss) 243.5 (0.7 ) — 242.8 Electric Utility Other Eliminations Great Plains Energy 2016 (millions) 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 2014 Assets $ 10,727.7 $ 29.2 $ (303.5 ) $ 10,453.4 Capital expenditures 773.7 — — 773.7

Jointly Owned Electric Utility

Jointly Owned Electric Utility Plants	12 Months Ended
	Dec. 31, 2016
Jointly Owned Electric Utility Plants [Abstract]
Jointly Owned Electric Utility Plants [Text Block]	24. JOINTLY-OWNED ELECTRIC UTILITY PLANTS Great Plains Energy's and KCP&L's share of jointly-owned electric utility plants at December 31, 2016 , 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 $ 1,853.1 $ 1,099.5 $ 670.2 $ 1,334.9 $ 490.6 $ 196.1 Accumulated depreciation 889.6 275.6 261.6 387.3 126.3 80.1 Nuclear fuel, net 62.0 — — — — — Construction work in progress 83.5 30.6 19.9 41.7 22.1 3.7 2017 accredited capacity-MWs 549 699 616 641 NA 172 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 $ 1,853.1 $ 1,099.5 $ 532.8 $ 1,022.4 $ 403.1 Accumulated depreciation 889.6 275.6 210.8 346.6 113.0 Nuclear fuel, net 62.0 — — — — Construction work in progress 83.5 30.6 8.4 23.1 5.0 2017 accredited capacity-MWs 549 699 490 482 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 (Un

Quarterly Operating Results (Unaudited)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	25. QUARTERLY OPERATING RESULTS (UNAUDITED) Quarter Great Plains Energy 1st 2nd 3rd 4th 2016 (millions, except per share amounts) 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 2015 Operating revenue $ 549.1 $ 609.0 $ 781.4 $ 562.7 Operating income 70.1 119.9 256.7 83.4 Net income 18.9 44.4 126.8 22.9 Basic and diluted earnings per common share 0.12 0.28 0.82 0.15 Quarter KCP&L 1st 2nd 3rd 4th 2016 (millions) 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 2015 Operating revenue $ 370.4 $ 417.4 $ 526.3 $ 399.7 Operating income 45.3 79.3 170.8 68.6 Net income 13.2 29.4 84.3 25.9 Quarterly data is subject to seasonal fluctuations with peak periods occurring in the summer months.

Summary of Significant Accoun33

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Organization [Policy Text Block]	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 and a time deposit to be used to fund a portion of the cash consideration for the anticipated acquisition of Westar Energy, Inc. (Westar). 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 electric utility. See Note 23 for additional information.
Use of Estimates, Policy [Policy Text Block]	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, 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 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 time deposit matures in the first quarter of 2017 and the proceeds from this investment are expected to be used to fund a portion of the cash consideration for the anticipated acquisition of Westar. 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, 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. 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. Derivative instruments - The fair value of commodity derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlation among fuel prices, net of estimated credit risk. The fair value of interest rate derivative instruments is determined by calculating the net present value of expected payments and receipts under interest rate swaps using observable market inputs including interest rates and LIBOR swap rates. Management also discounts the value by a contingency factor that it believes is representative of what a market participant would use in valuing these instruments in order to account for the contingent nature of the settlement of these instruments. 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.
Derivatives, Policy [Policy Text Block]	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 used 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. See Note 19 for additional information regarding derivative financial instruments and hedging activities. 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, Policy [Policy Text Block]	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. 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 5.7% in 2016 , 3.0% in 2015 and 5.7% in 2014 . The rates used to compute gross AFUDC for GMO averaged 1.6% in 2016 , 4.2% in 2015 and 6.1% in 2014 . 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 2016 2015 Utility plant, at original cost (millions) Generation (20 - 60 years) $ 8,106.4 $ 7,923.8 Transmission (15 - 70 years) 886.3 848.8 Distribution (8 - 66 years) 3,629.1 3,498.6 General (5 - 50 years) 975.9 918.7 Total (a) $ 13,597.7 $ 13,189.9 (a) Includes $261.2 million and $214.0 million at December 31, 2016 and 2015 , respectively, of land and other assets that are not depreciated. KCP&L December 31 2016 2015 Utility plant, at original cost (millions) Generation (20 - 60 years) $ 6,350.7 $ 6,222.5 Transmission (15 - 70 years) 484.1 465.3 Distribution (8 - 55 years) 2,298.4 2,215.2 General (5 - 50 years) 791.9 737.4 Total (a) $ 9,925.1 $ 9,640.4 (a) Includes $178.0 million and $136.5 million at December 31, 2016 and 2015 , respectively, of land and other assets that are not depreciated.
Depreciation and Amortization, Policy [Policy Text Block]	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 $308.8 million , $299.4 million and $277.9 million for 2016 , 2015 and 2014 , respectively. KCP&L's depreciation expense was $215.4 million , $208.5 million and $189.7 million for 2016 , 2015 and 2014 , respectively.
Nuclear Plant Decommissioning Costs, Policy [Policy Text Block]	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, Policy [Policy Text Block]	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, Policy [Policy Text Block]	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, Policy [Policy Text Block]	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 $70.3 million , $62.0 million and $60.4 million in 2016 , 2015 and 2014 , 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. 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. 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, Policy [Policy Text Block]	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, 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 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. If the fair value of a reporting unit is less than its carrying value including goodwill, an impairment charge for goodwill must be recognized in the financial statements. To measure the amount of the impairment loss to recognize, the implied fair value of the reporting unit goodwill is compared with its carrying value.
Income Taxes, Policy [Policy Text Block]	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. Great Plains Energy and KCP&L have established a net regulatory asset for the additional future revenues to be collected from customers for deferred income taxes. 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, 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 per Common Share Calculation To determine basic earnings per common share (EPS), preferred stock dividend requirements and redemption premium are deducted from net income before dividing by the average number of common shares outstanding. To determine diluted EPS, preferred stock dividend requirements 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. 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.
New Accounting Pronouncements, Policy [Policy Text Block]	New Accounting Standards In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (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. The ASU will replace most existing revenue recognition guidance in GAAP when it becomes effective. 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 Companies plan to adopt ASU No. 2014-09 on January 1, 2018. The standard permits the use of either the retrospective or cumulative effect transition method. The Companies have completed a review of the majority of their revenue arrangements and do not expect the standard to have a material impact on their consolidated financial statements. However, the Companies are still evaluating the impacts on revenue recognition of their remaining revenue arrangements and contracts where collectability is uncertain, as well as the accounting for contributions in aid of construction. The Companies are in the process of determining their method of adoption, which depends in part on completing the evaluation of the remaining items noted above. 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 . The Companies are evaluating the effect that ASU No. 2016-02 will have on their consolidated financial statements and related disclosures and have not yet determined the effect of the standard on their ongoing financial reporting. In March 2016, the FASB issued 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 new guidance is effective for interim and annual periods beginning after December 15, 2016, and early adoption is permitted. This guidance will be applied either prospectively, retrospectively or using a modified retrospective transition method, depending on the area covered in this update. The Companies adopted ASU No. 2016-09 effective January 1, 2017 and it will not have a significant impact on their ongoing financial reporting. In January 2017, the FASB issued ASU No. 2017-04, Simplifying the Test for Goodwill Impairment , which eliminates Step 2 of the goodwill impairment test. Step 2 measures a goodwill impairment loss by computing the implied fair value of a reporting unit's goodwill and comparing it with the carrying amount of that goodwill in the event that the reporting unit does not pass Step 1 of the goodwill impairment test. Under the amendments in this ASU, a goodwill impairment loss would be measured by the amount the carrying value of the reporting unit exceeds its fair value as calculated in Step 1 of the goodwill impairment test. The new guidance is effective for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019, with early adoption permitted for tests performed after January 1, 2017. Great Plains Energy anticipates early adopting ASU No. 2017-04 for its 2017 goodwill impairment test and does not anticipate that it will have a significant impact on its ongoing financial reporting.

Summary of Significant Accoun34

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Schedule of Public Utility Property, Plant, and Equipment [Table Text Block]	Great Plains Energy December 31 2016 2015 Utility plant, at original cost (millions) Generation (20 - 60 years) $ 8,106.4 $ 7,923.8 Transmission (15 - 70 years) 886.3 848.8 Distribution (8 - 66 years) 3,629.1 3,498.6 General (5 - 50 years) 975.9 918.7 Total (a) $ 13,597.7 $ 13,189.9 (a) Includes $261.2 million and $214.0 million at December 31, 2016 and 2015 , respectively, of land and other assets that are not depreciated. KCP&L December 31 2016 2015 Utility plant, at original cost (millions) Generation (20 - 60 years) $ 6,350.7 $ 6,222.5 Transmission (15 - 70 years) 484.1 465.3 Distribution (8 - 55 years) 2,298.4 2,215.2 General (5 - 50 years) 791.9 737.4 Total (a) $ 9,925.1 $ 9,640.4 (a) Includes $178.0 million and $136.5 million at December 31, 2016 and 2015 , respectively, of land and other assets that are not depreciated.
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table reconciles Great Plains Energy's basic and diluted EPS. 2016 2015 2014 (millions, except per share amounts) Income Net income $ 290.0 $ 213.0 $ 242.8 Less: preferred stock dividend requirements and redemption premium 16.5 1.6 1.6 Earnings available for common shareholders $ 273.5 $ 211.4 $ 241.2 Common Shares Outstanding Average number of common shares outstanding 169.4 154.2 153.9 Add: effect of dilutive securities 0.4 0.6 0.2 Diluted average number of common shares outstanding 169.8 154.8 154.1 Basic and Diluted EPS $ 1.61 $ 1.37 $ 1.57
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]	Anti-dilutive shares excluded from the computation of diluted EPS are detailed in the following table. 2016 2015 2014 Assumed conversion of Series B Preferred Stock 7,805,460 — — Performance shares — — 482,987 Restricted stock shares — 900 3,287

Supplemental Cash Flow Inform35

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	Great Plains Energy Other Operating Activities Year Ended December 31 2016 2015 2014 Cash flows affected by changes in: (millions) Receivables $ (18.3 ) $ 12.5 $ 3.0 Accounts receivable pledged as collateral 2.6 (4.0 ) 4.0 Fuel inventories 9.6 (28.3 ) (13.7 ) Materials and supplies (6.5 ) (3.0 ) (0.4 ) Accounts payable (25.4 ) (11.4 ) 15.2 Accrued taxes 8.1 1.1 8.3 Accrued interest 6.1 3.4 (4.1 ) Deferred refueling outage costs (3.1 ) (6.7 ) 17.0 Pension and post-retirement benefit obligations 27.4 18.5 25.5 Allowance for equity funds used during construction (6.6 ) (4.8 ) (18.0 ) Fuel recovery mechanisms (46.9 ) 47.5 (28.5 ) Solar rebates paid (4.5 ) (9.0 ) (43.2 ) Other 15.2 (2.9 ) (12.3 ) Total other operating activities $ (42.3 ) $ 12.9 $ (47.2 ) Cash paid during the period: Interest $ 191.2 $ 182.2 $ 174.8 Income taxes $ 0.1 $ 0.1 $ — Non-cash investing activities: Liabilities accrued for capital expenditures $ 32.4 $ 35.7 $ 57.4 KCP&L Other Operating Activities Year Ended December 31 2016 2015 2014 Cash flows affected by changes in: (millions) Receivables $ (12.4 ) $ 2.6 $ (18.1 ) Fuel inventories 10.6 (24.7 ) (8.5 ) Materials and supplies (4.3 ) (4.5 ) (1.1 ) Accounts payable (30.5 ) (18.0 ) 20.4 Accrued taxes 67.9 (19.0 ) (42.5 ) Accrued interest — 3.4 (0.1 ) Deferred refueling outage costs (3.1 ) (6.7 ) 17.0 Pension and post-retirement benefit obligations 28.6 18.4 26.9 Allowance for equity funds used during construction (6.6 ) (3.8 ) (16.0 ) Fuel recovery mechanisms (53.7 ) 3.5 (2.2 ) Solar rebates paid (3.1 ) (7.2 ) (17.3 ) Other 4.5 (5.5 ) (23.2 ) Total other operating activities $ (2.1 ) $ (61.5 ) $ (64.7 ) Cash paid during the period: Interest $ 127.0 $ 120.2 $ 112.1 Income taxes $ — $ — $ 30.2 Non-cash investing activities: Liabilities accrued for capital expenditures $ 27.2 $ 23.9 $ 48.8

Receivables (Tables)

Receivables (Tables)	12 Months Ended
	Dec. 31, 2016
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 2016 2015 Great Plains Energy (millions) Customer accounts receivable - billed $ 26.2 $ 3.4 Customer accounts receivable - unbilled 79.1 71.6 Allowance for doubtful accounts - customer accounts receivable (4.0 ) (3.8 ) Other receivables 64.7 76.5 Total $ 166.0 $ 147.7 KCP&L Customer accounts receivable - billed $ 25.5 $ 2.8 Customer accounts receivable - unbilled 63.7 58.8 Allowance for doubtful accounts - customer accounts receivable (1.8 ) (1.8 ) Other receivables 51.7 69.4 Total $ 139.1 $ 129.2

Nuclear Plant (Tables)

Nuclear Plant (Tables)	12 Months Ended
	Dec. 31, 2016
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. 2016 2015 Decommissioning Trust (millions) Beginning balance January 1 $ 200.7 $ 199.0 Contributions 3.3 3.3 Earned income, net of fees 4.1 3.4 Net realized gains 0.3 0.7 Net unrealized gains (losses) 14.5 (5.7 ) Ending balance December 31 $ 222.9 $ 200.7
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 2016 2015 Cost Basis Unrealized Gains Unrealized Losses Fair Value Cost Basis Unrealized Gains Unrealized Losses Fair Value (millions) Equity securities $ 93.3 $ 62.1 $ (1.5 ) $ 153.9 $ 89.6 $ 47.9 $ (2.1 ) $ 135.4 Debt securities 63.4 2.3 (0.5 ) 65.2 59.6 2.6 (0.5 ) 61.7 Other 3.8 — — 3.8 3.6 — — 3.6 Total $ 160.5 $ 64.4 $ (2.0 ) $ 222.9 $ 152.8 $ 50.5 $ (2.6 ) $ 200.7
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. 2016 2015 2014 (millions) Realized gains $ 1.6 $ 5.3 $ 1.4 Realized losses (1.3 ) (4.6 ) (1.0 )
Nuclear plant decommissioning costs [Table Text Block]	KCC MPSC (millions) Current cost of decommissioning (in 2014 dollars) Total Station $ 765.1 $ 765.1 KCP&L's 47% Share 359.6 359.6 Future cost of decommissioning (in 2045-2053 dollars) (a) Total Station $ 2,201.5 $ 2,253.1 KCP&L's 47% Share 1,034.7 1,059.0 Annual escalation factor 3.15% 3.22% Annual return on trust assets (b) 6.29% 5.81% (a) Total future cost over an eight year decommissioning period (b) The 6.29% and 5.81% rate of return for KCC and MPSC, respectively, is through 2025. The rates then systematically decrease through 2053 to 0.72% and 2.22% for KCC and MPSC, respectively, based on the assumption that the fund's investment mix will become increasingly conservative as the decommissioning period approaches.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2016
Regulated Operations [Abstract]
Schedule Of Regulatory Assets And Liabilities [Table Text Block]	December 31 2016 2015 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 $ 125.0 $ 26.4 $ 151.4 Loss on reacquired debt 10.0 (a) 1.7 (a) 11.7 11.3 2.2 13.5 Cost of removal 28.6 — 28.6 12.9 — 12.9 Asset retirement obligations 69.6 24.9 94.5 57.9 19.5 77.4 Pension and post-retirement costs 367.9 (b) 104.7 (b) 472.6 358.5 98.9 457.4 Deferred customer programs 45.9 (c) 27.4 (d) 73.3 50.3 20.8 71.1 Fuel recovery mechanism 69.9 (e) — 69.9 16.3 0.1 16.4 Derivative instruments — — — 0.5 6.3 6.8 Iatan No. 1 and common facilities depreciation and carrying costs 13.6 (f) 5.0 (f) 18.6 14.1 5.2 19.3 Iatan No. 2 construction accounting costs 26.9 (g) 16.1 (g) 43.0 28.7 16.0 44.7 Kansas property tax surcharge 3.6 (e) — 3.6 6.8 — 6.8 Solar rebates 29.2 (e) 41.6 (e) 70.8 33.6 49.0 82.6 Transmission delivery charge 3.1 (e) — 3.1 1.7 — 1.7 La Cygne deferred depreciation 2.8 (h) — 2.8 2.9 — 2.9 Other 6.8 (e) — 6.8 11.9 2.3 14.2 Total $ 801.8 $ 246.2 $ 1,048.0 $ 732.4 $ 246.7 $ 979.1 Regulatory Liabilities Emission allowances $ 62.1 $ — $ 62.1 $ 66.1 $ — $ 66.1 Asset retirement obligations 99.7 — 99.7 86.5 — 86.5 Cost of removal — 65.1 (i) 65.1 — 68.2 68.2 Fuel recovery mechanism — 11.6 11.6 — 5.0 5.0 Pension and post-retirement costs 15.3 7.4 22.7 4.8 3.7 8.5 Other 10.3 38.4 48.7 7.2 42.9 50.1 Total $ 187.4 $ 122.5 $ 309.9 $ 164.6 $ 119.8 $ 284.4 (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, $360.7 million and $65.1 million for KCP&L and GMO, respectively, are not included in rate base and are amortized over various periods. (c) $13.2 million not included in rate base and amortized over various periods. (d) $15.4 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 through 2038 . (g) Included in rate base and amortized through 2058 . (h) Included in rate base and amortized through 2040 . (i) Estimated cumulative net provision for future removal costs.

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2016
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, 2016 December 31, 2015 Gross Carrying Amount Accumulated Amortization Gross Carrying Amount Accumulated Amortization Great Plains Energy (millions) Computer software $ 355.2 $ (219.1 ) $ 333.0 $ (191.8 ) Asset improvements 28.8 (6.7 ) 28.3 (6.1 ) KCP&L Computer software $ 338.3 $ (203.1 ) $ 315.5 $ (177.7 ) Asset improvements 13.6 (1.8 ) 13.1 (1.5 )
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. 2016 2015 (millions) Great Plains Energy $ 29.1 $ 28.6 KCP&L 25.7 24.7
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	The following table provides the estimated amortization expense related to Great Plains Energy's and KCP&L's intangible assets for 2017 through 2021 for the intangible assets included in the consolidated balance sheets at December 31, 2016 . 2017 2018 2019 2020 2021 (millions) Great Plains Energy $ 26.1 $ 23.7 $ 21.5 $ 18.0 $ 14.3 KCP&L 24.9 23.2 21.0 17.6 13.9

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2016
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 2016 2015 2016 2015 (millions) Beginning balance $ 275.9 $ 195.9 $ 239.3 $ 177.7 Additions 1.6 54.5 1.3 34.6 Revision in timing and/or estimates 42.1 20.5 40.1 22.2 Settlements (17.4 ) (7.8 ) (15.0 ) (6.7 ) Accretion 13.8 12.8 12.3 11.5 Ending balance $ 316.0 $ 275.9 $ 278.0 $ 239.3

Pension Plans and Other Emplo41

Pension Plans and Other Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Benefit Costs [Table Text Block]	Pension Benefits Other Benefits 2016 2015 2014 2016 2015 2014 Components of net periodic benefit costs (millions) Service cost $ 42.0 $ 45.3 $ 36.7 $ 2.6 $ 3.3 $ 3.7 Interest cost 52.9 50.3 50.1 6.1 6.8 7.9 Expected return on plan assets (49.2 ) (51.7 ) (50.2 ) (3.1 ) (2.9 ) (2.6 ) Prior service cost 0.7 0.8 0.9 1.2 3.1 3.1 Recognized net actuarial (gain) loss 51.8 51.4 50.0 (1.5 ) 0.2 (0.1 ) Transition obligation — — — — 0.2 0.2 Settlement charges — — 8.5 — — — Net periodic benefit costs before regulatory adjustment 98.2 96.1 96.0 5.3 10.7 12.2 Regulatory adjustment (4.9 ) (9.8 ) (11.3 ) 6.0 4.4 4.3 Net periodic benefit costs 93.3 86.3 84.7 11.3 15.1 16.5 Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities Current year net (gain) loss 63.6 8.6 175.8 1.1 (20.6 ) (1.8 ) Amortization of gain (loss) (51.8 ) (51.4 ) (50.0 ) 1.5 (0.2 ) 0.1 Prior service cost — — — (10.2 ) (7.0 ) — Amortization of prior service cost (0.7 ) (0.8 ) (0.9 ) (1.2 ) (3.1 ) (3.1 ) Amortization of transition obligation — — — — (0.2 ) (0.2 ) Other regulatory activity 4.6 4.3 7.3 (5.4 ) (4.4 ) (4.2 ) Total recognized in OCI or regulatory asset/liability 15.7 (39.3 ) 132.2 (14.2 ) (35.5 ) (9.2 ) Total recognized in net periodic benefit costs and OCI or regulatory asset/liability $ 109.0 $ 47.0 $ 216.9 $ (2.9 ) $ (20.4 ) $ 7.3
Schedule of Net Funded Status [Table Text Block]	Pension Benefits Other Benefits 2016 2015 2016 2015 Change in projected benefit obligation (PBO) (millions) PBO at January 1 $ 1,154.8 $ 1,186.8 $ 137.5 $ 165.2 Service cost 42.0 45.3 2.6 3.3 Interest cost 52.9 50.3 6.1 6.8 Contribution by participants — — 5.3 6.9 Amendments — — (10.1 ) (7.1 ) Actuarial (gain) loss 65.5 (59.4 ) 0.6 (23.6 ) Benefits paid (70.6 ) (68.2 ) (11.9 ) (14.0 ) PBO at December 31 $ 1,244.6 $ 1,154.8 $ 130.1 $ 137.5 Change in plan assets Fair value of plan assets at January 1 $ 723.9 $ 730.0 $ 114.3 $ 110.6 Actual return on plan assets 51.1 (16.3 ) 2.6 (0.1 ) Contributions by employer and participants 69.8 76.9 10.2 17.6 Benefits paid (68.0 ) (66.7 ) (11.5 ) (13.8 ) Fair value of plan assets at December 31 $ 776.8 $ 723.9 $ 115.6 $ 114.3 Funded status at December 31 $ (467.8 ) $ (430.9 ) $ (14.5 ) $ (23.2 ) Amounts recognized in the consolidated balance sheets Non-current asset $ — $ — $ 9.0 $ 4.5 Current pension and other post-retirement liability (2.2 ) (2.6 ) (0.8 ) (0.8 ) Noncurrent pension liability and other post-retirement liability (465.6 ) (428.3 ) (22.7 ) (26.9 ) Net amount recognized before regulatory treatment (467.8 ) (430.9 ) (14.5 ) (23.2 ) Accumulated OCI or regulatory asset/liability 476.9 461.2 (23.6 ) (9.4 ) Net amount recognized at December 31 $ 9.1 $ 30.3 $ (38.1 ) $ (32.6 ) Amounts in accumulated OCI or regulatory asset/liability not yet recognized as a component of net periodic benefit cost: Actuarial (gain) loss $ 242.5 $ 230.7 $ (0.7 ) $ (3.3 ) Prior service cost 3.2 3.9 (8.0 ) 3.4 Other 231.2 226.6 (14.9 ) (9.5 ) Net amount recognized at December 31 $ 476.9 $ 461.2 $ (23.6 ) $ (9.4 )
Schedule Of Periodic Benefit Obligation And Accumulated Benefit Obligation And Fair Value Of Plan Assets By Funded And Under Funded Plans [Table Text Block]	2016 2015 Pension plans with the PBO in excess of plan assets (millions) Projected benefit obligation $ 1,244.6 $ 1,154.8 Fair value of plan assets 776.8 723.9 Pension plans with the ABO in excess of plan assets Accumulated benefit obligation $ 1,090.2 $ 1,017.6 Fair value of plan assets 776.8 723.9 Other post-retirement benefit plans with the APBO in excess of plan assets Accumulated other post-retirement benefit obligation $ 61.7 $ 108.5 Fair value of plan assets 38.3 80.8
Schedule of Assumptions Used [Table Text Block]	Weighted-average assumptions used to determine the benefit obligation at December 31 Pension Benefits Other Benefits 2016 2015 2016 2015 Discount rate 4.31 % 4.54 % 4.20 % 4.47 % 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 2016 2015 2016 2015 Discount rate 4.54 % 4.22 % 4.47 % 4.14 % Expected long-term return on plan assets 7.14 % 7.14 % 2.54 % * 2.81 % * Rate of compensation increase 3.62 % 3.62 % 3.50 % 3.50 %
Schedule of Expected Benefit Payments [Table Text Block]	Pension Benefits Other Benefits (millions) 2017 $ 84.9 $ 8.9 2018 81.0 9.4 2019 84.1 10.0 2020 85.9 10.3 2021 87.7 10.7 2022-2026 448.5 58.7
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 $ 0.8 $ (0.7 ) Effect on post-retirement benefit obligation 1.0 (0.8 )
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 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) $ 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 Fair Value Measurements Using Description December 31 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) $ 226.0 $ 195.5 $ — $ — $ 30.5 International (b) 147.4 109.7 — — 37.7 Real estate (c) 45.9 12.2 — — 33.7 Commodities (d) 5.8 — — — 5.8 Fixed income securities Fixed income funds (e) 60.4 20.0 — — 40.4 U.S. Treasury 48.8 48.8 — — — U.S. Agency, state and local obligations 19.0 — 19.0 — — U.S. corporate bonds (f) 108.8 — 108.8 — — Foreign corporate bonds 10.2 — 10.2 — — Hedge funds (g) 23.7 — — — 23.7 Cash equivalents 26.0 26.0 — — — Other 1.9 — 1.9 — — Total $ 723.9 $ 412.2 $ 139.9 $ — $ 171.8 (a) At December 31, 2016 and 2015 , this category is comprised of $128.8 million and $121.6 million , respectively, of traded mutual funds valued at daily listed prices and $84.2 million and $73.9 million , respectively, of traded common stocks and exchange traded funds. At December 31, 2016 and 2015 , this category also includes $34.6 million and $30.5 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, 2016 and 2015 , this category is comprised of $92.8 million and $34.2 million , respectively, of traded mutual funds valued at daily listed prices and $27.6 million and $75.5 million , respectively, of traded American depository receipts, global depository receipts and ordinary shares. At December 31, 2016 and 2015 , this category also includes $43.3 million and $37.7 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, 2016 and 2015, this category is comprised of $12.4 million and $12.2 million , respectively, of traded real estate investment trusts. At December 31, 2016 and 2015 , this category also includes $30.3 million and $33.7 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, 2016 and 2015 , this category is comprised of $20.9 million and $20.0 million , respectively, of traded mutual funds valued at daily listed prices. At December 31, 2016 and 2015 , this category also includes $44.2 million and $40.4 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, 2016 and 2015 , this category is comprised of $115.7 million and $103.0 million , respectively, of corporate bonds, $2.3 million and $2.9 million , respectively, of collateralized mortgage obligations and $2.2 million and $2.9 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 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 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 Fair Value Measurements Using Description December 31 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 $ 3.2 $ 3.2 $ — $ — $ — Fixed income securities Fixed income fund (a) 68.9 0.1 — — 68.8 U.S. Treasury 3.9 3.9 — — — U.S. Agency, state and local obligations 5.4 — 5.4 — — U.S. corporate bonds (b) 15.6 — 15.6 — — Foreign corporate bonds 1.6 — 1.6 — — Cash equivalents 14.0 14.0 — — — Other 1.7 — 1.7 — — Total $ 114.3 $ 21.2 $ 24.3 $ — $ 68.8 (a) At December 31, 2015 , this category is comprised of $0.1 million of traded mutual funds valued at daily listed prices. At December 31, 2016 and 2015 , this category also includes $62.7 million and $68.8 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, 2016 and 2015 , this category is comprised of $14.0 million and $12.6 million , respectively, of corporate bonds, $0.5 million and $0.6 million , respectively, of collateralized mortgage obligations and $3.3 million and $2.4 million , respectively, of other asset-backed securities.

Equity Compensation (Tables)

Equity Compensation (Tables)	12 Months Ended
	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Equity compensation expense and associated income tax benefits	2016 2015 2014 Great Plains Energy (millions) Equity compensation expense $ 5.0 $ 4.0 $ 9.9 Income tax benefit 1.6 1.4 3.6 KCP&L Equity compensation expense $ 3.2 $ 2.6 $ 6.9 Income tax benefit 1.0 0.9 2.4
Performance share activity	Performance Shares Grant Date Fair Value* Beginning balance January 1, 2016 609,010 $ 25.60 Granted 225,204 31.41 Earned (306,953 ) 24.22 Forfeited (1,714 ) 27.61 Performance adjustment 99,553 24.16 Ending balance December 31, 2016 625,100 28.13
Restricted stock activity	Nonvested Restricted Stock Grant Date Fair Value* Beginning balance January 1, 2016 231,508 $ 24.78 Granted and issued 96,053 29.41 Vested (77,317 ) 22.69 Forfeited (572 ) 27.51 Ending balance December 31, 2016 249,672 27.20
Director Deferred Share Units	Share Units Grant Date Fair Value* Beginning balance January 1, 2016 115,415 $ 22.95 Issued 23,172 28.99 Ending balance December 31, 2016 138,587 23.96

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2016
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 2016 2015 KCP&L (millions) General Mortgage Bonds 2.47% EIRR bonds (a) 2017-2035 $ 110.5 $ 110.5 7.15% Series 2009A (8.59% rate) (b) 2019 400.0 400.0 Senior Notes 5.85% Series (5.72% rate) (b) 2017 250.0 250.0 6.375% Series (7.49% rate) (b) 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) (b) 2035 250.0 250.0 5.30% Series 2041 400.0 400.0 EIRR Bonds 0.694% Series 2007A and 2007B (c) 2035 146.5 146.5 2.875% Series 2008 2038 23.4 23.4 Current maturities (281.0 ) — Unamortized discount and debt issuance costs (15.4 ) (17.3 ) Total KCP&L excluding current maturities (d) 2,284.0 2,563.1 Other Great Plains Energy GMO First Mortgage Bonds 9.44% Series 2017-2021 5.7 6.8 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) (b) 2017 100.0 100.0 4.85% Series 2021 350.0 350.0 5.292% Series 2022 287.5 287.5 Current maturities (101.1 ) (1.1 ) Unamortized discount and premium, net and debt issuance costs (1.8 ) (2.1 ) Total Great Plains Energy excluding current maturities (d) $ 3,365.2 $ 3,745.1 (a) Weighted-average interest rates at December 31, 2016 (b) Rate after amortizing gains/losses recognized in other comprehensive income (OCI) on settlements of interest rate hedging instruments (c) Variable rate (d) At December 31, 2016 and 2015, 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. 2016 2015 2014 (millions) KCP&L $ 3.2 $ 3.0 $ 3.0 Other Great Plains Energy 30.6 1.1 1.8 Total Great Plains Energy $ 33.8 $ 4.1 $ 4.8
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. 2017 2018 2019 2020 2021 (millions) Great Plains Energy $ 382.1 $ 351.1 $ 401.1 $ 1.1 $ 432.0 KCP&L 281.0 350.0 400.0 — —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Schedule of Rent Expense [Table Text Block]	2016 2015 2014 (millions) Great Plains Energy $ 15.0 $ 16.8 $ 16.0 KCP&L 13.7 15.0 14.0
Unrecorded Unconditional Purchase Obligations And Lease Commitments [Table Text Block]	Great Plains Energy 2017 2018 2019 2020 2021 After 2021 Total Lease commitments (millions) Operating lease $ 12.9 $ 11.0 $ 9.3 $ 9.7 $ 9.7 $ 110.5 $ 163.1 Capital lease 0.4 0.4 0.4 0.4 0.4 3.1 5.1 Purchase commitments Fuel 259.0 145.8 62.2 53.8 11.2 100.8 632.8 Power 47.3 47.3 47.3 47.3 47.4 462.2 698.8 Other 50.1 32.0 33.3 5.9 6.5 38.7 166.5 Total contractual commitments $ 369.7 $ 236.5 $ 152.5 $ 117.1 $ 75.2 $ 715.3 $ 1,666.3 KCP&L 2017 2018 2019 2020 2021 After 2021 Total Lease commitments (millions) Operating lease $ 12.0 $ 11.0 $ 9.3 $ 9.7 $ 9.7 $ 110.5 $ 162.2 Capital lease 0.2 0.2 0.2 0.2 0.2 1.6 2.6 Purchase commitments Fuel 221.5 119.4 43.6 35.1 1.8 100.8 522.2 Power 34.8 34.8 34.8 34.8 34.9 324.9 499.0 Other 49.3 31.1 30.6 5.0 5.6 33.0 154.6 Total contractual commitments $ 317.8 $ 196.5 $ 118.5 $ 84.8 $ 52.2 $ 570.8 $ 1,340.6
Schedule Of Environmental Capital Expenditures [Table Text Block]	2017 2018 2019 2020 (millions) Great Plains Energy $ 43.4 $ 36.6 $ 11.5 $ 14.0 KCP&L 34.9 16.5 7.6 13.0

Related Party Transactions an45

Related Party Transactions and Relationships (Tables)	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Schedule of related party receivables and payables [Table Text Block]	The following table summarizes KCP&L's related party net receivables. December 31 2016 2015 (millions) Net receivable from GMO $ 64.6 $ 50.0 Net receivable from Great Plains Energy 2.6 15.8

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Values of open positions for derivative instruments [Table Text Block]	The gross notional contract amount and recorded fair values of open positions for derivative instruments are summarized in the following table. The fair values of these derivatives are recorded on the consolidated balance sheets. The fair values below are gross values before netting agreements and netting of cash collateral. December 31 2016 2015 Notional Contract Amount Fair Value Notional Contract Amount Fair Value Great Plains Energy (millions) Non-hedging derivatives Futures contracts $ — $ — $ 26.6 $ (5.7 ) Forward contracts 9.8 2.4 15.6 3.1 Transmission congestion rights 3.7 1.3 5.6 (0.5 ) Interest rate swaps 4,415.0 79.3 — — KCP&L Non-hedging derivatives Futures contracts $ — $ — $ 0.9 $ (0.1 ) Transmission congestion rights 2.7 0.9 4.1 (0.4 )
Fair value of open derivative positions, gross values before netting agreements and netting of cash collateral [Table Text Block]	The fair values of Great Plains Energy's and KCP&L's open derivative positions and balance sheet classification are summarized in the following tables. The fair values below are gross values before netting agreements and netting of cash collateral. Great Plains Energy Balance Sheet Asset Derivatives Liability Derivatives December 31, 2016 Classification Fair Value Fair Value Derivatives Not Designated as Hedging Instruments (millions) Commodity contracts Derivative instruments/Other $ 4.3 $ 0.6 Interest rate contracts Derivative instruments 79.3 — December 31, 2015 Derivatives Not Designated as Hedging Instruments Commodity contracts Other/Derivative instruments $ 3.3 $ 6.4 KCP&L Balance Sheet Asset Derivatives Liability Derivatives December 31, 2016 Classification Fair Value Fair Value Derivatives Not Designated as Hedging Instruments (millions) Commodity contracts Other $ 1.3 $ 0.4 December 31, 2015 Derivatives Not Designated as Hedging Instruments Commodity contracts Other $ 0.2 $ 0.7
Offsetting Derivative Assets and Liabilities [Table Text Block]	The following tables provide information regarding Great Plains Energy's and KCP&L's offsetting of derivative assets and liabilities. Great Plains Energy Gross Amounts Not Offset in the Statement of Financial Position Description Gross Amounts Recognized Gross Amounts Offset in the Statement of Financial Position Net Amounts Presented in the Statement of Financial Position Financial Instruments Cash Collateral Net Amount December 31, 2016 (millions) Derivative assets $ 83.6 $ (0.5 ) $ 83.1 $ — $ — $ 83.1 Derivative liabilities 0.6 (0.5 ) 0.1 — — 0.1 December 31, 2015 Derivative assets $ 3.3 $ (0.2 ) $ 3.1 $ — $ — $ 3.1 Derivative liabilities 6.4 (5.9 ) 0.5 — — 0.5 KCP&L Gross Amounts Not Offset in the Statement of Financial Position Description Gross Amounts Recognized Gross Amounts Offset in the Statement of Financial Position Net Amounts Presented in the Statement of Financial Position Financial Instruments Cash Collateral Net Amount December 31, 2016 (millions) Derivative assets $ 1.3 $ (0.4 ) $ 0.9 $ — $ — $ 0.9 Derivative liabilities 0.4 (0.4 ) — — — — December 31, 2015 Derivative assets $ 0.2 $ (0.2 ) $ — $ — $ — $ — Derivative liabilities 0.7 (0.3 ) 0.4 — — 0.4
Schedule of Other Derivatives Not Designated as Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block]	The following tables summarize the amounts of gain (loss) recognized for the change in fair value of derivatives not designated as hedging instruments for Great Plains Energy and KCP&L. Great Plains Energy Derivatives Not Designated as Hedging Instruments 2016 2015 2014 Location of Gain (Loss) (millions) Electric revenues $ 3.5 $ (8.2 ) $ (14.2 ) Fuel and purchased power (2.7 ) (4.0 ) (3.4 ) Interest charges 79.3 — — Regulatory asset — (6.8 ) (2.7 ) Regulatory liability 1.3 — — Total $ 81.4 $ (19.0 ) $ (20.3 ) KCP&L Derivatives Not Designated as Hedging Instruments 2016 2015 2014 Location of Gain (Loss) (millions) Electric revenues $ 3.5 $ (8.2 ) $ (14.2 ) Fuel and purchased power 0.1 1.5 1.1 Regulatory asset — (0.5 ) (0.2 ) Regulatory liability 1.0 — — Total $ 4.6 $ (7.2 ) $ (13.3 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
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. The fair values below are gross values before netting arrangements and netting of cash collateral. Description December 31 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 — Derivative instruments - commodity (c) 1.3 — — 1.3 Total $ 235.5 $ 192.1 $ 42.1 $ 1.3 Liabilities Derivative instruments - commodity (c) 0.4 — — 0.4 Total $ 0.4 $ — $ — $ 0.4 Other Great Plains Energy Assets Derivative instruments Commodity (c) $ 3.0 $ — $ 2.2 $ 0.8 Interest rate (d) 79.3 — — 79.3 Total $ 82.3 $ — $ 2.2 $ 80.1 Liabilities Derivative instruments - commodity (c) 0.2 — 0.1 0.1 Total $ 0.2 $ — $ 0.1 $ 0.1 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 — Derivative instruments (c)(d) 83.6 — 2.2 81.4 Total $ 317.8 $ 192.1 $ 44.3 $ 81.4 Liabilities Derivative instruments (c) 0.6 — 0.1 0.5 Total $ 0.6 $ — $ 0.1 $ 0.5 Description December 31 Level 1 Level 2 Level 3 KCP&L (millions) Assets Nuclear decommissioning trust (a) Equity securities $ 135.4 $ 135.4 $ — $ — Debt securities U.S. Treasury 26.4 26.4 — — U.S. Agency 1.8 — 1.8 — State and local obligations 4.0 — 4.0 — Corporate bonds 29.2 — 29.2 — Foreign governments 0.3 — 0.3 — Cash equivalents 3.6 3.6 — — Total nuclear decommissioning trust 200.7 165.4 35.3 — Self-insured health plan trust (b) Equity securities 1.1 1.1 — — Debt securities 7.3 — 7.3 — Cash and cash equivalents 5.2 5.2 — — Total self-insured health plan trust 13.6 6.3 7.3 — Derivative instruments - commodity (c) 0.2 — — 0.2 Total $ 214.5 $ 171.7 $ 42.6 $ 0.2 Liabilities Derivative instruments - commodity (c) 0.7 0.1 — 0.6 Total $ 0.7 $ 0.1 $ — $ 0.6 Other Great Plains Energy Assets Derivative instruments - commodity (c) $ 3.1 $ — $ 2.7 $ 0.4 SERP rabbi trusts (e) Equity securities 0.1 0.1 — — Total $ 3.2 $ 0.1 $ 2.7 $ 0.4 Liabilities Derivative instruments - commodity (c) 5.7 5.6 — 0.1 Total $ 5.7 $ 5.6 $ — $ 0.1 Great Plains Energy Assets Nuclear decommissioning trust (a) $ 200.7 $ 165.4 $ 35.3 $ — Self-insured health plan trust (b) 13.6 6.3 7.3 — Derivative instruments (c) 3.3 — 2.7 0.6 SERP rabbi trusts (e) 0.1 0.1 — — Total $ 217.7 $ 171.8 $ 45.3 $ 0.6 Liabilities Derivative instruments (c) 6.4 5.7 — 0.7 Total $ 6.4 $ 5.7 $ — $ 0.7 (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) The fair value of commodity derivative instruments is estimated using market quotes, over-the-counter forward price and volatility curves and correlations among fuel prices, net of estimated credit risk. Derivative instruments classified as Level 1 represent exchange traded derivative instruments. Derivative instruments classified as Level 2 represent non-exchange traded derivative instruments valued using pricing models for which observable market data is available to corroborate the valuation inputs. Derivative instruments classified as Level 3 represent non-exchange traded derivative instruments valued using pricing models for which observable market data is not available to corroborate the valuation inputs and TCRs valued at the most recent auction price in the SPP Integrated Marketplace. (d) 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 LIBOR swap rates. As of December 31, 2016, the calculated net present value was 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 settlement of these instruments. See Note 19 for more details on the interest rate swaps. A decrease in the contingency factor would result in a higher fair value measurement. Management expects that the contingency factor will decrease as the Company obtains certain regulatory approvals connected with the anticipated acquisition of Westar and due to the passage of time. Because of the unobservable nature of the contingency factor, the interest rate derivatives have been classified as Level 3. (e) At December 31, 2016 and 2015, the Supplemental Executive Retirement Plan (SERP) rabbi trusts also included $16.0 million and $16.6 million , respectively, of fixed income funds valued at NAV 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.
Unobservable inputs reconciliation	The following tables reconcile the beginning and ending balances for all Level 3 assets and liabilities measured at fair value on a recurring basis. Great Plains Energy Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative Instruments 2016 2015 (millions) Net asset (liability) at January 1 $ (0.1 ) $ 3.5 Total realized/unrealized gains (losses): included in electric revenue 3.5 (8.2 ) included in fuel and purchased power expense 0.8 (1.5 ) included in non-operating income 11.3 8.6 included in interest charges 79.3 — included in regulatory (asset) liability 1.3 (0.5 ) Purchases 0.3 — Settlements (15.5 ) (2.0 ) Net asset (liability) at December 31 $ 80.9 $ (0.1 ) Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at December 31: included in non-operating income $ 0.1 $ (0.2 ) included in interest charges 79.3 — included in regulatory (asset) liability 1.3 (0.5 ) KCP&L Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative Instruments 2016 2015 (millions) Net asset (liability) at January 1 $ (0.4 ) $ 3.1 Total realized/unrealized gains (losses): included in electric revenue 3.5 (8.2 ) included in regulatory (asset) liability 1.0 (0.4 ) Purchases (0.3 ) (0.8 ) Settlements (2.9 ) 5.9 Net asset (liability) at December 31 $ 0.9 $ (0.4 ) Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at December 31: included in regulatory (asset) liability $ 1.0 $ (0.4 )

Accumulated Other Comprehensi48

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2016
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 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) 2016 Beginning balance January 1 $ (10.1 ) $ (1.9 ) $ (12.0 ) Other comprehensive income (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 5.6 (0.2 ) 5.4 Ending balance December 31 $ (4.5 ) $ (2.1 ) $ (6.6 ) 2015 Beginning balance January 1 $ (15.8 ) $ (2.9 ) $ (18.7 ) Other comprehensive income before reclassifications — 0.6 0.6 Amounts reclassified from accumulated other comprehensive loss 5.7 0.4 6.1 Net current period other comprehensive income 5.7 1.0 6.7 Ending balance December 31 $ (10.1 ) $ (1.9 ) $ (12.0 ) (a) Net of tax KCP&L Gains and Losses on Cash Flow Hedges (a) (millions) 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 ) 2015 Beginning balance January 1 $ (14.9 ) Amounts reclassified from accumulated other comprehensive loss 5.3 Net current period other comprehensive income 5.3 Ending balance December 31 $ (9.6 ) (a) Net of tax
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	The following tables reflect the effect on certain line items of net income from amounts reclassified out of each component of accumulated other comprehensive 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 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (9.2 ) $ (9.2 ) Interest charges (9.2 ) (9.2 ) Income before income tax expense and income from equity investments 3.6 3.5 Income tax benefit $ (5.6 ) $ (5.7 ) Net income Amortization of defined benefit pension items Net losses included in net periodic benefit costs $ (0.8 ) $ (0.7 ) Utility operating and maintenance expenses (0.8 ) (0.7 ) Income before income tax expense and income from equity investments 0.3 0.3 Income tax benefit $ (0.5 ) $ (0.4 ) Net income Total reclassifications, net of tax $ (6.1 ) $ (6.1 ) Net income KCP&L Details about Accumulated Other Comprehensive Loss Components Amount Reclassified from Accumulated Other Comprehensive Loss Affected Line Item in the Income Statement 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (8.8 ) $ (8.7 ) Interest charges (8.8 ) (8.7 ) Income before income tax expense 3.4 3.4 Income tax benefit Total reclassifications, net of tax $ (5.4 ) $ (5.3 ) Net income

Taxes (Tables)

Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Great Plains Energy 2016 2015 2014 Current income taxes (millions) Federal $ 0.3 $ (0.2 ) $ 0.4 State 0.7 (1.1 ) (0.1 ) Total 1.0 (1.3 ) 0.3 Deferred income taxes Federal 140.6 96.9 104.2 State 29.5 28.0 21.6 Total 170.1 124.9 125.8 Noncurrent income taxes Federal — — (2.4 ) State — — (0.5 ) Foreign — — (6.1 ) Total — — (9.0 ) Investment tax credit Deferral 2.5 0.5 — Amortization (1.4 ) (1.4 ) (1.4 ) Total 1.1 (0.9 ) (1.4 ) Income tax expense $ 172.2 $ 122.7 $ 115.7 KCP&L 2016 2015 2014 Current income taxes (millions) Federal $ 24.8 $ (18.7 ) $ (9.4 ) State 4.7 (3.4 ) (2.3 ) Total 29.5 (22.1 ) (11.7 ) Deferred income taxes Federal 76.4 81.9 72.6 State 17.0 17.5 15.8 Total 93.4 99.4 88.4 Investment tax credit Deferral — 0.5 — Amortization (1.0 ) (1.0 ) (1.0 ) Total (1.0 ) (0.5 ) (1.0 ) Income tax expense $ 121.9 $ 76.8 $ 75.7
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	Great Plains Energy 2016 2015 2014 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.1 ) — (0.7 ) Amortization of investment tax credits (0.3 ) (0.4 ) (0.4 ) Federal income tax credits (2.6 ) (4.1 ) (3.8 ) State income taxes 4.2 4.0 3.8 Changes in uncertain tax positions, net — — (1.7 ) Transaction costs 0.9 — — Valuation allowance — 1.5 — Other 0.2 0.5 0.1 Effective income tax rate 37.3 % 36.5 % 32.3 % KCP&L 2016 2015 2014 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.3 ) — (0.9 ) Amortization of investment tax credits (0.3 ) (0.5 ) (0.4 ) Federal income tax credits (3.1 ) (5.6 ) (5.6 ) State income taxes 4.1 4.0 3.7 Valuation allowance — 0.3 — Other (0.2 ) 0.3 — Effective income tax rate 35.2 % 33.5 % 31.8 %
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	Great Plains Energy KCP&L December 31 2016 2015 2016 2015 Noncurrent deferred income taxes Plant related (2,107.6 ) (1,967.0 ) (1,492.2 ) (1,398.9 ) Income taxes on future regulatory recoveries (148.7 ) (151.3 ) (123.9 ) (125.0 ) Derivative instruments (17.0 ) 20.5 8.5 14.0 Pension and post-retirement benefits 10.5 (0.1 ) 38.6 27.4 SO 2 emission allowance sales 24.1 25.7 24.1 25.7 Fuel recovery mechanisms (22.3 ) (4.5 ) (27.2 ) (6.3 ) Tax credit carryforwards 271.1 256.8 177.4 166.6 Customer demand programs (34.3 ) (22.7 ) (21.8 ) (16.9 ) Solar rebates (27.3 ) (31.9 ) (11.4 ) (13.1 ) Net operating loss carryforward 718.0 734.9 198.3 204.2 Other 20.2 0.7 1.3 (9.6 ) Net noncurrent deferred income tax liability before valuation allowance (1,313.3 ) (1,138.9 ) (1,228.3 ) (1,131.9 ) Valuation allowance (16.4 ) (19.9 ) — (0.7 ) Net noncurrent deferred income tax liability (1,329.7 ) (1,158.8 ) (1,228.3 ) (1,132.6 ) Great Plains Energy KCP&L December 31 2016 2015 2016 2015 (millions) Gross deferred income tax assets $ 1,360.9 $ 1,368.5 $ 747.7 $ 740.9 Gross deferred income tax liabilities (2,690.6 ) (2,527.3 ) (1,976.0 ) (1,873.5 ) Net deferred income tax liability $ (1,329.7 ) $ (1,158.8 ) $ (1,228.3 ) $ (1,132.6 )

Segments and Related Informat50

Segments and Related Information (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segment Financial Information [Table Text Block]	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 2014 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 2,568.2 $ — $ — $ 2,568.2 Depreciation and amortization (306.0 ) — — (306.0 ) Interest charges (183.0 ) (41.2 ) 35.7 (188.5 ) Income tax (expense) benefit (125.6 ) 9.9 — (115.7 ) Net income (loss) 243.5 (0.7 ) — 242.8 Electric Utility Other Eliminations Great Plains Energy 2016 (millions) 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 2014 Assets $ 10,727.7 $ 29.2 $ (303.5 ) $ 10,453.4 Capital expenditures 773.7 — — 773.7

Jointly Owned Electric Utilit51

Jointly Owned Electric Utility Plants (Tables)	12 Months Ended
	Dec. 31, 2016
Jointly Owned Electric Utility Plants [Abstract]
Schedule of Jointly Owned Utility Plants [Table Text Block]	Great Plains Energy's and KCP&L's share of jointly-owned electric utility plants at December 31, 2016 , 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 $ 1,853.1 $ 1,099.5 $ 670.2 $ 1,334.9 $ 490.6 $ 196.1 Accumulated depreciation 889.6 275.6 261.6 387.3 126.3 80.1 Nuclear fuel, net 62.0 — — — — — Construction work in progress 83.5 30.6 19.9 41.7 22.1 3.7 2017 accredited capacity-MWs 549 699 616 641 NA 172 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 $ 1,853.1 $ 1,099.5 $ 532.8 $ 1,022.4 $ 403.1 Accumulated depreciation 889.6 275.6 210.8 346.6 113.0 Nuclear fuel, net 62.0 — — — — Construction work in progress 83.5 30.6 8.4 23.1 5.0 2017 accredited capacity-MWs 549 699 490 482 NA

Quarterly Operating Results (52

Quarterly Operating Results (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information [Table Text Block]	Quarter Great Plains Energy 1st 2nd 3rd 4th 2016 (millions, except per share amounts) 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 2015 Operating revenue $ 549.1 $ 609.0 $ 781.4 $ 562.7 Operating income 70.1 119.9 256.7 83.4 Net income 18.9 44.4 126.8 22.9 Basic and diluted earnings per common share 0.12 0.28 0.82 0.15 Quarter KCP&L 1st 2nd 3rd 4th 2016 (millions) 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 2015 Operating revenue $ 370.4 $ 417.4 $ 526.3 $ 399.7 Operating income 45.3 79.3 170.8 68.6 Net income 13.2 29.4 84.3 25.9

Summary of Significant Accoun53

Summary of Significant Accounting Policies Equity Method Investment (Details) - Transource Energy, LLC [Member]	12 Months Ended
	Dec. 31, 2016Rate
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 Accoun54

Summary of Significant Accounting Policies Summary of Significant Accounting Policies Utility Plant (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	$ 308.8	$ 299.4	$ 277.9
Depreciation and amortization	344.8	330.4	306
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Generation or Processing	8,106.4	7,923.8
Public Utilities, Property, Plant and Equipment, Transmission	886.3	848.8
Public Utilities, Property, Plant and Equipment, Distribution	3,629.1	3,498.6
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	975.9	918.7
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 13,597.7	13,189.9
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	$ 261.2	214
Kansas City Power and Light Company [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Depreciation	215.4	208.5	189.7
Depreciation and amortization	$ 247.5	$ 235.7	$ 213.9
Public Utilities, Allowance for Funds Used During Construction, Rate	5.70%	3.00%	5.70%
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Generation or Processing	$ 6,350.7	$ 6,222.5
Public Utilities, Property, Plant and Equipment, Transmission	484.1	465.3
Public Utilities, Property, Plant and Equipment, Distribution	2,298.4	2,215.2
Public Utilities, Property, Plant and Equipment, Other Property, Plant and Equipment	791.9	737.4
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 9,925.1	9,640.4
Kansas City Power and Light Company [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
Kansas City Power and Light Company [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
Kansas City Power and Light Company [Member] | Land and other assets not depreciated [Member]
Utility Plant, at original cost
Public Utilities, Property, Plant and Equipment, Plant in Service	$ 178	$ 136.5
KCPL Greater Missouri Operations [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	1.60%	4.20%	6.10%

Summary of Significant Accoun55

Summary of Significant Accounting Policies Summary of Significant Accounting Policies Revenue Recognition (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Kansas City Power and Light Company [Member] | MISSOURI
Excise and Sales Taxes	$ 70.3	$ 62	$ 60.4

Summary of Significant Accoun56

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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income [Abstract]
Net income									$ 290	$ 213	$ 242.8
Less: preferred stock dividend requirements and redemption premium									16.5	1.6	1.6
Earnings available for common shareholders									$ 273.5	$ 211.4	$ 241.2
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)									169.4	154.2	153.9
Add: effect of dilutive securities (in shares)									0.4	0.6	0.2
Diluted average number of common shares outstanding (in shares)									169.8	154.8	154.1
Earnings Per Share [Abstract]
Basic and Diluted EPS	$ 0.39	$ 0.86	$ 0.20	$ 0.17	$ 0.15	$ 0.82	$ 0.28	$ 0.12	$ 1.61	$ 1.37	$ 1.57
Series B Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage									7.00%	7.00%

Summary of Significant Accoun57

Summary of Significant Accounting Policies Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Performance Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	0	482,987
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	900	3,287
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	0	0

Summary of Significant Accoun58

Summary of Significant Accounting Policies Subsequent Events (Details) - Subsequent Event [Member]	Feb. 28, 2017$ / shares
Kansas City Power and Light Company [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 57,000,000
Dividends Payable, Date to be Paid	Mar. 17, 2017
Dividends Payable, Date Declared, Month and Year	2017-02
Common Stock [Member]
Dividends Declared [Abstract]
Dividends Payable, Amount Per Share	$ 0.275
Dividends Payable, Date to be Paid	Mar. 20, 2017
Dividends Payable, Date of Record	Feb. 27, 2017
Dividends Payable, Date Declared, Month and Year	2017-02
7.00% Mandatory Convertible Preferred Stock, Series B
Dividends Declared [Abstract]
Dividends Payable, Date to be Paid	Mar. 15, 2017
Dividends Payable, Date of Record	Mar. 1, 2017
Dividends Payable, Date Declared, Month and Year	2017-02

Anticipated Acquisition of We59

Anticipated Acquisition of Westar Energy, Inc. (Details) $ / shares in Units, $ in Millions	Oct. 03, 2016USD ($)$ / sharesshares	May 29, 2016USD ($)$ / sharesRateshares	Oct. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2016USD ($)Rateshares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)shares
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Cash consideration to be transferred (per share) | $ / shares		$ 51
Great Plains Energy Average Stock Price - Maximum | $ / shares		33.2283
Great Plains Energy Average Stock Price Minimum | $ / shares		$ 28.5918
Exchange Ratio if Great Plains Energy Avg Stock Price is less than $28.5918		0.3148
Exchange Ratio if Great Plains Energy Avg Stock Price is greater than $33.2283		0.2709
Exchange Ratio Numerator | $ / shares		$ 9
Gross Proceeds from Issuance of Common Stock				$ 1,603.7	$ 3	$ 4.8
Anticipated Acquisition Financing, Mandatory Convertible Preferred Equity				750
Anticipated Acquisition Financing, Common And Preferred Equity				2,350
Anticipated Acquisition Financing, Debt				4,400
Great Plains Energy [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Gross Proceeds from Issuance of Common Stock				1,603.7	$ 3	$ 4.8
Merger Termination Fee, Regulatory Approval				380
Merger Termination Fee Great Plains Energy				180
Westar Energy Inc [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Merger Termination Fee Westar				280
Bridge Loan [Member] | Great Plains Energy [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Amount of bridge facility		$ 8,017		8,017
Amount of bridge facility, as amended				$ 5,100
7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Anticipated Acquisition Of 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%		7.25%
Preferred Stock, Purchase Agreement, Proceeds		$ 750
Depositary Shares [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues | shares	17,300,000		17,300,000
Shares Issued, Price Per Share | $ / shares	$ 50		$ 50
Net Proceeds from Issuance of Depositary Shares	$ 836.2		$ 836.2
Gross Proceeds from Issuance of Depositary Shares	$ 862.5		$ 862.5
Minimum [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Great Plains Energy Average Stock Price - Less Than Maximum, Greater Than Minimum | $ / shares		$ 28.5918
Maximum [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Great Plains Energy Average Stock Price - Less Than Maximum, Greater Than Minimum | $ / shares		$ 33.2283
Common Stock [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues | shares	60,500,000		60,500,000	60,974,205	250,863	258,416
Shares Issued, Price Per Share | $ / shares	$ 26.45		$ 26.45
Net Proceeds from Issuance of Common Stock	$ 1,550		$ 1,550
Gross Proceeds from Issuance of Common Stock	$ 1,600		$ 1,600

Supplemental Cash Flow Inform60

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows affected by changes in:
Receivables	$ (18.3)	$ 12.5	$ 3
Accounts receivable pledged as collateral	2.6	(4)	4
Fuel inventories	9.6	(28.3)	(13.7)
Materials and supplies	(6.5)	(3)	(0.4)
Accounts payable	(25.4)	(11.4)	15.2
Accrued taxes	8.1	1.1	8.3
Accrued interest	6.1	3.4	(4.1)
Deferred refueling outage costs	(3.1)	(6.7)	17
Pension and post-retirement benefit obligations	27.4	18.5	25.5
Allowance for equity funds used during construction	(6.6)	(4.8)	(18)
Fuel recovery mechanisms	(46.9)	47.5	(28.5)
Solar rebates paid	(4.5)	(9)	(43.2)
Other	15.2	(2.9)	(12.3)
Total other operating activities	(42.3)	12.9	(47.2)
Cash paid during the period:
Interest	191.2	182.2	174.8
Income taxes	0.1	0.1	0
Non-cash investing activities:
Liabilities accrued for capital expenditures	32.4	35.7	57.4
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	(12.4)	2.6	(18.1)
Fuel inventories	10.6	(24.7)	(8.5)
Materials and supplies	(4.3)	(4.5)	(1.1)
Accounts payable	(30.5)	(18)	20.4
Accrued taxes	67.9	(19)	(42.5)
Accrued interest	0	3.4	(0.1)
Deferred refueling outage costs	(3.1)	(6.7)	17
Pension and post-retirement benefit obligations	28.6	18.4	26.9
Allowance for equity funds used during construction	(6.6)	(3.8)	(16)
Fuel recovery mechanisms	(53.7)	3.5	(2.2)
Solar rebates paid	(3.1)	(7.2)	(17.3)
Other	4.5	(5.5)	(23.2)
Total other operating activities	(2.1)	(61.5)	(64.7)
Cash paid during the period:
Interest	127	120.2	112.1
Income taxes	0	0	30.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 27.2	$ 23.9	$ 48.8

Receivables Accounts, Notes, an

Receivables Accounts, Notes, and Financing (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 64.7	$ 76.5
Total	166	147.7
Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	51.7	69.4
Total	139.1	129.2
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(4)	(3.8)
Trade Accounts Receivable [Member] | Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(1.8)	(1.8)
Trade Accounts Receivable [Member] | Billed Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	26.2	3.4
Trade Accounts Receivable [Member] | Billed Revenues [Member] | Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	25.5	2.8
Trade Accounts Receivable [Member] | Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	79.1	71.6
Trade Accounts Receivable [Member] | Unbilled Revenues [Member] | Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	$ 63.7	$ 58.8

Receivables Narrative (Details)

Receivables Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	$ 172.4	$ 175
Collateralized note payable	172.4	175
Kansas City Power and Light Company [Member]
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	110	110
Collateralized note payable	110	$ 110
Maximum amount of outstanding principal under receivables agreement	110
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	65
Maximum amount of outstanding principal under receivables agreement from mid-June to mid-November	$ 80

Nuclear Plant (Details)

Nuclear Plant (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments in decommissioning trust fund [Line Items]
Cost Basis	$ 160.5	$ 152.8
Unrealized Gains	64.4	50.5
Unrealized Losses	(2)	(2.6)
Fair Value	$ 222.9	200.7	$ 199
Weighted average maturity of debt securities (in years)	8 years
Realized gains	$ 1.6	5.3	1.4
Realized losses	(1.3)	(4.6)	$ (1)
Equity Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	93.3	89.6
Unrealized Gains	62.1	47.9
Unrealized Losses	(1.5)	(2.1)
Fair Value	153.9	135.4
Debt Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	63.4	59.6
Unrealized Gains	2.3	2.6
Unrealized Losses	(0.5)	(0.5)
Fair Value	65.2	61.7
Other Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	3.8	3.6
Fair Value	$ 3.8	$ 3.6

Nuclear Plant Decommissioning T

Nuclear Plant Decommissioning Trust (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	$ 200.7	$ 199
Contributions	3.3	3.3
Earned income, net of fees	4.1	3.4
Net realized gains	0.3	0.7
Net unrealized gains (losses)	14.5	(5.7)
Ending balance December 31	$ 222.9	200.7
Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%
Nuclear Insurance [Abstract]
Industry aggregate limit on nuclear insurance for property claims including accidental damages	$ 3,200
Industry aggregate limit on non-nuclear acts of terrorism	1,800
Amount of insurance against public liability claims resulting from nuclear incidents to full limit of public liability	13,400
Maximum available commercial insurance	400
Remaining balance provided through industry wide retrospective assesment program mandated by law	13,000
Maximum amount able to be assessed to owners	127.3
SFP Program-annual amount payable per incident	19
Amount of decontamination liability, premature decommissioning liability and property damage insurance	2,800
Premature decommissioning coverage applies only if property damage exceeds this amount and trust funds have been exhausted	500
Estimated maximum amount of retrospective assessments under the current policies	37.5
Wolf Creek [Member] | Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	765.1
Future cost of decommissioning (in 2045 through 2053 dollars)	$ 2,253.1
Annual Escalation Factor	3.22%
Annual return on trust assets through 2025	5.81%
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 2014 dollars)	$ 765.1
Future cost of decommissioning (in 2045 through 2053 dollars)	$ 2,201.5
Annual Escalation Factor	3.15%
Annual return on trust assets through 2025	6.29%
Annual return on trusts assets in 2053	0.72%
Kansas City Power and Light Company [Member]
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	$ 200.7	199
Contributions	3.3	3.3
Earned income, net of fees	4.1	3.4
Net realized gains	0.3	0.7
Net unrealized gains (losses)	14.5	(5.7)
Ending balance December 31	$ 222.9	$ 200.7
Kansas City Power and Light Company [Member] | Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage in Wolf Creek, a nuclear generating unit (in hundredths)	47.00%
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
Estimated maximum amount of retrospective assessments under the current policies	17.6
Kansas City Power and Light Company [Member] | Wolf Creek [Member] | Missouri Public Service Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	359.6
Future cost of decommissioning (in 2045 through 2053 dollars)	1,059
Kansas City Power and Light Company [Member] | Wolf Creek [Member] | Kansas Corporation Commission [Member]
Nuclear Plant Decommissioning Costs [Abstract]
Current cost of decommissioning (in 2014 dollars)	359.6
Future cost of decommissioning (in 2045 through 2053 dollars)	$ 1,034.7

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2016	Sep. 30, 2016	Jul. 31, 2016	Feb. 29, 2016
Kansas City Power and Light Company [Member] | 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, requested, not including rebasing fuel and purchased power expense			$ 62.9
Return on equity, requested (in hundredths)			9.90%
Rate-making equity ratio, requested (in hundredths)			49.88%
Commission Staff Recommended Return On Equity Percentage	8.65%
Kansas City Power and Light Company [Member] | Kansas Corporation Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue increase, requested	$ 2.8
KCPL Greater Missouri Operations [Member] | Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue increase, requested				$ 59.3
Return on equity, requested (in hundredths)				9.90%
Rate-making equity ratio, requested (in hundredths)				54.83%
Annual revenue increase authorized		$ 3
Maximum [Member] | Kansas City Power and Light Company [Member] | Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Commission Staff Recommended Return On Equity Percentage	8.75%
Maximum [Member] | KCPL Greater Missouri Operations [Member] | Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Return on equity, approved (in hundredths)		9.75%
Minimum [Member] | Kansas City Power and Light Company [Member] | Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Commission Staff Recommended Return On Equity Percentage	7.90%
Minimum [Member] | KCPL Greater Missouri Operations [Member] | Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Return on equity, approved (in hundredths)		9.50%

Regulatory Matters Asset (Detai

Regulatory Matters Asset (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 1,048	$ 979.1
Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	148.7	151.4
Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	11.7	13.5
Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	28.6	12.9
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	94.5	77.4
Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	472.6	457.4
Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	73.3	71.1
Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	69.9	16.4
Derivative instruments [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0	6.8
Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	18.6	19.3
Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	43	44.7
Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	3.6	6.8
Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	70.8	82.6
Transmission Delivery Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	3.1	1.7
LaCygne Deferred Depreciation [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	2.8	2.9
Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	6.8	14.2
Kansas City Power and Light Company [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	801.8	732.4
Kansas City Power and Light Company [Member] | Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	123.9	125
Kansas City Power and Light Company [Member] | Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	10	11.3
Kansas City Power and Light Company [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	28.6	12.9
Kansas City Power and Light Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	69.6	57.9
Kansas City Power and Light Company [Member] | Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	367.9	358.5
Amount not included in rate base	360.7
Kansas City Power and Light Company [Member] | Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	45.9	50.3
Amount not included in rate base	13.2
Kansas City Power and Light Company [Member] | Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	69.9	16.3
Kansas City Power and Light Company [Member] | Derivative instruments [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0	0.5
Kansas City Power and Light Company [Member] | Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 13.6	14.1
Regulatory Noncurrent Asset, End Date for Recovery	Dec. 31, 2038
Kansas City Power and Light Company [Member] | Iatan No. 2 construction accounting costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 26.9	28.7
Regulatory Noncurrent Asset, End Date for Recovery	Dec. 31, 2058
Kansas City Power and Light Company [Member] | Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 3.6	6.8
Kansas City Power and Light Company [Member] | Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	29.2	33.6
Kansas City Power and Light Company [Member] | Transmission Delivery Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	3.1	1.7
Kansas City Power and Light Company [Member] | LaCygne Deferred Depreciation [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 2.8	2.9
Regulatory Noncurrent Asset, End Date for Recovery	Dec. 31, 2040
Kansas City Power and Light Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 6.8	11.9
KCPL Greater Missouri Operations [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	246.2	246.7
KCPL Greater Missouri Operations [Member] | Taxes recoverable through future rates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	24.8	26.4
KCPL Greater Missouri Operations [Member] | Loss on reacquired debt [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	1.7	2.2
KCPL Greater Missouri Operations [Member] | Removal Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0	0
KCPL Greater Missouri Operations [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	24.9	19.5
KCPL Greater Missouri Operations [Member] | Pension and post-retirement costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	104.7	98.9
Amount not included in rate base	65.1
KCPL Greater Missouri Operations [Member] | Deferred customer programs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	27.4	20.8
Amount not included in rate base	15.4
KCPL Greater Missouri Operations [Member] | Fuel recovery mechanisms [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0	0.1
KCPL Greater Missouri Operations [Member] | Derivative instruments [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0	6.3
KCPL Greater Missouri Operations [Member] | Iatan No. 1 and Common facilities depreciation and carrying costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 5	5.2
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	$ 16.1	16
Regulatory Noncurrent Asset, End Date for Recovery	Dec. 31, 2058
KCPL Greater Missouri Operations [Member] | Kansas property tax surcharge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 0	0
KCPL Greater Missouri Operations [Member] | Solar Rebates [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	41.6	49
KCPL Greater Missouri Operations [Member] | Transmission Delivery Charge [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0	0
KCPL Greater Missouri Operations [Member] | LaCygne Deferred Depreciation [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	0	0
KCPL Greater Missouri Operations [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 0	$ 2.3

Regulatory Matters Liabilities

Regulatory Matters Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 309.9	$ 284.4
Emission allowances [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	62.1	66.1
Asset retirement obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	99.7	86.5
Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	65.1	68.2
Deferred Fuel Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	11.6	5
Pension [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	22.7	8.5
Other Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	48.7	50.1
Kansas City Power and Light Company [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	187.4	164.6
Kansas City Power and Light Company [Member] | Emission allowances [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	62.1	66.1
Kansas City Power and Light Company [Member] | Asset retirement obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	99.7	86.5
Kansas City Power and Light Company [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Kansas City Power and Light Company [Member] | Deferred Fuel Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Kansas City Power and Light Company [Member] | Pension [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	15.3	4.8
Kansas City Power and Light Company [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	10.3	7.2
KCPL Greater Missouri Operations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	122.5	119.8
KCPL Greater Missouri Operations [Member] | Emission allowances [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
KCPL Greater Missouri Operations [Member] | Asset retirement obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
KCPL Greater Missouri Operations [Member] | Removal Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	65.1	68.2
KCPL Greater Missouri Operations [Member] | Deferred Fuel Costs [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	11.6	5
KCPL Greater Missouri Operations [Member] | Pension [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	7.4	3.7
KCPL Greater Missouri Operations [Member] | Other Regulatory Assets (Liabilities) [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 38.4	$ 42.9

Goodwill and Intangible Asset68

Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 169	$ 169

Intangibles Assets (Details)

Intangibles Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 29.1	$ 28.6
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	26.1
Finite-Lived Intangible Assets, Amortization Expense, Year Two	23.7
Finite-Lived Intangible Assets, Amortization Expense, Year Three	21.5
Finite-Lived Intangible Assets, Amortization Expense, Year Four	18
Finite-Lived Intangible Assets, Amortization Expense, Year Five	14.3
Kansas City Power and Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets	25.7	24.7
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	24.9
Finite-Lived Intangible Assets, Amortization Expense, Year Two	23.2
Finite-Lived Intangible Assets, Amortization Expense, Year Three	21
Finite-Lived Intangible Assets, Amortization Expense, Year Four	17.6
Finite-Lived Intangible Assets, Amortization Expense, Year Five	13.9
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	355.2	333
Finite-Lived Intangible Assets, Accumulated Amortization	(219.1)	(191.8)
Computer Software, Intangible Asset [Member] | Kansas City Power and Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	338.3	315.5
Finite-Lived Intangible Assets, Accumulated Amortization	(203.1)	(177.7)
Asset Improvements [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	28.8	28.3
Finite-Lived Intangible Assets, Accumulated Amortization	(6.7)	(6.1)
Asset Improvements [Member] | Kansas City Power and Light Company [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	13.6	13.1
Finite-Lived Intangible Assets, Accumulated Amortization	$ (1.8)	$ (1.5)

Asset Retirement Obligations (D

Asset Retirement Obligations (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2016	Dec. 31, 2015
Increase in asset retirement obligations due to CCR regulations	$ 69.5
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance		$ 275.9	$ 195.9
Additions		1.6	54.5
Revision in timing and/or estimates		42.1	20.5
Settlements		(17.4)	(7.8)
Accretion		13.8	12.8
Asset Retirement Obligation, Ending Balance		$ 316	275.9
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.
Kansas City Power and Light Company [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	$ 51.3
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance		$ 239.3	177.7
Additions		1.3	34.6
Revision in timing and/or estimates		40.1	22.2
Settlements		(15)	(6.7)
Accretion		12.3	11.5
Asset Retirement Obligation, Ending Balance		$ 278	$ 239.3
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.
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.

Pension Plans and Other Emplo71

Pension Plans and Other Employee Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Amounts recognized in the consolidated balance sheets [Abstract]
Current pension and other post-retirement liability	$ (3)	$ (3.4)
Noncurrent pension liability and other post-retirement liability	(488.3)	(455.2)
Pension plans with the accumulated benefit obligation in excess of plans assets [Abstract]
Unfunded accumulated benefit obligation for GMO SERP	23.6
Segregated assets for GMO SERP	15.8
Employee Savings Plans [Abstract]
Defined contribution savings plan, cost of plan	11.5	10.6	$ 9.7
Kansas City Power and Light Company [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Current pension and other post-retirement liability	(1.6)	(2)
Noncurrent pension liability and other post-retirement liability	(465.8)	(433.4)
Employee Savings Plans [Abstract]
Defined contribution savings plan, cost of plan	8	7.9	7.1
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	1,154.8	1,186.8
Service cost	42	45.3	36.7
Interest cost	52.9	50.3	50.1
Contributions by participants	0	0
Amendments	0	0
Actuarial (gain) loss	65.5	(59.4)
Benefits Paid	(70.6)	(68.2)
Defined Benefit Plan, Benefit Obligation	1,244.6	1,154.8	1,186.8
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of the year	723.9	730
Actual return on plan assets	51.1	(16.3)
Contributions by employer and participants	69.8	76.9
Benefits paid	(68)	(66.7)
Fair value of plan assets at end of the year	776.8	723.9	730
Funded status at end of year	(467.8)	(430.9)
Amounts recognized in the consolidated balance sheets [Abstract]
Non-current asset	0	0
Current pension and other post-retirement liability	(2.2)	(2.6)
Noncurrent pension liability and other post-retirement liability	(465.6)	(428.3)
Net amount recognized before regulatory treatment	(467.8)	(430.9)
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or Regulatory Asset Liability	476.9	461.2
Defined Benefit Plan, Amounts Recognized in Balance Sheet	9.1	30.3
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	230.7
Prior service cost	3.2	3.9
Other	231.2	226.6
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or Regulatory Asset Liability	476.9	461.2
Components of net periodic benefit costs [Abstract]
Service cost	42	45.3	36.7
Interest cost	52.9	50.3	50.1
Expected return on plan assets	(49.2)	(51.7)	(50.2)
Prior service cost	0.7	0.8	0.9
Recognized net actuarial (gain)/loss	51.8	51.4	50
Transition obligation	0	0	0
Settlement charges	0	0	8.5
Net periodic benefit costs before regulatory adjustment	98.2	96.1	96
Regulatory adjustment	(4.9)	(9.8)	(11.3)
Net periodic benefit costs	93.3	86.3	84.7
Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income Regulatory Assets/Liabilities [Abstract]
Current year net (gain) loss	63.6	8.6	175.8
Amortization of gain (loss)	(51.8)	(51.4)	(50)
Prior service cost	0	0	0
Amortization of prior service cost	(0.7)	(0.8)	(0.9)
Amortization of transition obligation	0	0	0
Other regulatory activity	4.6	4.3	7.3
Total Recognized In Other Comprehensive Income Or Regulatory Asset/Liability	15.7	(39.3)	132.2
Total Recognized In Net Periodic Benefit Costs And Other Comprehensive Income Or Regulatory Asset/Liability	109	47	216.9
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	$ 49.7
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	1,017.6
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation	1,244.6	1,154.8
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	776.8	723.9
Pension plans with the accumulated benefit obligation in excess of plans assets [Abstract]
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation	1,090.2	1,017.6
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	$ 776.8	$ 723.9
Weighted average assumptions used to determine the benefit obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.31%	4.54%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	3.62%	3.62%
Defined Benefit Plan, Assumptions Used in Calculations, Narrative 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	4.54%	4.22%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.14%	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	$ 79.6
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	84.9
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	81
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	84.1
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	85.9
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	87.7
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	$ 448.5
Defined Benefit Plan, Target Allocation Percentage	The portfolios are invested, and periodically rebalanced, to achieve targeted allocations of approximately 34% U.S. large cap and small cap equity securities, 21% international equity securities, 36% fixed income securities, 6% 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	$ 137.5	$ 165.2
Service cost	2.6	3.3	3.7
Interest cost	6.1	6.8	7.9
Contributions by participants	5.3	6.9
Amendments	(10.1)	(7.1)
Actuarial (gain) loss	0.6	(23.6)
Benefits Paid	(11.9)	(14)
Defined Benefit Plan, Benefit Obligation	130.1	137.5	165.2
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of the year	114.3	110.6
Actual return on plan assets	2.6	(0.1)
Contributions by employer and participants	10.2	17.6
Benefits paid	(11.5)	(13.8)
Fair value of plan assets at end of the year	115.6	114.3	110.6
Funded status at end of year	(14.5)	(23.2)
Amounts recognized in the consolidated balance sheets [Abstract]
Non-current asset	9	4.5
Current pension and other post-retirement liability	(0.8)	(0.8)
Noncurrent pension liability and other post-retirement liability	(22.7)	(26.9)
Net amount recognized before regulatory treatment	(14.5)	(23.2)
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or Regulatory Asset Liability	(23.6)	(9.4)
Defined Benefit Plan, Amounts Recognized in Balance Sheet	(38.1)	(32.6)
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)	(3.3)
Prior service cost	(8)	3.4
Other	(14.9)	(9.5)
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or Regulatory Asset Liability	(23.6)	(9.4)
Components of net periodic benefit costs [Abstract]
Service cost	2.6	3.3	3.7
Interest cost	6.1	6.8	7.9
Expected return on plan assets	(3.1)	(2.9)	(2.6)
Prior service cost	1.2	3.1	3.1
Recognized net actuarial (gain)/loss	(1.5)	0.2	(0.1)
Transition obligation	0	0.2	0.2
Settlement charges	0	0	0
Net periodic benefit costs before regulatory adjustment	5.3	10.7	12.2
Regulatory adjustment	6	4.4	4.3
Net periodic benefit costs	11.3	15.1	16.5
Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income Regulatory Assets/Liabilities [Abstract]
Current year net (gain) loss	1.1	(20.6)	(1.8)
Amortization of gain (loss)	1.5	(0.2)	0.1
Prior service cost	(10.2)	(7)	0
Amortization of prior service cost	(1.2)	(3.1)	(3.1)
Amortization of transition obligation	0	(0.2)	(0.2)
Other regulatory activity	(5.4)	(4.4)	(4.2)
Total Recognized In Other Comprehensive Income Or Regulatory Asset/Liability	(14.2)	(35.5)	(9.2)
Total Recognized In Net Periodic Benefit Costs And Other Comprehensive Income Or Regulatory Asset/Liability	(2.9)	(20.4)	$ 7.3
Net (gain) loss for the defined benefit plans that will be amortized in the next fiscal year	(0.5)
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation	61.7	108.5
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	$ 38.3	$ 80.8
Weighted average assumptions used to determine the benefit obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.20%	4.47%
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	4.47%	4.14%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	2.54%	2.81%
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 Payments, Next Twelve Months	8.9
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	9.4
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	10
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	10.3
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	10.7
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	$ 58.7
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)	6.50%	6.80%
Health care cost rate declining through	2,025
Ultimate cost trend rate (in hundredths)	4.50%	4.50%
Effect on total service and interest component, increase	$ 0.8
Effect on total service and interest component, decrease	(0.7)
Effect on post-retirement benefit obligation, increase	1
Effect on post-retirement benefit obligation, decrease	$ (0.8)
Wolf Creek [Member]
Defined Benefit Plan Disclosure [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	47.00%
Wolf Creek [Member] | Kansas City Power and Light Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	47.00%

Pension Plans and Other Emplo72

Pension Plans and Other Employee Benefits Pension Plans Fair Value (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	$ 776,800,000	$ 723,900,000	$ 730,000,000
Alternative Investments, Fair Value Disclosure	182,100,000	171,800,000
Pension Plans, Defined Benefit [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	42,700,000	45,900,000
Alternative Investments, Fair Value Disclosure	30,300,000	33,700,000
Pension Plans, Defined Benefit [Member] | Real Estate [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investments, Fair Value Disclosure	30,300,000	33,700,000
Pension Plans, Defined Benefit [Member] | Real Estate [Member] | Real Estate Investment Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	12,400,000	12,200,000
Pension Plans, Defined Benefit [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	15,600,000	23,700,000
Alternative Investments, Fair Value Disclosure	15,600,000	23,700,000
Pension Plans, Defined Benefit [Member] | US Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	247,600,000	226,000,000
Alternative Investments, Fair Value Disclosure	34,600,000	30,500,000
Pension Plans, Defined Benefit [Member] | US Equity Securities [Member] | Traded Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	128,800,000	121,600,000
Pension Plans, Defined Benefit [Member] | US Equity Securities [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investments, Fair Value Disclosure	34,600,000	30,500,000
Pension Plans, Defined Benefit [Member] | US Equity Securities [Member] | Common Stock and Exchange Traded Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	84,200,000	73,900,000
Pension Plans, Defined Benefit [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	163,700,000	147,400,000
Alternative Investments, Fair Value Disclosure	43,300,000	37,700,000
Pension Plans, Defined Benefit [Member] | International Equity Securities [Member] | Traded Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	92,800,000	34,200,000
Pension Plans, Defined Benefit [Member] | International Equity Securities [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investments, Fair Value Disclosure	43,300,000	37,700,000
Pension Plans, Defined Benefit [Member] | International Equity Securities [Member] | American Depository Receipts Global Depository Receipts and Ordinary Shares [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	27,600,000	75,500,000
Pension Plans, Defined Benefit [Member] | Commodity Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	14,100,000	5,800,000
Alternative Investments, Fair Value Disclosure	14,100,000	5,800,000
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	65,100,000	60,400,000
Alternative Investments, Fair Value Disclosure	44,200,000	40,400,000
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Traded Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	20,900,000	20,000,000
Pension Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investments, Fair Value Disclosure	44,200,000	40,400,000
Pension Plans, Defined Benefit [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	52,200,000	48,800,000
Alternative Investments, Fair Value Disclosure	0	0
Pension Plans, Defined Benefit [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	17,900,000	19,000,000
Alternative Investments, Fair Value Disclosure	0	0
Pension Plans, Defined Benefit [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	120,200,000	108,800,000
Alternative Investments, Fair Value Disclosure	0	0
Pension Plans, Defined Benefit [Member] | US corporate bonds [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	115,700,000	103,000,000
Pension Plans, Defined Benefit [Member] | US corporate bonds [Member] | Collateralized Mortgage Obligation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	2,300,000	2,900,000
Pension Plans, Defined Benefit [Member] | US corporate bonds [Member] | Asset-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	2,200,000	2,900,000
Pension Plans, Defined Benefit [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	9,300,000	10,200,000
Alternative Investments, Fair Value Disclosure	0	0
Pension Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	31,700,000	26,000,000
Alternative Investments, Fair Value Disclosure	0	0
Pension Plans, Defined Benefit [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	(3,300,000)	1,900,000
Alternative Investments, Fair Value Disclosure	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	450,600,000	412,200,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	12,400,000	12,200,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	213,000,000	195,500,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	120,400,000	109,700,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Commodity Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	20,900,000	20,000,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	52,200,000	48,800,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	31,700,000	26,000,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	144,100,000	139,900,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Commodity Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	17,900,000	19,000,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	120,200,000	108,800,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	9,300,000	10,200,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	(3,300,000)	1,900,000
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | International Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Pension Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	115,600,000	114,300,000	$ 110,600,000
Alternative Investments, Fair Value Disclosure	62,700,000	68,800,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	4,100,000	3,200,000
Alternative Investments, Fair Value Disclosure	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	62,700,000	68,900,000
Alternative Investments, Fair Value Disclosure	62,700,000	68,800,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Traded Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets		100,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income Funds [Member] | Institutional Common Collective Trust Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Alternative Investments, Fair Value Disclosure	62,700,000	68,800,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	3,900,000	3,900,000
Alternative Investments, Fair Value Disclosure	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	4,300,000	5,400,000
Alternative Investments, Fair Value Disclosure	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	17,800,000	15,600,000
Alternative Investments, Fair Value Disclosure	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | US corporate bonds [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	14,000,000	12,600,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | US corporate bonds [Member] | Collateralized Mortgage Obligation Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	500,000	600,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | US corporate bonds [Member] | Asset-backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	3,300,000	2,400,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	1,600,000	1,600,000
Alternative Investments, Fair Value Disclosure	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	19,500,000	14,000,000
Alternative Investments, Fair Value Disclosure	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	1,700,000	1,700,000
Alternative Investments, Fair Value Disclosure	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	27,700,000	21,200,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	4,100,000	3,200,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	100,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	3,900,000	3,900,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	19,500,000	14,000,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	200,000	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	25,200,000	24,300,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	4,300,000	5,400,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	17,800,000	15,600,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	1,600,000	1,600,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	1,500,000	1,700,000
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US Agency, State and Political Subdivisions Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | US corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Other Plan Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Plan Assets	$ 0	$ 0

Equity Compensation (Details)

Equity Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	$ 5	$ 4	$ 9.9
Income tax benefit	$ 1.6	$ 1.4	$ 3.6
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)	3.61%
Risk-free interest rate (in hundredths)	0.94%
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)	609,010
Granted (in shares)	225,204
Earned (in shares)	(306,953)
Forfeited (in shares)	(1,714)
Performance adjustment (in shares)	99,553
Ending balance (in shares)	625,100	609,010
Weighted average beginning balance (in dollars per share)	$ 25.60
Weighted average granted (in dollars per share)	31.41	$ 24.03	$ 28.78
Weighted average earned (in dollars per share)	24.22
Weighted average forfeited (in dollars per share)	27.61
Weighted average performance adjustment (in dollars per share)	24.16
Weighted average ending balance (in dollars per share)	$ 28.13	$ 25.60
Total unrecognized compensation expense	$ 6.4
Remaining weighted-average contractual term (in years)	1 year 1 month
Fair value of performance shares earned and paid	$ 7.4	$ 0.5	$ 2.8
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)	231,508
Granted (in shares)	96,053
Vested (in shares)	(77,317)
Forfeited (in shares)	(572)
Ending balance (in shares)	249,672	231,508
Weighted average beginning balance (in dollars per share)	$ 24.78
Weighted average granted (in dollars per share)	29.41	$ 25.89	$ 25.70
Weighted average vested (in dollars per share)	22.69
Weighted average forfeited (in dollars per share)	27.51
Weighted average ending balance (in dollars per share)	$ 27.20	$ 24.78
Total unrecognized compensation expense	$ 2.6
Total fair value of shares vested	$ 1.8	$ 2.2	$ 1.9
Remaining weighted-average contractual term (in years)	1 year 2 months
Kansas City Power and Light Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 3.2	2.6	6.9
Income tax benefit	$ 1	$ 0.9	$ 2.4

Equity Compensation Equity Comp

Equity Compensation Equity Compensation Deferred Directors (Details) - Director [Member] - Director Deferred Share Units [Member]	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Director deferred share units [Roll Forward]
Director deferred share units, beginning balance (in shares) | shares	115,415
Director deferred share units, issued (in shares) | shares	23,172
Director deferred share units, ending balance (in shares) | shares	138,587
Weighted-average grant date fair value, director deferred share units, beginning balance (in dollars per share) | $ / shares	$ 22.95
Weighted-average grant date fair value, director deferred share units, issued (in dollars per share) | $ / shares	28.99
Weighted-average grant date fair value, director deferred share units, ending balance (in dollars per share) | $ / shares	$ 23.96

Short-term Borrowings and Sho75

Short-term Borrowings and Short-term Bank Lines of Credit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	May 29, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Amount of outstanding cash borrowings	$ 0		$ 10
Commercial paper outstanding	334.8		224
Great Plains Energy [Member]
Short-term Debt [Line Items]
Amount of outstanding cash borrowings	0		10
Great Plains Energy [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200
Revolving credit facility expiration date	Oct. 31, 2019
Maximum borrowing capacity with transfer of unused commitments	$ 400
Line of Credit Facility, Covenant Terms	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. In June 2016, the facility was amended to increase the maximum consolidated indebtedness to consolidate capitalization ratio of 0.65 to 1.00 to a level such that, if Great Plains Energy would not be in compliance with the covenant as of the date of the closing of the anticipated acquisition of Westar, the ratio would increase up to a maximum of 0.75 to 1.00 for one year.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0		$ 10
Weighted-average interest rate from outstanding borrowings			1.94%
Amount of letters of credit outstanding	1		$ 0.2
Great Plains Energy [Member] | Bridge Loan [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	8,017	$ 8,017
Amount of bridge facility, as amended	5,100
Kansas City Power and Light Company [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 132.9		$ 180.3
Weighted-average interest rate from outstanding borrowings	0.98%		0.70%
Kansas City Power and Light Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 600
Revolving credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200
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
Amount of letters of credit outstanding	2.8		2.7
KCPL Greater Missouri Operations [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 201.9		$ 43.7
Weighted-average interest rate from outstanding borrowings	1.02%		0.65%
KCPL Greater Missouri Operations [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 450
Revolving credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200
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
Amount of letters of credit outstanding	$ 1.9		$ 2.5

Long-Term Debt (Details)

Long-Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Current maturities	$ (382.1)	$ (1.1)
Long-term debt excluding current maturities	3,365.2	3,745.1
Amortization of Financing Costs	33.8	4.1	$ 4.8
Long-term Debt, Fiscal Year Maturity [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	382.1
Long-term Debt, Maturities, Repayments of Principal in Year Two	351.1
Long-term Debt, Maturities, Repayments of Principal in Year Three	401.1
Long-term Debt, Maturities, Repayments of Principal in Year Four	1.1
Long-term Debt, Maturities, Repayments of Principal in Year Five	432
Kansas City Power and Light Company [Member]
Debt Instrument [Line Items]
Current maturities	(281)	0
Unamortized discount and premium, net and debt issuance costs	(15.4)	(17.3)
Long-term debt excluding current maturities	2,284	2,563.1
Amortization of Financing Costs	3.2	3	3
Long-term Debt, Fiscal Year Maturity [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	281
Long-term Debt, Maturities, Repayments of Principal in Year Two	350
Long-term Debt, Maturities, Repayments of Principal in Year Three	400
Long-term Debt, Maturities, Repayments of Principal in Year Four	0
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Kansas City Power and Light Company [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Principal outstanding	510.5	510.5
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage Bonds EIRR due 2017-2035 [Member]
Debt Instrument [Line Items]
Principal outstanding	110.5	110.5
EIRR bonds repurchased and held	$ 21.9	21.9
Debt Instrument Maturity Date Range End	Dec. 31, 2035
Debt Instrument Maturity Date Range Start	Dec. 31, 2017
Long-term Debt, Weighted Average Interest Rate	2.47%
KCPL Municipal Bond Insurance Policies [Abstract]
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
Insurance Agreement Covenant Indebtedness To Total Capitalization Ratio Maximum	75.00%
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%
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage bonds Series 2009A due 2019 [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 400	400
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%
Kansas City Power and Light Company [Member] | Secured Debt [Member] | General Mortgage bonds EIRR series 2005 [Member]
Debt Instrument [Line Items]
EIRR bonds repurchased and held	$ 50	50
KCPL Municipal Bond Insurance Policies [Abstract]
Principal outstanding covered by insurance policies	$ 50
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
Insurance Agreement Covenant Indebtedness To Total Capitalization Ratio Maximum	75.00%
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%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2017 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 250	250
Debt Instrument, Maturity Date	Dec. 31, 2017
Interest rates (in hundredths)	5.85%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	5.72%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2018 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 350	350
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%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior Notes due 2023 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 300	300
Debt Instrument, Maturity Date	Dec. 31, 2023
Interest rates (in hundredths)	3.15%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior Notes due 2025 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 350	350
Debt Instrument, Maturity Date	Dec. 31, 2025
Interest rates (in hundredths)	3.65%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior notes due 2035 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 250	250
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%
Kansas City Power and Light Company [Member] | Senior Notes [Member] | Senior Notes Due 2041 KCPL [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 400	400
Debt Instrument, Maturity Date	Dec. 31, 2041
Interest rates (in hundredths)	5.30%
Kansas City Power and Light Company [Member] | Unsecured Debt [Member] | EIRR Bonds Series 2007A and 2007B due 2035 [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 146.5	146.5
Debt Instrument, Maturity Date	Dec. 31, 2035
Variable rate (in hundredths)	0.694%
Kansas City Power and Light Company [Member] | Unsecured Debt [Member] | EIRR bonds 2.875 percent Series 2008 [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 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]
Principal outstanding	$ 5.7	6.8
Debt Instrument Maturity Date Range End	Dec. 31, 2021
Debt Instrument Maturity Date Range Start	Dec. 31, 2017
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]
Principal outstanding	$ 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]
Principal outstanding	$ 125	125
Debt Instrument, Maturity Date	Dec. 31, 2025
Interest rates (in hundredths)	3.49%
KCPL Municipal Bond Insurance Policies [Abstract]
Insurance Agreement 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
GMO Senior Notes [Abstract]
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]
Principal outstanding	$ 75	75
Debt Instrument, Maturity Date	Dec. 31, 2033
Interest rates (in hundredths)	4.06%
KCPL Municipal Bond Insurance Policies [Abstract]
Insurance Agreement 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.
Insurance Agreement Covenant Compliance	in compliance
KCPL Greater Missouri Operations [Member] | Senior Notes [Member] | Senior Notes Series C due 2043 [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 150	150
Debt Instrument, Maturity Date	Dec. 31, 2043
Interest rates (in hundredths)	4.74%
KCPL Municipal Bond Insurance Policies [Abstract]
Insurance Agreement 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.
Insurance Agreement 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]
Principal outstanding	$ 3	3
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]
Principal outstanding	$ 7	7
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
Long-term debt excluding current maturities	638.2	738.1
Great Plains Energy [Member] | Bridge Loan [Member]
Debt Instrument [Line Items]
Line Of Credit Facility Maximum Borrowing Capacity As Amended	5,100
Great Plains Energy [Member] | Senior Notes [Member] | Senior notes due 2017 [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 100	100
Debt Instrument, Maturity Date	Dec. 31, 2017
Interest rates (in hundredths)	6.875%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)	7.33%
Great Plains Energy [Member] | Senior Notes [Member] | Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 350	350
Debt Instrument, Maturity Date	Dec. 31, 2021
Interest rates (in hundredths)	4.85%
Great Plains Energy [Member] | Senior Notes [Member] | Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Principal outstanding	$ 287.5	287.5
Debt Instrument, Maturity Date	Dec. 31, 2022
Interest rates (in hundredths)	5.292%
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)	(2.1)
Amortization of Financing Costs	30.6	$ 1.1	$ 1.8
Other Consolidated Entities [Member] | Bridge Loan [Member]
Debt Instrument [Line Items]
Amortization of Financing Costs	$ 29.6

Common Shareholders' Equity (De

Common Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	Oct. 03, 2016	Oct. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2016
Common Shareholders' Equity [Line Items]
Common Stock, Shares Authorized			600,000,000	250,000,000		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)			1,000,000
Number of shares available under the defined contribution savings plan (in shares)			700,000
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. In addition, if preferred stock dividends are not declared and paid when scheduled, Great Plains Energy could not declare or pay common stock dividends or purchase any common shares. If the unpaid preferred stock dividends are in arrears for six or more quarters, whether or not consecutive, the preferred shareholders will be entitled to name two directors to the Great Plains Energy Board. 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, except as the ratio pertains to Great Plains Energy, which was amended in June 2016, as further described in Note 11.
Restricted net assets of subsidiaries			$ 2,800
Gross Proceeds from Issuance of Common Stock			$ 1,603.7	$ 3	$ 4.8
Common Stock [Member]
Common Shareholders' Equity [Line Items]
Shares Issued, Price Per Share	$ 26.45	$ 26.45
Gross Proceeds from Issuance of Common Stock	$ 1,600	$ 1,600
Net Proceeds from Issuance of Common Stock	$ 1,550	$ 1,550
Stock Issued During Period, Shares, New Issues	60,500,000	60,500,000	60,974,205	250,863	258,416

Preferred Stock (Details)

Preferred Stock (Details) $ / shares in Units, $ in Millions	Oct. 03, 2016USD ($)$ / sharesshares	May 29, 2016USD ($)Rateshares	Oct. 31, 2016USD ($)$ / sharesshares	Aug. 31, 2016USD ($)$ / sharesRateshares	Dec. 31, 2016USD ($)years$ / sharesRateshares	Dec. 31, 2015USD ($)$ / sharesRateshares	Dec. 31, 2014USD ($)
Cumulative Preferred Stock [Abstract]
Redemption of cumulative preferred stock | $					$ 40.1	$ 0	$ 0
No Par Preference Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized | shares					11,000,000	11,000,000
Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized | shares					390,000	390,000
Preferred Stock, Value, Issued | $					$ 0	$ 39
Cumulative preferred stock par value (in dollars per share)				$ 100	$ 100	$ 100
Cumulative Preferred Stock [Abstract]
Preferred Stock, Shares Redeemed | shares				390,000
Redemption of cumulative preferred stock | $				$ 40.1
Cumulative No Par Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Authorized | shares					1,600,000
Preferred Stock 3 Point 80 [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage | Rate				3.80%
Cumulative Preferred Stock [Abstract]
Preferred Stock, Redemption Price Per Share, Including Accrued and Unpaid Dividends				$ 104.45
Accrued and Unpaid Preferred Dividends Per Share				0.75
Preferred Stock, Redemption Price Per Share				$ 103.70
Preferred Stock 4 Point 20 [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage | Rate				4.20%
Cumulative Preferred Stock [Abstract]
Preferred Stock, Redemption Price Per Share, Including Accrued and Unpaid Dividends				$ 102.83
Accrued and Unpaid Preferred Dividends Per Share				0.83
Preferred Stock, Redemption Price Per Share				$ 102
Preferred Stock 4 Point 35 [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage | Rate				4.35%
Cumulative Preferred Stock [Abstract]
Preferred Stock, Redemption Price Per Share, Including Accrued and Unpaid Dividends				$ 101.86
Accrued and Unpaid Preferred Dividends Per Share				0.86
Preferred Stock, Redemption Price Per Share				$ 101
Preferred Stock 4 Point 50 [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage | Rate				4.50%
Cumulative Preferred Stock [Abstract]
Preferred Stock, Redemption Price Per Share, Including Accrued and Unpaid Dividends				$ 101.89
Accrued and Unpaid Preferred Dividends Per Share				0.89
Preferred Stock, Redemption Price Per Share				$ 101
7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage | Rate		7.25%			7.25%
Mandatory Convertible Preferred Stock [Abstract]
Preferred Shares To Be Issued, Stock Purchase Agreement, Series A Preferred Stock | shares		750,000			750,000
Preferred Stock, Purchase Agreement, Proceeds | $		$ 750
Preferred Stock, Years to Conversion | years					3
Applicable Market Value, Maximum, Series A					$ 34.38
Conversion Rate, if the Applicable Market Value is equal to or greater than $34.38					29.0855
Applicable Market Value, Minimum, Series A					$ 28.65
Conversion Rate, if the Applicable Market Value is less than or equal to $28.65					34.9026
Conversion Rate, Numerator, Series A					$ 1,000
Conversion Rate, Voluntary					29.0855
Preferred Stock, Liquidation Preference Per Share					$ 1,000
Preferred Stock, Voting Rights					OMERS will be entitled to name two directors to the Great Plains Energy Board if dividends payable with respect to the Series A Preferred Stock are in arrears for two quarters and one observer on the Great Plains Energy Board if Great Plains Energy's credit rating is downgraded to below investment grade, so long as OMERS holds 50 percent of its original investment and subject to all necessary governmental approvals being obtained.
7.00% Mandatory Convertible Preferred Stock, Series B
Class of Stock [Line Items]
Preferred Stock, Value, Issued | $					$ 836.2	$ 0
Preferred Stock, Dividend Rate, Percentage | Rate					7.00%	7.00%
Cumulative Preferred Stock [Abstract]
Preferred Stock, Shares Outstanding | shares					862,500
Mandatory Convertible Preferred Stock [Abstract]
Applicable Market Value, Maximum, Series B					$ 31.74
Conversion Rate, if the Applicable Market Value is equal to or greater than $31.74					31.5060
Applicable Market Value, Minimum, Series B					$ 26.45
Conversion Rate, if the Applicable Market Value is less than or equal to $26.45					37.8080
Conversion Rate, Numerator, Series B					$ 1,000
Conversion Rate, Voluntary					31.5060
Preferred Stock, Liquidation Preference Per Share					$ 1,000	$ 1,000
Preferred Stock, Voting Rights					Holders of the Series B Preferred Stock will be entitled to name two directors to the Great Plains Energy Board if dividends payable with respect to the Series B Preferred Stock are in arrears for six or more quarters, whether or not consecutive.
Depositary Shares [Member]
Mandatory Convertible Preferred Stock [Abstract]
Stock Issued During Period, Shares, New Issues | shares	17,300,000		17,300,000
Shares Issued, Price Per Share	$ 50		$ 50
Net Proceeds from Issuance of Depositary Shares | $	$ 836.2		$ 836.2
Gross Proceeds from Issuance of Depositary Shares | $	$ 862.5		$ 862.5
Depositary Shares, Liquidation Preference Per Share					$ 50
Minimum [Member] | 7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Mandatory Convertible Preferred Stock [Abstract]
Applicable Market Value Less Than Maximum Greater Than Minimum					28.65
Minimum [Member] | 7.00% Mandatory Convertible Preferred Stock, Series B
Mandatory Convertible Preferred Stock [Abstract]
Applicable Market Value Less Than Maximum Greater Than Minimum					26.45
Maximum [Member] | 7.25% Mandatory Convertible Preferred Stock, Series A [Member]
Mandatory Convertible Preferred Stock [Abstract]
Applicable Market Value Less Than Maximum Greater Than Minimum					34.38
Maximum [Member] | 7.00% Mandatory Convertible Preferred Stock, Series B
Mandatory Convertible Preferred Stock [Abstract]
Applicable Market Value Less Than Maximum Greater Than Minimum					$ 31.74

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies Contractual Commitments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Lease Expense [Abstract]
Lease expense	$ 15	$ 16.8	$ 16
Operating Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	12.9
Operating Leases, Future Minimum Payments, Due in Two Years	11
Operating Leases, Future Minimum Payments, Due in Three Years	9.3
Operating Leases, Future Minimum Payments, Due in Four Years	9.7
Operating Leases, Future Minimum Payments, Due in Five Years	9.7
Operating Leases, Future Minimum Payments, Due Thereafter	110.5
Operating Leases, Future Minimum Payments Due, Total	163.1
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	3.1
Capital Leases, Future Minimum Payments Due, Total	5.1
Total Commitments [Abstract]
Total Commitments, Due in Next Twelve Months	369.7
Total Commitments, Due within Two Years	236.5
Total Commitments, Due within Three Years	152.5
Total Commitments, Due within Four Years	117.1
Total Commitments, Due within Five Years	75.2
Total Commitments, Due Thereafter	715.3
Total Commitments Due	1,666.3
Public Utilities, Inventory, Fuel [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	259
Unrecorded Unconditional Purchase Obligation, Due within Two Years	145.8
Unrecorded Unconditional Purchase Obligation, Due within Three Years	62.2
Unrecorded Unconditional Purchase Obligation, Due within Four Years	53.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	11.2
Unrecorded Unconditional Purchase Obligation, Due after Five Years	100.8
Unrecorded Unconditional Purchase Obligation, Total	632.8
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	47.3
Unrecorded Unconditional Purchase Obligation, Due within Five Years	47.4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	462.2
Unrecorded Unconditional Purchase Obligation, Total	698.8
Other purchase commitments [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	50.1
Unrecorded Unconditional Purchase Obligation, Due within Two Years	32
Unrecorded Unconditional Purchase Obligation, Due within Three Years	33.3
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5.9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	6.5
Unrecorded Unconditional Purchase Obligation, Due after Five Years	38.7
Unrecorded Unconditional Purchase Obligation, Total	166.5
Kansas City Power and Light Company [Member]
Lease Expense [Abstract]
Lease expense	13.7	$ 15	$ 14
Operating Leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	12
Operating Leases, Future Minimum Payments, Due in Two Years	11
Operating Leases, Future Minimum Payments, Due in Three Years	9.3
Operating Leases, Future Minimum Payments, Due in Four Years	9.7
Operating Leases, Future Minimum Payments, Due in Five Years	9.7
Operating Leases, Future Minimum Payments, Due Thereafter	110.5
Operating Leases, Future Minimum Payments Due, Total	162.2
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	1.6
Capital Leases, Future Minimum Payments Due, Total	2.6
Total Commitments [Abstract]
Total Commitments, Due in Next Twelve Months	317.8
Total Commitments, Due within Two Years	196.5
Total Commitments, Due within Three Years	118.5
Total Commitments, Due within Four Years	84.8
Total Commitments, Due within Five Years	52.2
Total Commitments, Due Thereafter	570.8
Total Commitments Due	1,340.6
Reimbursement by Other Owners per Year (2017)	1.5
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	5.5
Kansas City Power and Light Company [Member] | Public Utilities, Inventory, Fuel [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	221.5
Unrecorded Unconditional Purchase Obligation, Due within Two Years	119.4
Unrecorded Unconditional Purchase Obligation, Due within Three Years	43.6
Unrecorded Unconditional Purchase Obligation, Due within Four Years	35.1
Unrecorded Unconditional Purchase Obligation, Due within Five Years	1.8
Unrecorded Unconditional Purchase Obligation, Due after Five Years	100.8
Unrecorded Unconditional Purchase Obligation, Total	522.2
Kansas City Power and Light Company [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	34.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	34.9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	324.9
Unrecorded Unconditional Purchase Obligation, Total	499
Kansas City Power and Light Company [Member] | Other purchase commitments [Member]
Purchase Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months	49.3
Unrecorded Unconditional Purchase Obligation, Due within Two Years	31.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years	30.6
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5
Unrecorded Unconditional Purchase Obligation, Due within Five Years	5.6
Unrecorded Unconditional Purchase Obligation, Due after Five Years	33
Unrecorded Unconditional Purchase Obligation, Total	$ 154.6

Commitments and Contingencies E

Commitments and Contingencies Environmental Matters (Details) T in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)T	Dec. 31, 2015USD ($)
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	$ 43.4
Estimate Of Environmental Capital Expenditures In Two Years	36.6
Estimate Of Environmental Capital Expenditures In Three Years	11.5
Estimate Of Environmental Capital Expenditures In Four Years	$ 14
Climate Change [Abstract]
CO2 produced per year (in millions of tons) | T	19
EPA nationwide CO2 emission reductions by 2030	32.00%
Remediation [Abstract]
Accrued environmental remediation expenses	$ 1.4	$ 1.4
MISSOURI
Climate Change [Abstract]
EPA Interim Co2 Goal Rate Reduction	26.00%
EPA Co2 Emission Reductions By 2030 By State	37.00%
KANSAS
Climate Change [Abstract]
EPA Interim Co2 Goal Rate Reduction	34.00%
EPA Co2 Emission Reductions By 2030 By State	44.00%
Kansas City Power and Light Company [Member]
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	$ 34.9
Estimate Of Environmental Capital Expenditures In Two Years	16.5
Estimate Of Environmental Capital Expenditures In Three Years	7.6
Estimate Of Environmental Capital Expenditures In Four Years	$ 13
Climate Change [Abstract]
CO2 produced per year (in millions of tons) | T	15
Remediation [Abstract]
Accrued environmental remediation expenses	$ 0.3	$ 0.3
KCPL Greater Missouri Operations [Member]
Remediation [Abstract]
Estimated amount of insurance proceeds available to cover qualified remediation expenses	$ 1.5

Legal Proceedings Loss Continge

Legal Proceedings Loss Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Loss recorded in other operating expenses		$ 17	$ 5.9	$ 4
GMO Western Energy Crisis [Member]
Loss Contingencies [Line Items]
Loss recorded in other operating expenses		7.5
MPS Merchant Services, Inc. [Member] | GMO Western Energy Crisis [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount	$ (7.5)	8
Estimated additional refunds entitled to receive		$ 12

Guarantees (Details)

Guarantees (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 135.3
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	$ 38.7
Guarantor Obligations, Term	expire in 2017 and 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	$ 96.6
Guarantor Obligations, Term	maturity dates ranging from 2017 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	$ 201.9
Guarantor Obligations, Origin and Purpose	guaranteed GMO's commercial paper program

Related Party Transactions an83

Related Party Transactions and Relationships (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Kansas City Power and Light Company [Member] | Money Pool [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 0	$ 0
Kansas City Power and Light Company [Member] | KCPL Greater Missouri Operations [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	64.6	50
KCPL net wholesale sales to GMO	0.8	0.2	$ 12.7
Kansas City Power and Light Company [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	194.4	183.6	$ 173.9
Kansas City Power and Light Company [Member] | Great Plains Energy [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 2.6	$ 15.8
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%

Derivative Instruments (Details

Derivative Instruments (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Futures contracts [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	$ 0		$ 26.6
Fair Value	0		(5.7)
Forward Contracts [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	9.8		15.6
Fair Value	2.4		3.1
Transmission Congestion Rights [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	3.7		5.6
Fair Value	1.3		(0.5)
Interest Rate Swap [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	4,415	$ 4,400	0
Fair Value	79.3		0
Kansas City Power and Light Company [Member] | Futures contracts [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	0		0.9
Fair Value	0		(0.1)
Kansas City Power and Light Company [Member] | Transmission Congestion Rights [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	2.7		4.1
Fair Value	$ 0.9		$ (0.4)

Derivative Instruments Cash Flo

Derivative Instruments Cash Flow Hedge (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Derivative [Line Items]
Cash Flow Hedge Loss to be Reclassified within Twelve Months	$ 7.8
Kansas City Power and Light Company [Member]
Derivative [Line Items]
Cash Flow Hedge Loss to be Reclassified within Twelve Months	$ 7.5

Derivative Instruments Offsetti

Derivative Instruments Offsetting Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 83.6	$ 3.3
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(0.5)	(0.2)
Derivative Asset	83.1	3.1
Derivative, Collateral, Obligation to Return Securities	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	83.1	3.1
Kansas City Power and Light Company [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	1.3	0.2
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(0.4)	(0.2)
Derivative Asset	0.9	0
Derivative, Collateral, Obligation to Return Securities	0	0
Derivative, Collateral, Obligation to Return Cash	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	$ 0.9	$ 0

Derivative Instruments Offset87

Derivative Instruments Offsetting Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 0.6	$ 6.4
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(0.5)	(5.9)
Derivative Liability	0.1	0.5
Derivative, Collateral, Right to Reclaim Securities	0	0
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0.1	0.5
Cash collateral posted with counterparties		5.7
Kansas City Power and Light Company [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	0.4	0.7
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(0.4)	(0.3)
Derivative Liability	0	0.4
Derivative, Collateral, Right to Reclaim Securities	0	0
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 0	$ 0.4

Derivative Instruments Fair Val

Derivative Instruments Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 83.6	$ 3.3
Derivative Liability, Fair Value, Gross Liability	0.6	6.4
Kansas City Power and Light Company [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1.3	0.2
Derivative Liability, Fair Value, Gross Liability	0.4	0.7
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Balance Sheet Location [Member] | Kansas City Power and Light Company [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1.3	0.2
Derivative Liability, Fair Value, Gross Liability	0.4	0.7
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Other/Derivative Instruments
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	4.3	3.3
Derivative Liability, Fair Value, Gross Liability	0.6	$ 6.4
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	79.3
Derivative Liability, Fair Value, Gross Liability	$ 0

Derivative Instruments Gain and

Derivative Instruments Gain and Losses (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reflected in the income statement or regulatory account for changes in fair value of commodity contracts not designated as hedging	$ 81.4	$ (19)	$ (20.3)
Regulatory Asset [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in regulatory account for changes in fair value of commodity contracts not designated as hedging	0	(6.8)	(2.7)
Regulatory Liability [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in regulatory account for changes in fair value of commodity contracts not designated as hedging	1.3	0	0
Kansas City Power and Light Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reflected in the income statement or regulatory account for changes in fair value of commodity contracts not designated as hedging	4.6	(7.2)	(13.3)
Kansas City Power and Light Company [Member] | Regulatory Asset [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in regulatory account for changes in fair value of commodity contracts not designated as hedging	0	(0.5)	(0.2)
Kansas City Power and Light Company [Member] | Regulatory Liability [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in regulatory account for changes in fair value of commodity contracts not designated as hedging	1	0	0
Electric Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	3.5	(8.2)	(14.2)
Electric Revenues [Member] | Kansas City Power and Light Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	3.5	(8.2)	(14.2)
Fuel And Purchased Power Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	(2.7)	(4)	(3.4)
Fuel And Purchased Power Expense [Member] | Kansas City Power and Light Company [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	0.1	1.5	1.1
Interest Charges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reflected in the income statement for changes in fair value of commodity contracts not designated as hedging	$ 79.3	$ 0	$ 0

Fair Value Measurements Level 3

Fair Value Measurements Level 3 (Details) - Derivative Financial Instruments, Assets [Member] - Fair Value, Inputs, Level 3 [Member] - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net asset (liability) at beginning of period	$ (0.1)	$ 3.5
Purchases	0.3	0
Settlements	(15.5)	(2)
Net asset (liability) at end of period	80.9	(0.1)
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	11.3	8.6
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	0.1	(0.2)
Fuel And Purchased Power Expense [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	0.8	(1.5)
Electric Revenues [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	3.5	(8.2)
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	79.3	0
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	79.3	0
Regulatory (Asset) Liability [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 Regulatory Account	1.3	(0.5)
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	1.3	(0.5)
Kansas City Power and Light Company [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net asset (liability) at beginning of period	(0.4)	3.1
Purchases	(0.3)	(0.8)
Settlements	(2.9)	5.9
Net asset (liability) at end of period	0.9	(0.4)
Kansas City Power and Light Company [Member] | Electric Revenues [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	3.5	(8.2)
Kansas City Power and Light Company [Member] | Regulatory (Asset) Liability [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 Regulatory Account	1	(0.4)
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	$ 1	$ (0.4)

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Long-Term Debt (Details) - USD ($) $ in Billions	Dec. 31, 2016	Dec. 31, 2015
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	$ 3.8	$ 3.7
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Kansas City Power and Light Company [Member]
Fair value of financial instruments [Abstract]
Long-term Debt	2.6	2.6
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	4	4
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member] | Kansas City Power and Light Company [Member]
Fair value of financial instruments [Abstract]
Long-term debt fair value	$ 2.7	$ 2.8

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Millions	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Assets [Abstract]
Derivative instruments, assets	$ 83.6	$ 3.3
Liabilities [Abstract]
Derivative instruments, liabilities	0.6	6.4
Kansas City Power and Light Company [Member]
Assets [Abstract]
Derivative instruments, assets	1.3	0.2
Liabilities [Abstract]
Derivative instruments, liabilities	0.4	0.7
Other Consolidated Entities [Member] | Fixed Income Funds [Member]
SERP rabbi trust [Abstract]
Alternative Investments, Fair Value Disclosure	16	16.6
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Derivative instruments, assets	83.6	3.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	222.9	200.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.3	13.6
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure		0.1
Total assets	317.8	217.7
Liabilities [Abstract]
Derivative instruments, liabilities	0.6	6.4
Total liabilities	0.6	6.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0	0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	185.5	165.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	6.6	6.3
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure		0.1
Total assets	192.1	171.8
Liabilities [Abstract]
Derivative instruments, liabilities	0	5.7
Total liabilities	0	5.7
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	2.2	2.7
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	37.4	35.3
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	4.7	7.3
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure		0
Total assets	44.3	45.3
Liabilities [Abstract]
Derivative instruments, liabilities	0.1	0
Total liabilities	0.1	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	81.4	0.6
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure		0
Total assets	81.4	0.6
Liabilities [Abstract]
Derivative instruments, liabilities	0.5	0.7
Total liabilities	0.5	0.7
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member]
Assets [Abstract]
Derivative instruments, assets	1.3	0.2
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	222.9	200.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.3	13.6
SERP rabbi trust [Abstract]
Total assets	235.5	214.5
Liabilities [Abstract]
Derivative instruments, liabilities	0.4	0.7
Total liabilities	0.4	0.7
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	153.9	135.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.9	1.1
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	4.8	7.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	27.8	26.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	1.7	1.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.2	4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	32.4	29.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1	0.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.8	3.6
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	5.6	5.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0	0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	185.5	165.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	6.6	6.3
SERP rabbi trust [Abstract]
Total assets	192.1	171.7
Liabilities [Abstract]
Derivative instruments, liabilities	0	0.1
Total liabilities	0	0.1
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	153.9	135.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.9	1.1
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.1	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	27.8	26.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.8	3.6
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	5.6	5.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	0	0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	37.4	35.3
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	4.7	7.3
SERP rabbi trust [Abstract]
Total assets	42.1	42.6
Liabilities [Abstract]
Derivative instruments, liabilities	0	0
Total liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	4.7	7.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	1.7	1.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	3.2	4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	32.4	29.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1	0.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	1.3	0.2
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
SERP rabbi trust [Abstract]
Total assets	1.3	0.2
Liabilities [Abstract]
Derivative instruments, liabilities	0.4	0.6
Total liabilities	0.4	0.6
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member]
Assets [Abstract]
Derivative instruments, assets		3.1
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure		0.1
Total assets	82.3	3.2
Liabilities [Abstract]
Derivative instruments, liabilities		5.7
Total liabilities	0.2	5.7
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Commodity Contract [Member]
Assets [Abstract]
Derivative instruments, assets	3
Liabilities [Abstract]
Derivative instruments, liabilities	0.2
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	$ 79.3
Liabilities [Abstract]
Fair Value Inputs, Contingency Factor	0.35
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets		0
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure		0.1
Total assets	$ 0	0.1
Liabilities [Abstract]
Derivative instruments, liabilities		5.6
Total liabilities	0	5.6
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 1 [Member] | Commodity Contract [Member]
Assets [Abstract]
Derivative instruments, assets	0
Liabilities [Abstract]
Derivative instruments, liabilities	0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets		2.7
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure		0
Total assets	2.2	2.7
Liabilities [Abstract]
Derivative instruments, liabilities		0
Total liabilities	0.1	0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 2 [Member] | Commodity Contract [Member]
Assets [Abstract]
Derivative instruments, assets	2.2
Liabilities [Abstract]
Derivative instruments, liabilities	0.1
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets		0.4
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure		0
Total assets	80.1	0.4
Liabilities [Abstract]
Derivative instruments, liabilities		0.1
Total liabilities	0.1	$ 0.1
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member]
Assets [Abstract]
Derivative instruments, assets	0.8
Liabilities [Abstract]
Derivative instruments, liabilities	0.1
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	$ 79.3

Accumulated Other Comprehensi93

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (12)	$ (18.7)
Other comprehensive income (loss) before reclassifications	(0.7)	0.6
Amounts reclassified from accumulated other comprehensive loss	6.1	6.1
Net current period other comprehensive income	5.4	6.7	$ 6.6
Ending balance	(6.6)	(12)	(18.7)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(10.1)	(15.8)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	5.6	5.7
Net current period other comprehensive income	5.6	5.7
Ending balance	(4.5)	(10.1)	(15.8)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1.9)	(2.9)
Other comprehensive income (loss) before reclassifications	(0.7)	0.6
Amounts reclassified from accumulated other comprehensive loss	0.5	0.4
Net current period other comprehensive income	(0.2)	1
Ending balance	(2.1)	(1.9)	(2.9)
Kansas City Power and Light Company [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(9.6)
Net current period other comprehensive income	5.4	5.3	5.3
Ending balance	(4.2)	(9.6)
Kansas City Power and Light Company [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(9.6)	(14.9)
Amounts reclassified from accumulated other comprehensive loss	5.4	5.3
Net current period other comprehensive income	5.4	5.3
Ending balance	$ (4.2)	$ (9.6)	$ (14.9)

Accumulated Other Comprehensi94

Accumulated Other Comprehensive Income (Loss) Reclassification (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges									$ (161.5)	$ (199.3)	$ (188.5)
Utility operating and maintenance expenses									(759.5)	(724.8)	(701.9)
Income before income tax expense and income from equity investments									460.2	334.5	358.5
Income tax benefit									(172.2)	(122.7)	(115.7)
Net income	$ 98	$ 133.6	$ 32	$ 26.4	$ 22.9	$ 126.8	$ 44.4	$ 18.9
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income									(6.1)	(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 before income tax expense and income from equity investments									(9.2)	(9.2)
Income tax benefit									3.6	3.5
Net income									(5.6)	(5.7)
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									(9.2)	(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									(0.8)	(0.7)
Income before income tax expense and income from equity investments									(0.8)	(0.7)
Income tax benefit									0.3	0.3
Net income									(0.5)	(0.4)
Kansas City Power and Light Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges									(139.4)	(135.6)	(124.1)
Utility operating and maintenance expenses									(525.8)	(494.2)	(489.1)
Income before income tax expense and income from equity investments									346.9	229.6	238.1
Income tax benefit									(121.9)	(76.8)	$ (75.7)
Net income	$ 16.8	$ 117.7	$ 65.9	$ 24.6	$ 25.9	$ 84.3	$ 29.4	$ 13.2
Kansas City Power and Light Company [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 before income tax expense and income from equity investments									(8.8)	(8.7)
Income tax benefit									3.4	3.4
Net income									(5.4)	(5.3)
Kansas City Power and Light Company [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									$ (8.8)	$ (8.7)

Income Tax Expense (Details)

Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current income taxes
Federal	$ 0.3	$ (0.2)	$ 0.4
State	0.7	(1.1)	(0.1)
Total	1	(1.3)	0.3
Deferred income taxes
Federal	140.6	96.9	104.2
State	29.5	28	21.6
Total	170.1	124.9	125.8
Noncurrent income taxes
Federal	0	0	(2.4)
State	0	0	(0.5)
Foreign	0	0	(6.1)
Total	0	0	(9)
Investment tax credit
Deferral	2.5	0.5	0
Amortization	(1.4)	(1.4)	(1.4)
Total	1.1	(0.9)	(1.4)
Total income tax expense	$ 172.2	$ 122.7	$ 115.7
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%)	0.00%	(0.70%)
Amortization of investments tax credits (in hundredths)	(0.30%)	(0.40%)	(0.40%)
Federal income tax credits (in hundredths)	(2.60%)	(4.10%)	(3.80%)
State income taxes (in hundredths)	4.20%	4.00%	3.80%
Changes in uncertain tax positions, net (in hundredths)	0.00%	0.00%	(1.70%)
Transaction costs (in hundredths)	0.90%	0.00%	0.00%
Valuation allowance	0.00%	1.50%	0.00%
Other (in hundredths)	0.20%	0.50%	0.10%
Effective income tax rate (in hundredths)	37.30%	36.50%	32.30%
Kansas City Power and Light Company [Member]
Current income taxes
Federal	$ 24.8	$ (18.7)	$ (9.4)
State	4.7	(3.4)	(2.3)
Total	29.5	(22.1)	(11.7)
Deferred income taxes
Federal	76.4	81.9	72.6
State	17	17.5	15.8
Total	93.4	99.4	88.4
Investment tax credit
Deferral	0	0.5	0
Amortization	(1)	(1)	(1)
Total	(1)	(0.5)	(1)
Total income tax expense	$ 121.9	$ 76.8	$ 75.7
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)	(0.30%)	0.00%	(0.90%)
Amortization of investments tax credits (in hundredths)	(0.30%)	(0.50%)	(0.40%)
Federal income tax credits (in hundredths)	(3.10%)	(5.60%)	(5.60%)
State income taxes (in hundredths)	4.10%	4.00%	3.70%
Valuation allowance	0.00%	0.30%	0.00%
Other (in hundredths)	(0.20%)	0.30%	0.00%
Effective income tax rate (in hundredths)	35.20%	33.50%	31.80%

Taxes Deferred Income Taxes (De

Taxes Deferred Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets (Liabilities), Net of Valuation Allowance, Noncurrent Classification [Abstract]
Plant related	$ (2,107.6)	$ (1,967)
Income taxes on future regulatory recoveries	(148.7)	(151.3)
Deferred Tax Assets, Derivative Instruments		20.5
Deferred Tax Liabilities, Derivative Instruments	(17)
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions	10.5
Deferred Tax Liabilities, Compensation and Benefits, Pensions		(0.1)
SO2 emission allowance sales	24.1	25.7
Fuel recovery mechanisms	(22.3)	(4.5)
Tax credit carryforwards	271.1	256.8
Customer demand programs	(34.3)	(22.7)
Solar rebates	(27.3)	(31.9)
Net operating loss carryforward	718	734.9
Deferred Tax Assets, Other	20.2	0.7
Net noncurrent deferred income tax liability before valuation allowance	(1,313.3)	(1,138.9)
Valuation allowance	(16.4)	(19.9)
Net noncurrent deferred income tax liability	(1,329.7)	(1,158.8)
Net deferred income tax liability	(1,329.7)	(1,158.8)
Deferred Tax Assets (Liabilities), Gross [Abstract]
Gross deferred income tax assets	1,360.9	1,368.5
Gross deferred income tax liabilities	(2,690.6)	(2,527.3)
Net deferred income tax liability	(1,329.7)	(1,158.8)
Kansas City Power and Light Company [Member]
Deferred Tax Assets (Liabilities), Net of Valuation Allowance, Noncurrent Classification [Abstract]
Plant related	(1,492.2)	(1,398.9)
Income taxes on future regulatory recoveries	(123.9)	(125)
Deferred Tax Assets, Derivative Instruments	8.5	14
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions	38.6	27.4
SO2 emission allowance sales	24.1	25.7
Fuel recovery mechanisms	(27.2)	(6.3)
Tax credit carryforwards	177.4	166.6
Customer demand programs	(21.8)	(16.9)
Solar rebates	(11.4)	(13.1)
Net operating loss carryforward	198.3	204.2
Deferred Tax Assets, Other	1.3
Deferred Tax Liabilities, Other		(9.6)
Net noncurrent deferred income tax liability before valuation allowance	(1,228.3)	(1,131.9)
Valuation allowance	0	(0.7)
Net noncurrent deferred income tax liability	(1,228.3)	(1,132.6)
Net deferred income tax liability	(1,228.3)	(1,132.6)
Deferred Tax Assets (Liabilities), Gross [Abstract]
Gross deferred income tax assets	747.7	740.9
Gross deferred income tax liabilities	(1,976)	(1,873.5)
Net deferred income tax liability	$ (1,228.3)	$ (1,132.6)

Taxes Net Operating Loss Carryf

Taxes Net Operating Loss Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 643.8	$ 656.1
Amount of Net Operating Losses related to business acquisition	306.2	313.2
Net operating losses year of origination [Abstract]
Net operating loss carryforwards originating in 2003	23
Net operating loss carryfowards originating in 2004	152.4
Net operating loss carryfowards originating in 2005	74.1
Net operating loss carryfowards originating in 2006	53.3
Net operating loss carryfowards originating in 2007	1.3
Net operating loss carryfowards originating in 2008	2.4
Net operating loss carryfowards originating in 2009	36.5
Net operating loss carryfowards originating in 2010	4.1
Net operating loss carryfowards originating in 2011	108.8
Net operating loss carryforwards originating in 2012	2.1
Net operating loss carryforwards originating in 2013	1.4
Net operating loss carryforwards originating in 2014	86.3
Net operating loss carryforwards originating in 2015	$ 98.1
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	$ 74.2	78.8
Amount of Net Operating Losses related to business acquisition	36.1	$ 39.2
Operating Loss Carryforwards, Valuation Allowance	$ 16

Taxes Tax Credit Carryforwards

Taxes Tax Credit Carryforwards (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Tax Credit Carryforward [Line Items]
Valuation Allowance, Deferred Tax Asset, Explanation of Change	tax expense was recorded in continuing operations primarily related to state NOL carryforwards that expired at December 31, 2016.
General Business Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 183.5	$ 169.2
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	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] | Minimum [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, 2036
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.	These credits do not expire and can be used to reduce taxes paid in the future.
Kansas City Power and Light Company [Member] | General Business Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 177.4	$ 166.6
Tax Credit Carryforward, Description	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits	relate primarily to Advanced Coal Investment Tax Credits and Wind Production tax credits
Kansas City Power and Light Company [Member] | General Business Tax Credit Carryforward [Member] | Minimum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2028
Kansas City Power and Light Company [Member] | General Business Tax Credit Carryforward [Member] | Maximum [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2036

Taxes Valuation Allowance (Deta

Taxes Valuation Allowance (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Valuation Allowance [Line Items]
Valuation Allowance, Deferred Tax Asset, Change in Amount	$ 3.5
Valuation Allowance, Deferred Tax Asset, Explanation of Change	tax expense was recorded in continuing operations primarily related to state NOL carryforwards that expired at December 31, 2016.

Segments and Related Informa100

Segments and Related Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 576.3	$ 856.8	$ 670.8	$ 572.1	$ 562.7	$ 781.4	$ 609	$ 549.1	$ 2,676	$ 2,502.2	$ 2,568.2
Depreciation and amortization									(344.8)	(330.4)	(306)
Interest charges									(161.5)	(199.3)	(188.5)
Income tax (expense) benefit									(172.2)	(122.7)	(115.7)
Net income (loss)									290	213	242.8
Assets	13,570				10,738.6				13,570	10,738.6	10,453.4
Capital expenditures									609.4	677.1	773.7
Operating Segments [Member] | Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,676	2,502.2	2,568.2
Depreciation and amortization									(344.8)	(330.4)	(306)
Interest charges									(196.1)	(190.9)	(183)
Income tax (expense) benefit									(164.3)	(120.8)	(125.6)
Net income (loss)									292.1	223.8	243.5
Assets	11,444.2				11,045.5				11,444.2	11,045.5	10,727.7
Capital expenditures									609.4	677.1	773.7
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Depreciation and amortization									0	0	0
Interest charges									2.5	(40.5)	(41.2)
Income tax (expense) benefit									(7.9)	(1.9)	9.9
Net income (loss)									(2.1)	(10.8)	(0.7)
Assets	2,461.3				(51.1)				2,461.3	(51.1)	29.2
Capital expenditures									0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Depreciation and amortization									0	0	0
Interest charges									32.1	32.1	35.7
Income tax (expense) benefit									0	0	0
Net income (loss)									0	0	0
Assets	$ (335.5)				$ (255.8)				(335.5)	(255.8)	(303.5)
Capital expenditures									$ 0	$ 0	$ 0

Jointly Owned Electric Utili101

Jointly Owned Electric Utility Plants (Details) $ in Millions	Dec. 31, 2016USD ($)MW	Dec. 31, 2015USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Nuclear fuel, net	$ 62	$ 68.3
Jeffrey Energy Center [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	8.00%
Utility plant in service	$ 196.1
Accumulated depreciation	80.1
Nuclear fuel, net	0
Construction work in progress	$ 3.7
Accredited capacity | MW	172
Iatan Common [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	79.00%
Utility plant in service	$ 490.6
Accumulated depreciation	126.3
Nuclear fuel, net	0
Construction work in progress	$ 22.1
Iatan No. 2 [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	73.00%
Utility plant in service	$ 1,334.9
Accumulated depreciation	387.3
Nuclear fuel, net	0
Construction work in progress	$ 41.7
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	$ 670.2
Accumulated depreciation	261.6
Nuclear fuel, net	0
Construction work in progress	$ 19.9
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	$ 1,099.5
Accumulated depreciation	275.6
Nuclear fuel, net	0
Construction work in progress	$ 30.6
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	$ 1,853.1
Accumulated depreciation	889.6
Nuclear fuel, net	62
Construction work in progress	$ 83.5
Accredited capacity | MW	549
Kansas City Power and Light Company [Member]
Jointly Owned Utility Plant Interests [Line Items]
Nuclear fuel, net	$ 62	$ 68.3
Kansas City Power and Light Company [Member] | Iatan Common [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	61.00%
Utility plant in service	$ 403.1
Accumulated depreciation	113
Nuclear fuel, net	0
Construction work in progress	$ 5
Kansas City Power and Light Company [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	$ 1,022.4
Accumulated depreciation	346.6
Nuclear fuel, net	0
Construction work in progress	$ 23.1
Accredited capacity | MW	482
Kansas City Power and Light Company [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	$ 532.8
Accumulated depreciation	210.8
Nuclear fuel, net	0
Construction work in progress	$ 8.4
Accredited capacity | MW	490
Kansas City Power and Light Company [Member] | LaCygne Station [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%
Utility plant in service	$ 1,099.5
Accumulated depreciation	275.6
Nuclear fuel, net	0
Construction work in progress	$ 30.6
Accredited capacity | MW	699
Kansas City Power and Light Company [Member] | Wolf Creek [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	47.00%
Utility plant in service	$ 1,853.1
Accumulated depreciation	889.6
Nuclear fuel, net	62
Construction work in progress	$ 83.5
Accredited capacity | MW	549

Quarterly Operating Results 102

Quarterly Operating Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating revenues	$ 576.3	$ 856.8	$ 670.8	$ 572.1	$ 562.7	$ 781.4	$ 609	$ 549.1	$ 2,676	$ 2,502.2	$ 2,568.2
Operating income	64.8	281.9	182.3	89.9	83.4	256.7	119.9	70.1	$ 618.9	$ 530.1	$ 534.5
Net income	$ 98	$ 133.6	$ 32	$ 26.4	$ 22.9	$ 126.8	$ 44.4	$ 18.9
Basic and diluted earnings per common share	$ 0.39	$ 0.86	$ 0.20	$ 0.17	$ 0.15	$ 0.82	$ 0.28	$ 0.12	$ 1.61	$ 1.37	$ 1.57
Kansas City Power and Light Company [Member]
Operating revenues	$ 401.3	$ 597.6	$ 475.6	$ 400.9	$ 399.7	$ 526.3	$ 417.4	$ 370.4	$ 1,875.4	$ 1,713.8	$ 1,730.8
Operating income	54.4	219.2	137.9	70.6	68.6	170.8	79.3	45.3	$ 482.1	$ 364	$ 350.1
Net income	$ 16.8	$ 117.7	$ 65.9	$ 24.6	$ 25.9	$ 84.3	$ 29.4	$ 13.2

Schedule I Financial Statements

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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Expenses
Costs to achieve the anticipated acquisition of Westar Energy, Inc.									$ 34.2	$ 0	$ 0
General taxes									226.7	213.2	204.6
Operating income	$ 64.8	$ 281.9	$ 182.3	$ 89.9	$ 83.4	$ 256.7	$ 119.9	$ 70.1	618.9	530.1	534.5
Equity in earnings (loss) from Subsidiaries									2	1.2	0
Interest charges									(161.5)	(199.3)	(188.5)
Income before income tax expense and income from equity investments									460.2	334.5	358.5
Income tax expense									(172.2)	(122.7)	(115.7)
Net income (loss)	$ 98	$ 133.6	$ 32	$ 26.4	$ 22.9	$ 126.8	$ 44.4	$ 18.9
Preferred stock dividend requirements and redemption premium									16.5	1.6	1.6
Earnings available for common shareholders									$ 273.5	$ 211.4	$ 241.2
Average number of basic common shares outstanding									169.4	154.2	153.9
Average number of diluted common shares outstanding									169.8	154.8	154.1
Basic and diluted earnings per common share	$ 0.39	$ 0.86	$ 0.20	$ 0.17	$ 0.15	$ 0.82	$ 0.28	$ 0.12	$ 1.61	$ 1.37	$ 1.57
Common Stock, Dividends, Per Share, Declared									$ 1.0625	$ 0.9975	$ 0.935
Comprehensive Income
Net income (loss)	$ 98	$ 133.6	$ 32	$ 26.4	$ 22.9	$ 126.8	$ 44.4	$ 18.9
Other comprehensive income
Reclassification to expenses, net of tax									$ 5.6	$ 5.7	$ 8
Derivative hedging activity, net of tax									5.6	5.7	8
Total other comprehensive income									5.4	6.7	6.6
Comprehensive income									295.4	219.7	249.4
Great Plains Energy [Member]
Operating Expenses
General and administrative									2.7	0.9	1.1
Costs to achieve the anticipated acquisition of Westar Energy, Inc.									18.3	0	0
General taxes									0.1	0.2	0.4
Operating Expenses									21.1	1.1	1.5
Operating income									(21.1)	(1.1)	(1.5)
Equity in earnings (loss) from Subsidiaries									287.5	220.9	251.1
Non-operating income									31.3	29.7	33.1
Interest charges									2.6	(40.3)	(44.3)
Income before income tax expense and income from equity investments									300.3	209.2	238.4
Income tax expense									(10.3)	3.8	4.4
Net income (loss)									290	213	242.8
Preferred stock dividend requirements and redemption premium									16.5	1.6	1.6
Earnings available for common shareholders									$ 273.5	$ 211.4	$ 241.2
Average number of basic common shares outstanding									169.4	154.2	153.9
Average number of diluted common shares outstanding									169.8	154.8	154.1
Basic and diluted earnings per common share									$ 1.61	$ 1.37	$ 1.57
Comprehensive Income
Net income (loss)									$ 290	$ 213	$ 242.8
Other comprehensive income
Reclassification to expenses									0.4	0.5	4.4
Income tax (expense) benefit on reclassification to expenses									(0.2)	(0.1)	(1.7)
Reclassification to expenses, net of tax									0.2	0.4	2.7
Derivative hedging activity, net of tax									0.2	0.4	2.7
Other comprehensive income from subsidiaries, net of tax									5.2	6.3	3.9
Total other comprehensive income									5.4	6.7	6.6
Comprehensive income									$ 295.4	$ 219.7	$ 249.4

Schedule I Financial Stateme104

Schedule I Financial Statements of Parent Company Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current Assets
Cash and Cash Equivalents, at Carrying Value	$ 1,293.1	$ 11.3	$ 13	$ 10.6
Taxes receivable	0	3.8
Derivative Asset, Current	81.5	0.8
Total	3,059.5	664.2
Investments and Other Assets
Other	113.9	63.2
Assets	13,570	10,738.6	10,453.4
Current Liabilities
Notes payable	0	10
Current maturities of long-term debt	382.1	1.1
Accrued taxes	33.3	31.6
Accrued interest	50.8	44.7
Other	32.6	31.6
Total	1,384.8	915.7
Deferred Credits and Other Liabilities
Liabilities, Noncurrent, Total	2,658	2,382.3
Capitalization
Common stock	4,217	2,646.7
Retained earnings	1,119.2	1,024.4
Treasury stock - 128,087 and 101,229 shares, at cost	(3.8)	(2.6)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(6.6)	(12)	(18.7)
Total shareholders' equity	6,162	3,695.5	3,625.1
Long-term debt (Note 12)	3,365.2	3,745.1
Total	9,527.2	7,440.6
Commitments and Contingencies
Total	13,570	10,738.6
Great Plains Energy [Member]
Current Assets
Cash and Cash Equivalents, at Carrying Value	1,283.9	0	$ 0	$ 0
Time deposit	1,000	0
Accounts receivable from subsidiaries	10.6	4.1
Notes receivable from subsidiaries, current	2	2
Money pool receivable	0	3.7
Derivative Asset, Current	79.3	0
Other current assets	26.1	0.4
Total	2,401.9	10.2
Investments and Other Assets
Investment in KCP&L	2,541.5	2,433.1
Investment in other subsidiaries	1,341.6	1,385.9
Notes receivable from subsidiaries, noncurrent	634.9	634.9
Deferred income taxes	12.8	34.8
Other	16.3	1.6
Total investments and other assets	4,547.1	4,490.3
Assets	6,949	4,500.5
Current Liabilities
Notes payable	0	10
Current maturities of long-term debt	100	0
Accounts payable to subsidiaries	10.8	31.7
Accrued taxes	12.9	4.5
Accrued interest	10.1	4.1
Other	12.8	9.5
Total	146.6	59.8
Deferred Credits and Other Liabilities
Liabilities, Noncurrent, Total	2.2	7.1
Capitalization
Common stock	4,217	2,646.7
Retained earnings	1,119.2	1,024.4
Treasury stock - 128,087 and 101,229 shares, at cost	(3.8)	(2.6)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(6.6)	(12)
Total shareholders' equity	6,162	3,695.5
Long-term debt (Note 12)	638.2	738.1
Total	6,800.2	4,433.6
Commitments and Contingencies
Total	6,949	4,500.5
Cumulative Preferred Stock [Member]
Capitalization
Preferred Stock, Value, Issued	0	39
Cumulative Preferred Stock [Member] | Great Plains Energy [Member]
Capitalization
Preferred Stock, Value, Issued	0	39
Preference Stock | Great Plains Energy [Member]
Capitalization
Preferred Stock, Value, Issued	$ 836.2	$ 0

Schedule I Financial Stateme105

Schedule I Financial Statements of Parent Company Balance Sheet Parenthetical (Details) - USD ($)	1 Months Ended	12 Months Ended
	Aug. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
Nuclear Fuel Accumulated Amortization		$ 172,100,000	$ 192,500,000
Common Stock, Shares Authorized		600,000,000	250,000,000	600,000,000
Common Stock, Shares, Issued		215,479,105	154,504,900
Treasury Stock, Shares		128,087	101,229
Great Plains Energy [Member]
Common Stock, Shares Authorized		600,000,000	250,000,000
Common Stock, Shares, Issued		215,479,105	154,504,900
Treasury Stock, Shares		128,087	101,229
Preferred Stock, Shares Authorized		11,000,000	0
Cumulative Preferred Stock [Member]
Cumulative preferred stock par value (in dollars per share)	$ 100	$ 100	$ 100
Preferred Stock, Shares Authorized		390,000	390,000
Preferred Stock, Shares Issued		0	390,000
Cumulative Preferred Stock [Member] | Great Plains Energy [Member]
Cumulative preferred stock par value (in dollars per share)		$ 100	$ 100
Preferred Stock, Shares Issued		0	390,000
Preferred Stock 3 Point 80 [Member]
Preferred Stock, Dividend Rate, Percentage	3.80%
Preferred Stock 4 Point 50 [Member]
Preferred Stock, Dividend Rate, Percentage	4.50%
Preferred Stock 4 Point 20 [Member]
Preferred Stock, Dividend Rate, Percentage	4.20%
Preferred Stock 4 Point 35 [Member]
Preferred Stock, Dividend Rate, Percentage	4.35%
Series B Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage		7.00%	7.00%
Preferred Stock, Shares Issued		862,500	0
Series B Preferred Stock [Member] | Great Plains Energy [Member]
Preferred Stock, Dividend Rate, Percentage		7.00%	0.00%
Preferred Stock, Shares Issued		862,500	0
Preferred Stock, Liquidation Preference, Value		$ 1,000	$ 0

Schedule I Financial Stateme106

Schedule I Financial Statements of Parent Company Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Flows from Operating Activities
Net income (loss)	$ 98	$ 133.6	$ 32	$ 26.4	$ 22.9	$ 126.8	$ 44.4	$ 18.9
Adjustments to reconcile income to net cash from operating activities:
Deferred income taxes, net									$ 170.1	$ 124.9	$ 125.8
Equity in earnings from subsidiaries									(2)	(1.2)	0
Fair value impact of interest rate swaps									(79.3)	0	0
Cash flows affected by changes in:
Accrued taxes									8.1	1.1	8.3
Accrued interest									6.1	3.4	(4.1)
Other									15.2	(2.9)	(12.3)
Net cash from operating activities									784	753.1	698.2
Cash Flows from Investing Activities
Purchase of time deposit									(1,000)	0	0
Other investing activities									(64)	(48.2)	(27.5)
Net cash from investing activities									(1,683.5)	(734.4)	(779.8)
Cash Flows from Financing Activities
Issuance of common stock									1,603.7	3	4.8
Issuance of preference stock									862.5	0	0
Issuance of long-term debt									0	348.8	0
Issuance fees									(143.6)	(3)	(0.9)
Repayment of long-term debt									(1.1)	(87)	(13.4)
Net change in short-term borrowings									100.8	(128.3)	245.1
Dividends paid									(194)	(155.5)	(145.6)
Redemption of cumulative preferred stock									(40.1)	0	0
Purchase of treasury stock									(5)	(1.6)	(2.5)
Other financing activities									0.7	(0.8)	0.5
Net cash from financing activities									2,181.3	(20.4)	84
Net Change in Cash and Cash Equivalents									1,281.8	(1.7)	2.4
Cash and Cash Equivalents at Beginning of Year				11.3				13	11.3	13	10.6
Cash and Cash Equivalents at End of Year	1,293.1				11.3				1,293.1	11.3	13
Great Plains Energy [Member]
Cash Flows from Operating Activities
Net income (loss)									290	213	242.8
Adjustments to reconcile income to net cash from operating activities:
Amortization									30.4	0.8	4.8
Deferred income taxes, net									21.8	(1.7)	(1.4)
Equity in earnings from subsidiaries									(287.5)	(220.9)	(251.1)
Fair value impact of interest rate swaps									(79.3)	0	0
Cash flows affected by changes in:
Accounts receivable from subsidiaries									(9.8)	(0.1)	(3.8)
Taxes receivable									0	0	0.2
Accounts payable to subsidiaries									(20.9)	1.3	(3.2)
Other accounts payable									7	0	0
Accrued taxes									8.4	0.3	4.3
Accrued interest									6	0	(0.1)
Cash dividends from subsidiaries									239	157	144
Uncertain tax positions									(0.4)	0	(2.9)
Other									8.4	8.7	11.8
Net cash from operating activities									213.1	158.4	145.4
Cash Flows from Investing Activities
Purchase of time deposit									(1,000)	0	0
Intercompany lending									0	(1.4)	0
Net money pool lending									3.7	(0.4)	6.1
Investment in subsidiary									(7.3)	(7.8)	(3.6)
Net cash from investing activities									(1,003.6)	(9.6)	2.5
Cash Flows from Financing Activities
Issuance of common stock									1,603.7	3	4.8
Issuance of preference stock									862.5	0	0
Issuance fees									(143.4)	0	(0.1)
Net change in short-term borrowings									(10)	6	(5)
Dividends paid									(194)	(155.5)	(145.6)
Redemption of cumulative preferred stock									(40.1)	0	0
Purchase of treasury stock									(5)	(1.6)	(2.5)
Other financing activities									0.7	(0.7)	0.5
Net cash from financing activities									2,074.4	(148.8)	(147.9)
Net Change in Cash and Cash Equivalents									1,283.9	0	0
Cash and Cash Equivalents at Beginning of Year				$ 0				$ 0	0	0	0
Cash and Cash Equivalents at End of Year	$ 1,283.9				$ 0				$ 1,283.9	$ 0	$ 0

Schedule II Valuation and Quali

Schedule II Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 3.8	$ 2.8	$ 2.5
Additions charged to costs and expenses	9	10.5	11.4
Additions charged to other accounts	8.1	8.7	8.5
Deductions	16.9	18.2	19.6
Balance at end of period	4	3.8	2.8
Allowance for Doubtful Accounts [Member] | Kansas City Power and Light Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	1.8	1.2	1.1
Additions charged to costs and expenses	6.4	7.1	7.6
Additions charged to other accounts	5.5	5.8	5.5
Deductions	11.9	12.3	13
Balance at end of period	1.8	1.8	1.2
Legal Reserve [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	5.9	4.7	4.6
Additions charged to costs and expenses	10.4	2.6	2.7
Additions charged to other accounts	0	0	0
Deductions	0.2	1.4	2.6
Balance at end of period	16.1	5.9	4.7
Legal Reserve [Member] | Kansas City Power and Light Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	5.3	2.9	2.9
Additions charged to costs and expenses	9.8	2.6	2.3
Additions charged to other accounts	0	0	0
Deductions	0	0.2	2.3
Balance at end of period	15.1	5.3	2.9
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	0	0
Additions charged to other accounts	0	0	0
Deductions	0	0	0
Balance at end of period	1.7	1.7	1.7
Reserve for Environmental Costs [Member] | Kansas City Power and Light Company [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
Additions charged to other accounts	0	0	0
Deductions	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	19.9	16.6	20.7
Additions charged to costs and expenses	0.1	4.9	0.5
Additions charged to other accounts	0	0	0
Deductions	3.6	1.6	4.6
Balance at end of period	16.4	19.9	16.6
Valuation Allowance of Deferred Tax Assets [Member] | Kansas City Power and Light Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	0.7	0
Additions charged to costs and expenses	0	0.7
Additions charged to other accounts	0	0
Deductions	0.7	0
Balance at end of period	$ 0	$ 0.7	$ 0