Great Plains Energy (GXP) 10-Q 3 Nov 16 2016 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Oct. 31, 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 Common Stock, Shares Outstanding		215,295,002
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2016

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Current Assets
Cash and cash equivalents	$ 12	$ 11.3
Funds on deposit	2.4	2.1
Receivables, net	194.1	147.7
Accounts receivable pledged as collateral	190	175
Fuel inventories, at average cost	98.6	118.4
Materials and supplies, at average cost	161	155.7
Deferred refueling outage costs	11.7	19.2
Refundable income taxes	1.1	3.8
Prepaid expenses and other assets	67.9	31
Total	738.8	664.2
Utility Plant, at Original Cost
Electric	13,418.7	13,189.9
Less - accumulated depreciation	5,041.6	4,943.7
Net utility plant in service	8,377.1	8,246.2
Construction work in progress	400.9	347.9
Nuclear fuel, net of amortization of $214.9 and $192.5	66.5	68.3
Total	8,844.5	8,662.4
Investments and Other Assets
Nuclear decommissioning trust fund	218.3	200.7
Regulatory assets	980.4	979.1
Goodwill	169	169
Other	93.7	63.2
Total	1,461.4	1,412
Total	11,044.7	10,738.6
Current Liabilities
Notes payable	104	10
Collateralized note payable	190	175
Commercial paper	157.1	224
Current maturities of long-term debt	382.1	1.1
Accounts payable	227.7	352.9
Accrued taxes	123.4	31.6
Accrued interest	61.4	44.7
Accrued compensation and benefits	47.5	41.4
Pension and post-retirement liability	3.4	3.4
Derivative instruments	78.8	0.5
Other	24.7	31.1
Total	1,400.1	915.7
Deferred Credits and Other Liabilities
Deferred income taxes	1,270.5	1,158.8
Deferred tax credits	126.5	125.1
Asset retirement obligations	285	275.9
Pension and post-retirement liability	467.2	455.2
Regulatory liabilities	305.1	284.4
Other	82.6	82.9
Total	2,536.9	2,382.3
Common shareholders' equity
Common stock	2,661.7	2,646.7
Retained earnings	1,092.7	1,024.4
Treasury stock - 128,096 and 101,229 shares, at cost	(3.8)	(2.6)
Accumulated other comprehensive loss	(7.5)	(12)
Total	3,743.1	3,656.5
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	0	39
Long-term debt (Note 11)	3,364.6	3,745.1
Total	7,107.7	7,440.6
Commitments and Contingencies (Note 14)
Total	11,044.7	10,738.6
Preferred Stock 3 Point 80 [Member]
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	0	10
Preferred Stock 4 Point 50 [Member]
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	0	10
Preferred Stock 4 Point 20 [Member]
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	0	7
Preferred Stock 4 Point 35 [Member]
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	0	12
Kansas City Power and Light Company [Member]
Current Assets
Cash and cash equivalents	5.7	2.3
Funds on deposit	1.4	0.5
Receivables, net	168.7	129.2
Related party receivables	91	65.8
Accounts receivable pledged as collateral	110	110
Fuel inventories, at average cost	70.8	83.5
Materials and supplies, at average cost	118.4	114.6
Deferred refueling outage costs	11.7	19.2
Refundable income taxes	0	79
Prepaid expenses and other assets	27.1	27.1
Total	604.8	631.2
Utility Plant, at Original Cost
Electric	9,768.8	9,640.4
Less - accumulated depreciation	3,806.1	3,722.6
Net utility plant in service	5,962.7	5,917.8
Construction work in progress	306.5	246.6
Nuclear fuel, net of amortization of $214.9 and $192.5	66.5	68.3
Total	6,335.7	6,232.7
Investments and Other Assets
Nuclear decommissioning trust fund	218.3	200.7
Regulatory assets	733.6	732.4
Other	20.7	17.6
Total	972.6	950.7
Total	7,913.1	7,814.6
Current Liabilities
Collateralized note payable	110	110
Commercial paper	0	180.3
Current maturities of long-term debt	281	0
Accounts payable	180.3	258.8
Accrued taxes	125.7	25.6
Accrued interest	41.3	32.4
Accrued compensation and benefits	47.5	41.4
Pension and post-retirement liability	2	2
Other	11.5	12.6
Total	799.3	663.1
Deferred Credits and Other Liabilities
Deferred income taxes	1,209.3	1,132.6
Deferred tax credits	123	123.8
Asset retirement obligations	246.7	239.3
Pension and post-retirement liability	445.7	433.4
Regulatory liabilities	176.5	164.6
Other	60.8	61.6
Total	2,262	2,155.3
Common shareholders' equity
Common stock	1,563.1	1,563.1
Retained earnings	1,010.8	879.6
Accumulated other comprehensive loss	(5.6)	(9.6)
Total	2,568.3	2,433.1
Cumulative preferred stock $100 par value
Long-term debt (Note 11)	2,283.5	2,563.1
Total	4,851.8	4,996.2
Commitments and Contingencies (Note 14)
Total	$ 7,913.1	$ 7,814.6

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 214.9	$ 192.5
Common shareholder's equity
Common stock - shares authorized (in shares)	600,000,000	250,000,000
Common stock-shares issued (in shares)	154,925,107	154,504,900
Treasury stock- shares (in shares)	128,096	101,229
Preferred Stock 3 Point 80 [Member]
Cumulative preferred stock
Cumulative preferred stock par value (in dollars per share)	$ 100	$ 100
Cumulative preferred stock, Shares issued (in shares)	0	100,000
Preferred Stock, Dividend Rate, Percentage	3.80%	3.80%
Preferred Stock 4 Point 50 [Member]
Cumulative preferred stock
Cumulative preferred stock par value (in dollars per share)	$ 100	$ 100
Cumulative preferred stock, Shares issued (in shares)	0	100,000
Preferred Stock, Dividend Rate, Percentage	4.50%	4.50%
Preferred Stock 4 Point 20 [Member]
Cumulative preferred stock
Cumulative preferred stock par value (in dollars per share)	$ 100	$ 100
Cumulative preferred stock, Shares issued (in shares)	0	70,000
Preferred Stock, Dividend Rate, Percentage	4.20%	4.20%
Preferred Stock 4 Point 35 [Member]
Cumulative preferred stock
Cumulative preferred stock par value (in dollars per share)	$ 100	$ 100
Cumulative preferred stock, Shares issued (in shares)	0	120,000
Preferred Stock, Dividend Rate, Percentage	4.35%	4.35%
Kansas City Power and Light Company [Member]
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 214.9	$ 192.5
Common shareholder's equity
Common stock - shares authorized (in shares)	1,000	1,000
Common stock-shares issued (in shares)	1	1

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating Revenues
Electric revenues	$ 856.8	$ 781.4	$ 2,099.7	$ 1,939.5
Operating Expenses
Fuel	105.7	124.5	285.7	332
Purchased power	78.4	52.1	176.5	146.3
Transmission	23.8	23.9	64.5	65.1
Utility operating and maintenance expenses	193.3	182.5	553.1	537.4
Costs to achieve the anticipated acquisition of Westar Energy, Inc.	14.4	0	19.4	0
Depreciation and amortization	86.4	82.4	256.9	245.7
General taxes	63.7	58	174.5	162.8
Other	9.2	1.3	15	3.5
Total	574.9	524.7	1,545.6	1,492.8
Operating income	281.9	256.7	554.1	446.7
Non-operating income	4.3	0.9	9.7	9.1
Non-operating expenses	(3)	(1.4)	(10.7)	(8.7)
Interest charges	(67.6)	(51)	(251.7)	(148.3)
Income before income tax expense and income from equity investments	215.6	205.2	301.4	298.8
Income tax expense	(82.7)	(78.6)	(111.5)	(109.6)
Income from equity investments, net of income taxes	0.7	0.2	2.1	0.9
Net income	133.6	126.8	192	190.1
Preferred stock dividend requirements and redemption premium	0.9	0.4	1.7	1.2
Earnings available for common shareholders	$ 132.7	$ 126.4	$ 190.3	$ 188.9
Average number of basic common shares outstanding	154.6	154.2	154.5	154.1
Average number of diluted common shares outstanding	154.9	154.8	154.9	154.8
Basic earnings per common share	$ 0.86	$ 0.82	$ 1.23	$ 1.23
Diluted earnings per common share	0.86	0.82	1.23	1.22
Cash dividends per common share	$ 0.2625	$ 0.245	$ 0.7875	$ 0.735
Comprehensive Income
Net income	$ 133.6	$ 126.8	$ 192	$ 190.1
Other comprehensive income
Reclassification to expenses, net of tax	1.3	1.4	4.1	4.2
Derivative hedging activity, net of tax	1.3	1.4	4.1	4.2
Amortization of net losses included in net periodic benefit costs, net of tax	0.2	0	0.4	0.3
Change in unrecognized pension expense, net of tax	0.2	0	0.4	0.3
Total other comprehensive income	1.5	1.4	4.5	4.5
Comprehensive income	135.1	128.2	196.5	194.6
Kansas City Power and Light Company [Member]
Operating Revenues
Electric revenues	597.6	526.3	1,474.1	1,314.1
Operating Expenses
Fuel	77	89.4	205.6	237.3
Purchased power	41.5	22.9	93.1	73.4
Transmission	14.5	16.2	44.8	42.3
Utility operating and maintenance expenses	131.9	122.9	379.6	365.8
Depreciation and amortization	61.9	58.7	184.1	175
General taxes	51	45.4	136.9	125.1
Other	0.6	0	2.3	(0.2)
Total	378.4	355.5	1,046.4	1,018.7
Operating income	219.2	170.8	427.7	295.4
Non-operating income	3.6	0.6	7.5	6.3
Non-operating expenses	(1.9)	(1.8)	(5.6)	(5.7)
Interest charges	(34.7)	(34.8)	(104.9)	(100.4)
Income before income tax expense and income from equity investments	186.2	134.8	324.7	195.6
Income tax expense	(68.5)	(50.5)	(116.5)	(68.7)
Net income	117.7	84.3	208.2	126.9
Comprehensive Income
Net income	117.7	84.3	208.2	126.9
Other comprehensive income
Reclassification to expenses, net of tax	1.2	1.3	4	4
Derivative hedging activity, net of tax	1.2	1.3	4	4
Total other comprehensive income	1.2	1.3	4	4
Comprehensive income	$ 118.9	$ 85.6	$ 212.2	$ 130.9

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash Flows from Operating Activities
Net income	$ 192	$ 190.1
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	256.9	245.7
Amortization of:
Nuclear fuel	22.4	18.4
Other	52.4	35.3
Deferred income taxes, net	109.9	110.1
Investment tax credit amortization	(1.1)	(1.1)
Income from equity investments, net of income taxes	(2.1)	(0.9)
Fair value impacts of interest rate swaps	78.8	0
Other operating activities (Note 3)	(24.4)	9.7
Net cash from operating activities	684.8	607.3
Cash Flows from Investing Activities
Utility capital expenditures	(435.3)	(520.9)
Allowance for borrowed funds used during construction	(4.7)	(4.3)
Purchases of nuclear decommissioning trust investments	(23.7)	(35.3)
Proceeds from nuclear decommissioning trust investments	21.2	32.8
Other investing activities	(48.7)	(34.5)
Net cash from investing activities	(491.2)	(562.2)
Cash Flows from Financing Activities
Issuance of common stock	2.4	2.3
Issuance of long-term debt	0	348.8
Issuance fees	(68.7)	(2.6)
Repayment of long-term debt	(1.1)	(87)
Net change in short-term borrowings	27.1	(211.2)
Net change in collateralized short-term borrowings	15	19
Dividends paid	(122.5)	(114.6)
Cumulative preferred stock redemption	(40.1)	0
Purchase of treasury stock	(4.9)	(1.6)
Other financing activities	(0.1)	(0.2)
Net cash from financing activities	(192.9)	(47.1)
Net Change in Cash and Cash Equivalents	0.7	(2)
Cash and Cash Equivalents at Beginning of Year	11.3	13
Cash and Cash Equivalents at End of Period	12	11
Kansas City Power and Light Company [Member]
Cash Flows from Operating Activities
Net income	208.2	126.9
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	184.1	175
Amortization of:
Nuclear fuel	22.4	18.4
Other	25.6	20.8
Deferred income taxes, net	74	19.8
Investment tax credit amortization	(0.8)	(0.7)
Other operating activities (Note 3)	74.7	103.6
Net cash from operating activities	588.2	463.8
Cash Flows from Investing Activities
Utility capital expenditures	(286.1)	(410.2)
Allowance for borrowed funds used during construction	(3.8)	(3)
Purchases of nuclear decommissioning trust investments	(23.7)	(35.3)
Proceeds from nuclear decommissioning trust investments	21.2	32.8
Net money pool lending	(11.1)	0
Other investing activities	(23.8)	(19.7)
Net cash from investing activities	(327.3)	(435.4)
Cash Flows from Financing Activities
Issuance of long-term debt	0	348.8
Issuance fees	(0.2)	(2.6)
Repayment of long-term debt	0	(85.9)
Net change in short-term borrowings	(180.3)	(276.2)
Net money pool borrowings	0	(12.6)
Dividends paid	(77)	0
Net cash from financing activities	(257.5)	(28.5)
Net Change in Cash and Cash Equivalents	3.4	(0.1)
Cash and Cash Equivalents at Beginning of Year	2.3	2.7
Cash and Cash Equivalents at End of Period	$ 5.7	$ 2.6

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]	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, 2014			$ 2,639.3	$ 1,563.1	$ 967.8	$ 726.8	$ (2.3)	$ (18.7)	$ (14.9)
Beginning balance (in shares) at Dec. 31, 2014			154,254,037	1
Beginning balance, treasury stock (in shares) at Dec. 31, 2014							(91,281)
Issuance of common stock			$ 5.5
Issuance of common stock (in shares)			210,579
Equity compensation expense, net of forfeitures			$ 1.4
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.4)
Forfeiture of restricted common stock			0.4
Compensation expense recognized			1.3
Other			(0.5)
Net income	$ 190.1	$ 126.9			190.1	126.9
Redemption premium on preferred stock					0
Dividends:
Common stock ($0.7875 and $0.735 per share)					(113.4)	0
Preferred stock - at required rates					(1.2)
Performance shares					(0.6)
Treasury shares acquired							$ (1.9)
Treasury shares acquired (in shares)							(73,326)
Treasury shares reissued							$ 1.6
Treasury shares reissued (in shares)							64,180
Derivative hedging activity, net of tax	4.2	4						4.2	4
Change in unrecognized pension expense, net of tax	0.3							0.3
Ending balance at Sep. 30, 2015	3,670.9	2,405.9	$ 2,645	$ 1,563.1	1,042.7	853.7	$ (2.6)	(14.2)	(10.9)
Ending balance, treasury stock (in shares) at Sep. 30, 2015							(100,427)
Ending balance (in shares) at Sep. 30, 2015			154,464,616	1
Beginning balance at Dec. 31, 2015	$ 3,656.5	2,433.1	$ 2,646.7	$ 1,563.1	1,024.4	879.6	$ (2.6)	(12)	(9.6)
Beginning balance (in shares) at Dec. 31, 2015			154,504,900	1
Beginning balance, treasury stock (in shares) at Dec. 31, 2015	(101,229)						(101,229)
Issuance of common stock			$ 12.5
Issuance of common stock (in shares)			420,207
Equity compensation expense, net of forfeitures			$ 3.1
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.8)
Forfeiture of restricted common stock			0
Compensation expense recognized			2
Other			0.2
Net income	$ 192	208.2			192	208.2
Redemption premium on preferred stock					(0.6)
Dividends:
Common stock ($0.7875 and $0.735 per share)					(121.8)	(77)
Preferred stock - at required rates					(0.7)
Performance shares					(0.6)
Treasury shares acquired							$ (4.1)
Treasury shares acquired (in shares)							(136,562)
Treasury shares reissued							$ 2.9
Treasury shares reissued (in shares)							109,695
Derivative hedging activity, net of tax	4.1	4						4.1	4
Change in unrecognized pension expense, net of tax	0.4							0.4
Ending balance at Sep. 30, 2016	$ 3,743.1	$ 2,568.3	$ 2,661.7	$ 1,563.1	$ 1,092.7	$ 1,010.8	$ (3.8)	$ (7.5)	$ (5.6)
Ending balance, treasury stock (in shares) at Sep. 30, 2016	(128,096)						(128,096)
Ending balance (in shares) at Sep. 30, 2016			154,925,107	1

Consolidated Statements of Com7

Consolidated Statements of Common Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stock Transactions, Parenthetical Disclosures [Abstract]
Common Stock, Dividends, Per Share, Declared	$ 0.2625	$ 0.245	$ 0.7875	$ 0.735

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 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. 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 21 for additional information. 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. The effect of dilutive securities, calculated using the treasury stock method, assumes the issuance of common shares applicable to performance shares and restricted stock. The following table reconciles Great Plains Energy's basic and diluted EPS. Three Months Ended September 30 Year to Date 2016 2015 2016 2015 Income (millions, except per share amounts) Net income $ 133.6 $ 126.8 $ 192.0 $ 190.1 Less: preferred stock dividend requirements and redemption premium 0.9 0.4 1.7 1.2 Earnings available for common shareholders $ 132.7 $ 126.4 $ 190.3 $ 188.9 Common Shares Outstanding Average number of common shares outstanding 154.6 154.2 154.5 154.1 Add: effect of dilutive securities 0.3 0.6 0.4 0.7 Diluted average number of common shares outstanding 154.9 154.8 154.9 154.8 Basic EPS $ 0.86 $ 0.82 $ 1.23 $ 1.23 Diluted EPS $ 0.86 $ 0.82 $ 1.23 $ 1.22 There were no anti-dilutive shares excluded from the computation of dilutive EPS for the three months ended and year to date September 30, 2016, and 2015. Dividends Declared In November 2016 , Great Plains Energy's Board of Directors (Great Plains Energy Board) declared a quarterly dividend of $0.2750 per share on Great Plains Energy's common stock. The common dividend is payable December 20, 2016 , to shareholders of record as of November 29, 2016 . The Great Plains Energy Board also declared a regular quarterly dividend on Great Plains Energy's newly issued 7.00% Series B Mandatory Convertible Preferred Stock (Series B Preferred Stock). The dividend will be payable December 15, 2016 , to shareholders of record as of December 1, 2016 . See Note 13 for additional information regarding the Series B Preferred Stock. In November 2016 , KCP&L's Board of Directors declared a cash dividend payable to Great Plains Energy of $45 million payable on December 19, 2016 . 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 Generally Accepted Accounting Principles (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 are evaluating the effect that ASU No. 2014-09 will have on their consolidated financial statements and related disclosures and have not yet selected a transition method nor have they determined the effect of the standard on their ongoing financial reporting. 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 plan to adopt ASU No. 2016-09 effective January 1, 2017 and it is not expected to have a significant impact on their ongoing financial reporting.

Anticipated Acquisition of West

Anticipated Acquisition of Westar Energy, Inc.	9 Months Ended
	Sep. 30, 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 10 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 13 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 the underwriting discount). 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 $836.6 million after the underwriting discount). See Note 13 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 Nuclear Regulatory Commission (NRC), The Federal Energy Regulatory Commission (FERC) and The Federal Communications Commission (FCC); as well as other customary conditions. MPSC Jurisdiction Great Plains Energy believes that the Public Service Commission of the State of Missouri (MPSC) does not have jurisdiction to approve or disapprove the anticipated acquisition of Westar. In October 2016, the Midwest Energy Consumers Group (MECG) filed a complaint with the MPSC in which MECG asserted that MPSC approval was necessary in order for Great Plains Energy to acquire Westar and the MPSC subsequently issued an order requesting that a procedural schedule be established that would include an evidentiary hearing, oral argument, or both, on the issue of MPSC jurisdiction. The MPSC order required that the evidentiary hearing or oral argument occur no later than December 2016. If the MPSC ultimately decides to exercise its jurisdiction, Great Plains Energy could be required to file an application with the MPSC to approve the anticipated acquisition of Westar. In October 2016, Great Plains Energy 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. Great Plains Energy and the MPSC staff have requested that the MPSC approve their stipulation and agreement by November 30, 2016. 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. Accordingly, a decision from KCC on this joint application is expected by April 2017. In October 2016, KCC issued an order addressing KCC's merger standards and whether the joint application is in conformity with these standards. The order allows certain intervenors to file for appropriate relief if they believe the joint application does not adequately address KCC's merger standards. If relief is requested and approved by KCC, the current joint application could be dismissed and Great Plains Energy, KCP&L and Westar could be required to file a new joint application. Great Plains Energy, KCP&L and Westar believe the current joint application is in conformity with KCC's merger standards but out of an abundance of caution, filed a motion with KCC in November 2016 requesting to provide supplemental testimony to address KCC's October 2016 order. 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. 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 . Shareholder Lawsuits Following the announcement of the Merger Agreement, two putative class action complaints (which were subsequently consolidated) (Consolidated Putative Class Action) and a derivative complaint (Derivative Action) on behalf of nominal defendant Westar challenging the merger were filed in the District Court of Shawnee County, Kansas. A separate putative class action complaint (Missouri Action) was filed in the Circuit Court of Jackson County, Missouri, at Kansas City, Sixteenth Judicial District on behalf of a putative class of Great Plains Energy shareholders. The complaint in the Consolidated Putative Class Action names as defendants Westar, the members of the Westar Board and Great Plains Energy. The complaint in the Missouri Action names as defendants Great Plains Energy and the members of the Great Plains Energy Board. The complaint in the Derivative Action names as defendants the members of the Westar Board and Great Plains Energy, with Westar named as a nominal defendant. The complaint in the Consolidated Putative Class Action asserts that the members of the Westar Board breached their fiduciary duties to Westar shareholders in connection with the proposed merger, including the duty of candor, and that Westar and Great Plains Energy aided and abetted such breaches of fiduciary duties. The complaint in the Derivative Action asserts breach of fiduciary duty claims against members of the Westar Board, and aiding and abetting claims against Great Plains Energy, on behalf of nominal defendant Westar. The complaint in the Missouri Action asserts that the members of the Great Plains Energy Board breached their fiduciary duty of candor in connection with the proposed merger by allegedly failing to disclose certain facts in the Company's preliminary Form S-4. Among other remedies, the plaintiffs in each case seek to enjoin the merger, in addition to reimbursement of costs. In September 2016, the plaintiff in the Missouri Action agreed to withdraw its motion for a preliminary injunction and in exchange, Great Plains Energy made additional supplemental disclosures to the Proxy Statement/Prospectus. This agreement does not release or otherwise prejudice any potential claims of any member of the putative class and does not constitute any admission by any of the defendants as to the merits of any claims. In September 2016, the parties in the Consolidated Putative Class Action and the Derivative Action independently agreed to withdraw requests for injunctive relief and otherwise agreed in principle to dismissing the actions with prejudice and to providing releases. In exchange, the parties in the Derivative Action agreed, and Westar made, supplemental disclosures to the Proxy Statement/Prospectus and the parties in the Consolidated Putative Class Action agreed, and Westar: (i) made supplemental disclosures and (ii) granted waivers of the prohibition on requesting a waiver of the standstill provisions in the confidentiality and standstill agreements executed by the bidders that participated in the Westar sale process. Because Great Plains Energy is a defendant in the Consolidated Putative Class Action and the Derivative Action and is a party to these agreements, Great Plains Energy also made the same supplemental disclosures that Westar made. These agreements do not constitute any admission by any of the defendants as to the merits of any claims.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2016
Supplemental Cash Flow Elements [Abstract]
Cash Flow, Supplemental Disclosures [Text Block]	3. SUPPLEMENTAL CASH FLOW INFORMATION Great Plains Energy Other Operating Activities Year to Date September 30 2016 2015 Cash flows affected by changes in: (millions) Receivables $ (45.9 ) $ (13.2 ) Accounts receivable pledged as collateral (15.0 ) (19.0 ) Fuel inventories 19.8 (10.8 ) Materials and supplies (5.3 ) (2.9 ) Accounts payable (119.8 ) (121.9 ) Accrued taxes 97.2 89.2 Accrued interest 16.7 16.9 Deferred refueling outage costs 7.5 (12.8 ) Pension and post-retirement benefit obligations 53.2 48.8 Allowance for equity funds used during construction (4.3 ) (3.8 ) Fuel recovery mechanisms (16.8 ) 36.6 Other (11.7 ) 2.6 Total other operating activities $ (24.4 ) $ 9.7 Cash paid during the period: Interest $ 130.2 $ 121.2 Income taxes $ 0.2 $ 0.2 Non-cash investing activities: Liabilities accrued for capital expenditures $ 30.7 $ 23.4 KCP&L Other Operating Activities Year to Date September 30 2016 2015 Cash flows affected by changes in: (millions) Receivables $ (53.5 ) $ (6.2 ) Fuel inventories 12.7 (11.6 ) Materials and supplies (3.8 ) (4.0 ) Accounts payable (80.3 ) (83.1 ) Accrued taxes 179.3 162.3 Accrued interest 8.9 12.3 Deferred refueling outage costs 7.5 (12.8 ) Pension and post-retirement benefit obligations 53.7 48.8 Allowance for equity funds used during construction (4.0 ) (2.9 ) Fuel recovery mechanisms (31.0 ) 1.8 Other (14.8 ) (1.0 ) Total other operating activities $ 74.7 $ 103.6 Cash paid during the period: Interest $ 86.7 $ 79.1 Non-cash investing activities: Liabilities accrued for capital expenditures $ 25.7 $ 15.7

Receivables

Receivables	9 Months Ended
	Sep. 30, 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. September 30 December 31 2016 2015 Great Plains Energy (millions) Customer accounts receivable - billed $ 55.3 $ 3.4 Customer accounts receivable - unbilled 89.3 71.6 Allowance for doubtful accounts - customer accounts receivable (5.1 ) (3.8 ) Other receivables 54.6 76.5 Total $ 194.1 $ 147.7 KCP&L Customer accounts receivable - billed $ 54.9 $ 2.8 Customer accounts receivable - unbilled 70.8 58.8 Allowance for doubtful accounts - customer accounts receivable (2.7 ) (1.8 ) Other receivables 45.7 69.4 Total $ 168.7 $ 129.2 Great Plains Energy's and KCP&L's other receivables at September 30, 2016 , and December 31, 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 September 30, 2016 , and December 31, 2015 , Great Plains Energy's accounts receivable pledged as collateral and the corresponding short-term collateralized note payable were $190.0 million and $175.0 million , respectively. At September 30, 2016 , and December 31, 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	9 Months Ended
	Sep. 30, 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 reexamined its 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. 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 Decommissioning Trust Fund The following table summarizes the change in Great Plains Energy's and KCP&L's nuclear decommissioning trust fund. September 30 December 31 Decommissioning Trust (millions) Beginning balance January 1 $ 200.7 $ 199.0 Contributions 2.5 3.3 Earned income, net of fees 3.0 3.4 Net realized gains 0.2 0.7 Net unrealized gains (losses) 11.9 (5.7 ) Ending balance $ 218.3 $ 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. September 30, 2016 December 31, 2015 Cost Basis Unrealized Gains Unrealized Losses Fair Value Cost Basis Unrealized Gains Unrealized Losses Fair Value (millions) Equity securities $ 92.4 $ 56.2 $ (1.2 ) $ 147.4 $ 89.6 $ 47.9 $ (2.1 ) $ 135.4 Debt securities 64.5 4.8 — 69.3 59.6 2.6 (0.5 ) 61.7 Other 1.6 — — 1.6 3.6 — — 3.6 Total $ 158.5 $ 61.0 $ (1.2 ) $ 218.3 $ 152.8 $ 50.5 $ (2.6 ) $ 200.7 The weighted average maturity of debt securities held by the trust at September 30, 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. Three Months Ended Year to Date 2016 2015 2016 2015 (millions) Realized gains $ 0.6 $ 0.6 $ 1.5 $ 3.2 Realized losses (0.3 ) (0.5 ) (1.3 ) (2.3 )

Regulatory Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 2016
Regulated Operations [Abstract]
Regulatory Matters	6 . REGULATORY MATTERS 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. An evidentiary hearing is scheduled to occur in February 2017. New rates are expected 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 will take effect no later than December 22, 2016. KCP&L Kansas 2015 Rate Case Proceedings In September 2015, KCC issued an order for KCP&L authorizing an increase in annual revenues of $48.7 million , a return on equity of 9.3% and a rate-making equity ratio of 50.48% . KCP&L filed a Petition for Judicial Review with the Court of Appeals of Kansas in November 2015 regarding various issues, which was denied in March 2016. The rates established by the order took effect on October 1, 2015. KCP&L Missouri 2015 Rate Case Proceedings In September 2015, the MPSC issued an order for KCP&L authorizing an increase in annual revenues of $89.7 million , a return on equity of 9.5% and a rate-making equity ratio of approximately 50.09% . The MPSC also approved KCP&L's request to implement a Fuel Adjustment Clause. The rates established by the order took effect on September 29, 2015, and are effective unless and until modified by the MPSC or stayed by a court. Notices of Appeal of the September 2015 MPSC order were filed with the Missouri Court of Appeals, Western District (Court of Appeals), by KCP&L in October 2015 and by MECG in November 2015 regarding various issues. In September 2016, the Court of Appeals upheld the September 2015 MPSC order in all respects. KCP&L and MECG have filed Motions for Rehearing and Applications for Transfer to the Supreme Court of Missouri with the Court of Appeals.

Goodwill

Goodwill	9 Months Ended
	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets [Text Block]	7. GOODWILL 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. 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.

Pension Plans and Other Employe

Pension Plans and Other Employee Benefits	9 Months Ended
	Sep. 30, 2016
Compensation and Retirement Disclosure [Abstract]
Pension Plans and Other Employee Benefits	8. 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; however, for union employees hired after October 1, 2013, the benefits are derived from a cash balance account formula. Effective in 2014, the 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. The following tables provide Great Plains Energy's components of net periodic benefit costs prior to the effects of capitalization and sharing with joint owners of power plants. Pension Benefits Other Benefits Three Months Ended September 30 2016 2015 2016 2015 Components of net periodic benefit costs (millions) Service cost $ 10.5 $ 11.4 $ 0.7 $ 0.8 Interest cost 13.2 12.5 1.5 1.7 Expected return on plan assets (12.3 ) (13.0 ) (0.8 ) (0.7 ) Prior service cost 0.2 0.2 0.3 0.7 Recognized net actuarial (gain)/loss 13.0 12.9 (0.3 ) 0.1 Transition obligation — — — 0.1 Net periodic benefit costs before regulatory adjustment 24.6 24.0 1.4 2.7 Regulatory adjustment (1.1 ) (3.5 ) 1.4 1.4 Net periodic benefit costs $ 23.5 $ 20.5 $ 2.8 $ 4.1 Pension Benefits Other Benefits Year to Date September 30 2016 2015 2016 2015 Components of net periodic benefit costs (millions) Service cost $ 31.5 $ 34.0 $ 2.0 $ 2.5 Interest cost 39.7 37.7 4.6 5.1 Expected return on plan assets (36.9 ) (38.8 ) (2.3 ) (2.2 ) Prior service cost 0.5 0.6 0.9 2.3 Recognized net actuarial (gain)/loss 38.9 38.5 (1.1 ) 0.2 Transition obligation — — — 0.1 Net periodic benefit costs before regulatory adjustment 73.7 72.0 4.1 8.0 Regulatory adjustment (3.1 ) (9.3 ) 4.4 4.2 Net periodic benefit costs $ 70.6 $ 62.7 $ 8.5 $ 12.2 Year to date September 30, 2016 , Great Plains Energy contributed $23.6 million to the pension plans and expects to contribute an additional $52.4 million in 2016 to satisfy the Employee Retirement Income Security Act of 1974, as amended (ERISA) funding requirements and the MPSC and KCC rate orders, the majority of which is expected to be paid by KCP&L. Also in 2016 , Great Plains Energy expects to make contributions of $5.1 million to the post-retirement benefit plans, the majority of which is expected to be paid by KCP&L.

Equity Compensation

Equity Compensation	9 Months Ended
	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Compensation	9. 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. 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. Three Months Ended September 30 Year to Date September 30 2016 2015 2016 2015 Great Plains Energy (millions) Equity compensation expense $ 0.4 $ 3.7 $ 3.9 $ 4.6 Income tax benefit — 1.4 1.3 1.7 KCP&L Equity compensation expense $ 0.2 $ 2.5 $ 2.5 $ 3.1 Income tax benefit — 0.9 0.8 1.1 Performance Shares Performance share activity year to date September 30, 2016, 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 September 30, 2016 625,100 28.13 * weighted-average At September 30, 2016 , the remaining weighted-average contractual term was 1.4 years. There were no shares granted for the three months ended September 30, 2016. The weighted-average grant-date fair value of shares granted was $31.41 year to date September 30, 2016. The weighted-average grant-date fair value of shares granted was $22.46 and $24.03 for the three months ended and year to date September 30, 2015 , respectively. At September 30, 2016 , there was $7.7 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 and $0.5 million year to date September 30, 2016 , and 2015 , respectively. 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. Restricted Stock Restricted stock activity year to date September 30, 2016, 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 (73,417 ) 22.69 Forfeited (572 ) 27.51 Ending balance September 30, 2016 253,572 27.13 * weighted-average At September 30, 2016 , the remaining weighted-average contractual term was 1.3 years. There were no shares granted for the three months ended September 30, 2016. The weighted-average grant-date fair value of shares granted was $29.41 year to date September 30, 2016. The weighted-average grant-date fair value of shares granted was $24.20 and $25.88 for the three months ended and year to date September 30, 2015, respectively. At September 30, 2016 , there was $3.2 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 $0.1 million and $1.7 million for the three months ended and year to date September 30, 2016, respectively. Total fair value of shares vested was $0.1 million and $2.1 million for the three months ended and year to date September 30, 2015 , respectively.

Short-term Borrowings and Short

Short-term Borrowings and Short-term Bank Lines of Credit	9 Months Ended
	Sep. 30, 2016
Short-term Borrowings and Short-term Bank Lines of Credit [Abstract]
Short-term Borrowings and Short-term Bank Lines of Credit [Text Block]	10 . 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 September 30, 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 September 30, 2016 , Great Plains Energy had $104.0 million of outstanding cash borrowings at a weighted-average interest rate of 2.06% and had issued $0.2 million 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 September 30, 2016 , KCP&L was in compliance with this covenant. At September 30, 2016 , KCP&L had no commercial paper outstanding, 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 September 30, 2016 , GMO was in compliance with this covenant. At September 30, 2016 , GMO had $157.1 million of commercial paper outstanding at a weighted-average interest rate of 0.71% , had issued letters of credit totaling $2.1 million and had no outstanding cash borrowings under the credit facility. At December 31, 2015 , GMO had $43.7 million 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 November 3, 2016, the aggregate principal amount of the facility was $5.1 billion .

Long-Term Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2016
Debt Disclosure [Abstract]
Long-Term Debt	11. LONG-TERM DEBT Great Plains Energy's and KCP&L's long-term debt is detailed in the following table. September 30 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 0.76% 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 (15.9 ) (17.3 ) Total KCP&L excluding current maturities (d) 2,283.5 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 (1.9 ) (2.1 ) Total Great Plains Energy excluding current maturities (d) $ 3,364.6 $ 3,745.1 (a) Weighted-average interest rates at September 30, 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 September 30, 2016, and December 31, 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

Common Shareholders' Equity

Common Shareholders' Equity	9 Months Ended
	Sep. 30, 2016
Stockholders' Equity Note [Abstract]
Common Shareholders' Equity	12. COMMON SHAREHOLDERS' EQUITY 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, the 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 underwriting discount). Great Plains Energy plans to use proceeds from the offering to finance a portion of the cash consideration for the anticipated acquisition of Westar.

Preferred Stock

Preferred Stock	9 Months Ended
	Sep. 30, 2016
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock [Text Block]	13 . PREFERRED STOCK 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. 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 preferred stock of Great Plains Energy designated as 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 $836.6 million after underwriting discount). Great Plains Energy plans to use proceeds from the offering to finance 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.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	14 . 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 Allowance for Funds Used During Construction (AFUDC) and property taxes) over the next five years to comply with environmental regulations are in the following table. The total cost of compliance with any existing, proposed or future laws and regulations may be significantly different from these cost estimates provided. 2016 2017 2018 2019 2020 (millions) Great Plains Energy $ 99.6 $ 45.5 $ 20.6 $ 98.9 $ 151.9 KCP&L 83.8 30.1 14.4 87.3 130.0 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. Mercury and Air Toxics Standards (MATS) Rule In December 2011, the EPA finalized the MATS Rule that will reduce emissions of toxic air pollutants, also known as hazardous air pollutants, from new and existing coal- and oil-fired electric utility generating units with a capacity of greater than 25 MWs. The rule establishes numerical emission limits for mercury, particulate matter (a surrogate for non-mercury metals) and hydrochloric acid (a surrogate for acid gases). The rule establishes work practices, instead of numerical emission limits, for organic air toxics, including dioxin/furan. KCP&L's and GMO's affected coal-fired units currently comply with the rule. Industrial Boiler Rule In December 2012, the EPA issued a final rule that would reduce emissions of hazardous air pollutants from new and existing industrial boilers. The final rule establishes numeric emission limits for mercury, particulate matter (as a surrogate for non-mercury metals), hydrogen chloride (as a surrogate for acid gases) and carbon monoxide (as a surrogate for non-dioxin organic hazardous air pollutants). The final rule establishes emission limits for KCP&L's and GMO's existing units that produce steam other than for the generation of electricity. The final rule does not apply to KCP&L's and GMO's electricity generating boilers, but would apply to most of GMO's Lake Road boilers, which also serve steam customers, and to auxiliary boilers at other generating facilities. KCP&L's and GMO's affected units currently comply with the rule. 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 21 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 will be 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 did 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. The Companies are subject to existing renewable energy standards in Missouri. Management believes that national renewable energy standards are also possible. The timing, provisions and impact of such possible future requirements, including the cost to obtain and install new equipment to achieve compliance, cannot be reasonably estimated at this time. 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 coal combustion residuals (CCRs) under the Resource Conservation and Recovery Act (RCRA) subtitle D to address the risks from the disposal of CCRs generated from the combustion of coal at electric generating facilities. The Companies use coal in generating electricity and dispose of the CCRs in both on-site facilities and facilities owned by third parties. KCP&L's Iatan, La Cygne, and Montrose Stations and GMO's Sibley Station have on-site facilities affected by the rule. The rule requires periodic assessments; groundwater monitoring; location restrictions; design and operating requirements; recordkeeping and notifications; and closure, among other requirements, for CCR units. The rule was promulgated in the Federal Register on April 17, 2015, and became effective six months after promulgation with various obligations effective at specified times within the rule. Estimated capital costs to comply with the CCR rule are included in the estimated capital expenditures table above. Certain requirements of the rule would require Great Plains Energy or KCP&L to expedite or incur additional capital expenditures in the future. Great Plains Energy and KCP&L have Asset Retirement Obligations (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 September 30, 2016 , and December 31, 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 September 30, 2016 , and December 31, 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.

Legal Proceedings

Legal Proceedings	9 Months Ended
	Sep. 30, 2016
Legal Proceedings [Abstract]
Contingencies Disclosure [Text Block]	15. 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 December 2001, various parties appealed FERC orders to the United States Court of Appeals for the Ninth Circuit (Ninth Circuit) seeking review of a number of issues, including expansion of the refund period to include periods prior to October 2, 2000 (the Summer Period). MPS Merchant was a net seller of power during the Summer Period. On August 2, 2006, the Ninth Circuit issued an order finding, among other things, that FERC erred in failing to consider certain legal issues regarding whether it has authority to order refunds for violation of FERC-approved tariffs during the Summer Period. The court remanded the matter to FERC for further consideration. In November 2014, FERC issued an order finding that MPS Merchant engaged in tariff violations during the Summer Period and ordering 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 on rehearing, confirming its findings of violation and expanding the remedy from its November 2014 order to cover additional MPS Merchant sales in the California markets. MPS Merchant filed another request for rehearing, challenging the expanded remedy, and also filed a petition for review of the November 2014 and November 2015 orders with the Ninth Circuit. In February 2016, FERC issued another order on rehearing/clarification that requires MPS Merchant to refund, in the form of disgorgement, 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. That order is subject to further rehearing and judicial review. Under FERC's orders, MPS Merchant may be able to offset its costs of selling power against any remedy ultimately imposed to ensure that it does not under-recover its actual costs. In September 2016, the Ninth Circuit denied MPS Merchant's petition for review regarding liability for tariff violations, but declined to address the issue of remedy as the FERC remedial order is not final. 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 cash and other consideration. The agreement is subject to approval by FERC. As a result of this agreement, Great Plains Energy has accrued an insignificant amount of loss in its consolidated financial statements as of September 30, 2016.

Related Party Transactions and

Related Party Transactions and Relationships	9 Months Ended
	Sep. 30, 2016
Related Party Transactions [Abstract]
Related Party Transactions and Relationships	16 . 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 $48.9 million and $143.8 million , respectively, for the three months ended and year to date September 30, 2016. These cost totaled $45.5 million and $137.7 million , respectively, for the three months ended and year to date September 30, 2015. KCP&L and GMO are also authorized to participate in the Great Plains Energy money pool, an internal financing arrangement in which funds may be lent on a short-term basis to KCP&L and GMO from Great Plains Energy and between KCP&L and GMO. At September 30, 2016, KCP&L had a money pool receivable from GMO of $11.1 million . At December 31, 2015, KCP&L had no outstanding receivables or payables under the money pool. The following table summarizes KCP&L's related party net receivables. September 30 December 31 2016 2015 (millions) Net receivable from GMO $ 71.5 $ 50.0 Net receivable from Great Plains Energy 19.5 15.8

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	17 . 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, 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 normal purchases and normal sales (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. Great Plains Energy and KCP&L have posted collateral, in the ordinary course of business, for the aggregate fair value of all derivative instruments with credit risk-related contingent features that are in a liability position. At September 30, 2016 , Great Plains Energy and KCP&L have posted collateral in excess of the aggregate fair value of their derivative instruments; therefore, if the credit risk-related contingent features underlying these agreements were triggered, Great Plains Energy and KCP&L would not be required to post additional collateral to their counterparties. 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's risk management policy uses derivative instruments to mitigate exposure to commodity market price fluctuations. At September 30, 2016, KCP&L had financial contracts in place to hedge approximately 20% and 7% of the expected summer month natural gas generation for Missouri jurisdictional retail sales for 2017 and 2018, respectively. KCP&L has designated these financial contracts 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 the MPSC. Recovery of actual costs will not impact earnings, but will impact cash flows due to the timing of the recovery mechanism. 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. GMO's risk management policy uses derivative instruments to mitigate price exposure to natural gas price volatility in the market. At September 30, 2016 , GMO had financial contracts in place to hedge approximately 66% , 37% and 12% of the expected on-peak natural gas generation and natural gas equivalent purchased power price exposure for the remainder of 2016 , 2017 and 2018 , respectively. The fair value of the portfolio will settle against actual purchases of natural gas and purchased power. GMO has designated its natural gas hedges as economic hedges (non-hedging derivatives). In connection with GMO's 2005 Missouri electric rate case, it was agreed that the settlement costs of these contracts would be recognized in fuel expense. The settlement cost is included in a recovery mechanism. A regulatory asset or liability is recorded to reflect the change in the timing of recognition authorized by the 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. September 30 December 31 2016 2015 Notional Contract Amount Fair Value Notional Contract Amount Fair Value Great Plains Energy (millions) Non-hedging derivatives Futures contracts $ 14.9 $ — $ 26.6 $ (5.7 ) Forward contracts 11.1 2.6 15.6 3.1 Transmission congestion rights 5.1 0.7 5.6 (0.5 ) Interest rate swaps 4,415.0 (78.8 ) — — KCP&L Non-hedging derivatives Futures contracts $ 0.2 $ — $ 0.9 $ (0.1 ) Transmission congestion rights 3.9 0.4 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 September 30, 2016 Classification Fair Value Fair Value Derivatives Not Designated as Hedging Instruments (millions) Commodity contracts Other $ 5.3 $ 2.0 Interest rate contracts Derivative instruments — 78.8 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 September 30, 2016 Classification Fair Value Fair Value Derivatives Not Designated as Hedging Instruments (millions) Commodity contracts Other $ 1.1 $ 0.7 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 September 30, 2016 (millions) Derivative assets $ 5.3 $ (2.0 ) $ 3.3 $ — $ — $ 3.3 Derivative liabilities 80.8 (2.0 ) 78.8 — — 78.8 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 September 30, 2016 (millions) Derivative assets $ 1.1 $ (0.7 ) $ 0.4 $ — $ — $ 0.4 Derivative liabilities 0.7 (0.7 ) — — — — December 31, 2015 Derivative assets $ 0.2 $ (0.2 ) $ — $ — $ — $ — Derivative liabilities 0.7 (0.3 ) 0.4 — — 0.4 At September 30, 2016 , and December 31, 2015 , Great Plains Energy offset $0.1 million and $5.7 million , respectively, of cash collateral posted with counterparties against net derivative positions. See Note 19 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 September 30, 2016 , includes $8.9 million that is expected to be reclassified to expenses over the next twelve months. KCP&L's accumulated OCI at September 30, 2016 , includes $8.5 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 Three Months Ended September 30 Year to Date Derivatives Not Designated as Hedging Instruments 2016 2015 2016 2015 Location of Gain (Loss) (millions) Electric revenues $ 2.0 $ (0.2 ) $ 1.7 $ (7.9 ) Fuel (0.1 ) (0.1 ) (4.6 ) (1.2 ) Purchased power 0.5 (0.2 ) 0.2 (1.4 ) Interest charges (1.8 ) — (78.8 ) — Regulatory asset — (1.9 ) (0.1 ) (5.1 ) Regulatory liability (0.3 ) — 0.9 — Total $ 0.3 $ (2.4 ) $ (80.7 ) $ (15.6 ) KCP&L Three Months Ended September 30 Year to Date Derivatives Not Designated as Hedging Instruments 2016 2015 2016 2015 Location of Gain (Loss) (millions) Electric revenues $ 2.0 $ (0.2 ) $ 1.7 $ (7.9 ) Fuel 0.3 1.1 0.2 1.3 Regulatory asset 0.1 (0.1 ) — (0.1 ) Regulatory liability — — 0.5 — Total $ 2.4 $ 0.8 $ 2.4 $ (6.7 )

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	18. 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 September 30, 2016 , the book value and fair value of Great Plains Energy's long-term debt, including current maturities, were $3.8 billion and $4.1 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 September 30, 2016 , and 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 September 30 Level 1 Level 2 Level 3 KCP&L (millions) Assets Nuclear decommissioning trust (a) Equity securities $ 147.4 $ 147.4 $ — $ — Debt securities U.S. Treasury 29.7 29.7 — — U.S. Agency 1.8 — 1.8 — State and local obligations 3.1 — 3.1 — Corporate bonds 34.4 — 34.4 — Foreign governments 0.3 — 0.3 — Cash equivalents 1.6 1.6 — — Total nuclear decommissioning trust 218.3 178.7 39.6 — Self-insured health plan trust (b) Equity securities 0.9 0.9 — — Debt securities 4.8 — 4.8 — Cash and cash equivalents 8.0 8.0 — — Total self-insured health plan trust 13.7 8.9 4.8 — Derivative instruments - commodity (c) 1.1 — — 1.1 Total $ 233.1 $ 187.6 $ 44.4 $ 1.1 Liabilities Derivative instruments - commodity (c) 0.7 — — 0.7 Total $ 0.7 $ — $ — $ 0.7 Other Great Plains Energy Assets Derivative instruments - commodity (c) $ 4.2 $ 1.1 $ 2.3 $ 0.8 SERP rabbi trusts (d) Equity securities 0.1 0.1 — — Total $ 4.3 $ 1.2 $ 2.3 $ 0.8 Liabilities Derivative instruments Commodity (c) $ 1.3 $ 1.1 $ — $ 0.2 Interest rates (e) 78.8 — — 78.8 Total derivative instruments 80.1 1.1 — 79.0 Total $ 80.1 $ 1.1 $ — $ 79.0 Great Plains Energy Assets Nuclear decommissioning trust (a) $ 218.3 $ 178.7 $ 39.6 $ — Self-insured health plan trust (b) 13.7 8.9 4.8 — Derivative instruments (c) 5.3 1.1 2.3 1.9 SERP rabbi trusts (d) 0.1 0.1 — — Total $ 237.4 $ 188.8 $ 46.7 $ 1.9 Liabilities Derivative instruments (c) (e) 80.8 1.1 — 79.7 Total $ 80.8 $ 1.1 $ — $ 79.7 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 (d) 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 (d) 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 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) At September 30, 2016, and December 31, 2015, the Supplemental Executive Retirement Plan (SERP) rabbi trusts also included $16.7 million and $16.6 million , respectively, of fixed income funds valued at net asset value (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. (e) The fair value of the 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 September 30, 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 17 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. 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 July 1 $ (76.1 ) $ 0.8 Total realized/unrealized gains (losses): included in electric revenue 2.0 (0.2 ) included in purchased power expense 0.5 (0.2 ) included in non-operating income 3.8 3.2 included in interest charges (1.8 ) — included in regulatory (asset) liability 0.2 (0.1 ) Purchases — (0.2 ) Settlements (6.4 ) (2.9 ) Net asset (liability) at September 30 $ (77.8 ) $ 0.4 Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30: included in electric revenue $ — $ (0.1 ) included in interest charges (1.8 ) — included in regulatory (asset) liability 0.8 (0.1 ) 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 1.7 (7.9 ) included in purchased power expense 0.2 (1.4 ) included in non-operating income 7.9 6.9 included in interest charges (78.8 ) — included in regulatory (asset) liability 0.8 (0.1 ) Purchases (0.5 ) 0.4 Settlements (9.0 ) (1.0 ) Net asset (liability) at September 30 $ (77.8 ) $ 0.4 Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30: included in electric revenue $ — $ (0.1 ) included in non-operating income 0.1 (0.1 ) included in interest charges (78.8 ) — included in regulatory (asset) liability 0.8 (0.1 ) KCP&L Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative Instruments 2016 2015 (millions) Net asset at July 1 $ 0.5 $ 0.1 Total realized/unrealized gains (losses): included in electric revenue 2.0 (0.2 ) included in regulatory asset — (0.1 ) Purchases (0.1 ) (0.2 ) Settlements (2.0 ) 0.2 Net asset (liability) at September 30 $ 0.4 $ (0.2 ) Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30: included in electric revenue $ — $ (0.1 ) included in regulatory (asset) liability 0.5 (0.1 ) 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 1.7 (7.9 ) included in regulatory (asset) liability 0.5 (0.1 ) Purchases (0.5 ) (0.4 ) Settlements (0.9 ) 5.1 Net asset (liability) at September 30 $ 0.4 $ (0.2 ) Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30: included in electric revenue $ — $ (0.1 ) included in regulatory (asset) liability 0.5 (0.1 )

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss) [Text Block]	19 . 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) Year to Date September 30, 2016 Beginning balance January 1 $ (10.1 ) $ (1.9 ) $ (12.0 ) Amounts reclassified from accumulated other comprehensive loss 4.1 0.4 4.5 Net current period other comprehensive income 4.1 0.4 4.5 Ending balance September 30 $ (6.0 ) $ (1.5 ) $ (7.5 ) Year to Date September 30, 2015 Beginning balance January 1 $ (15.8 ) $ (2.9 ) $ (18.7 ) Amounts reclassified from accumulated other comprehensive loss 4.2 0.3 4.5 Net current period other comprehensive income 4.2 0.3 4.5 Ending balance September 30 $ (11.6 ) $ (2.6 ) $ (14.2 ) (a) Net of tax KCP&L Gains and Losses on Cash Flow Hedges (a) (millions) Year to date September 30, 2016 Beginning balance January 1 $ (9.6 ) Amounts reclassified from accumulated other comprehensive loss 4.0 Net current period other comprehensive income 4.0 Ending balance September 30 $ (5.6 ) Year to date September 30, 2015 Beginning balance January 1 $ (14.9 ) Amounts reclassified from accumulated other comprehensive loss 4.0 Net current period other comprehensive income 4.0 Ending balance September 30 $ (10.9 ) (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 Three Months Ended September 30 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (2.3 ) $ (2.3 ) Interest charges (2.3 ) (2.3 ) Income before income tax expense and income from equity investments 1.0 0.9 Income tax benefit $ (1.3 ) $ (1.4 ) Net income Amortization of defined benefit pension items Net losses included in net periodic benefit costs $ (0.2 ) $ (0.1 ) Utility operating and maintenance expenses (0.2 ) (0.1 ) Income before income tax expense and income from equity investments — 0.1 Income tax benefit $ (0.2 ) $ — Net income Total reclassifications, net of tax $ (1.5 ) $ (1.4 ) Net income Great Plains Energy Details about Accumulated Other Comprehensive Loss Components Amount Reclassified from Accumulated Other Comprehensive Loss Affected Line Item in the Income Statement Year to Date September 30 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (6.9 ) $ (6.9 ) Interest charges (6.9 ) (6.9 ) Income before income tax expense and income from equity investments 2.8 2.7 Income tax benefit $ (4.1 ) $ (4.2 ) Net income Amortization of defined benefit pension items Net losses included in net periodic benefit costs $ (0.6 ) $ (0.5 ) Utility operating and maintenance expenses (0.6 ) (0.5 ) Income before income tax expense and income from equity investments 0.2 0.2 Income tax benefit $ (0.4 ) $ (0.3 ) Net income Total reclassifications, net of tax $ (4.5 ) $ (4.5 ) 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 Three Months Ended September 30 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (2.2 ) $ (2.2 ) Interest charges (2.2 ) (2.2 ) Income before income tax expense 1.0 0.9 Income tax benefit Total reclassifications, net of tax $ (1.2 ) $ (1.3 ) 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 Year to Date September 30 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (6.6 ) $ (6.6 ) Interest charges (6.6 ) (6.6 ) Income before income tax expense 2.6 2.6 Income tax benefit Total reclassifications, net of tax $ (4.0 ) $ (4.0 ) Net income

Taxes

Taxes	9 Months Ended
	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	20. TAXES Components of income tax expense are detailed in the following tables. Three Months Ended September 30 Year to Date Great Plains Energy 2016 2015 2016 2015 Current income taxes (millions) Federal $ — $ (0.8 ) $ (0.1 ) $ (0.3 ) State — 0.5 0.3 0.4 Total — (0.3 ) 0.2 0.1 Deferred income taxes Federal 70.1 66.4 91.5 91.8 State 13.0 12.4 18.4 18.3 Total 83.1 78.8 109.9 110.1 Investment tax credit Deferral — 0.5 2.5 0.5 Amortization (0.4 ) (0.4 ) (1.1 ) (1.1 ) Total (0.4 ) 0.1 1.4 (0.6 ) Income tax expense $ 82.7 $ 78.6 $ 111.5 $ 109.6 Three Months Ended September 30 Year to Date KCP&L 2016 2015 2016 2015 Current income taxes (millions) Federal $ 35.4 $ 43.9 $ 36.6 $ 42.4 State 6.4 7.1 6.7 6.7 Total 41.8 51.0 43.3 49.1 Deferred income taxes Federal 22.5 (1.6 ) 61.5 14.6 State 4.5 0.8 12.5 5.2 Total 27.0 (0.8 ) 74.0 19.8 Investment tax credit Deferral — 0.5 — 0.5 Amortization (0.3 ) (0.2 ) (0.8 ) (0.7 ) Total (0.3 ) 0.3 (0.8 ) (0.2 ) Income tax expense $ 68.5 $ 50.5 $ 116.5 $ 68.7 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. Three Months Ended September 30 Year to Date Great Plains Energy 2016 2015 2016 2015 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.3 ) 0.3 (0.2 ) 0.4 Amortization of investment tax credits (0.2 ) (0.2 ) (0.4 ) (0.4 ) Federal income tax credits (1.1 ) (1.2 ) (2.7 ) (2.6 ) State income taxes 3.9 4.2 4.0 4.0 Transaction costs 1.0 — 1.0 — Other (0.1 ) 0.2 — 0.2 Effective income tax rate 38.2 % 38.3 % 36.7 % 36.6 % Three Months Ended September 30 Year to Date KCP&L 2016 2015 2016 2015 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.5 ) 0.4 (0.3 ) 0.6 Amortization of investment tax credits (0.1 ) (0.2 ) (0.2 ) (0.4 ) Federal income tax credits (1.2 ) (1.8 ) (2.3 ) (3.9 ) State income taxes 3.8 3.9 3.8 3.9 Other (0.2 ) 0.1 (0.1 ) (0.1 ) Effective income tax rate 36.8 % 37.4 % 35.9 % 35.1 %

Segments and Related Informatio

Segments and Related Information	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
Segments and Related Information	21 . 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 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. Three Months Ended September 30, 2016 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 856.8 $ — $ — $ 856.8 Depreciation and amortization (86.4 ) — — (86.4 ) Interest (charges) income (49.3 ) (26.4 ) 8.1 (67.6 ) Income tax (expense) benefit (95.9 ) 13.2 — (82.7 ) Net income (loss) 161.1 (27.5 ) — 133.6 Year to Date September 30, 2016 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 2,099.7 $ — $ — $ 2,099.7 Depreciation and amortization (256.9 ) — — (256.9 ) Interest (charges) income (147.4 ) (128.4 ) 24.1 (251.7 ) Income tax (expense) benefit (160.2 ) 48.7 — (111.5 ) Net income (loss) 278.4 (86.4 ) — 192.0 Three Months Ended September 30, 2015 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 781.4 $ — $ — $ 781.4 Depreciation and amortization (82.4 ) — — (82.4 ) Interest (charges) income (48.9 ) (10.2 ) 8.1 (51.0 ) Income tax expense (78.5 ) (0.1 ) — (78.6 ) Net income (loss) 129.1 (2.3 ) — 126.8 Year to Date September 30, 2015 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 1,939.5 $ — $ — $ 1,939.5 Depreciation and amortization (245.7 ) — — (245.7 ) Interest (charges) income (142.1 ) (30.3 ) 24.1 (148.3 ) Income tax (expense) benefit (112.0 ) 2.4 — (109.6 ) Net income (loss) 196.4 (6.3 ) — 190.1 Electric Utility Other Eliminations Great Plains Energy September 30, 2016 (millions) Assets $ 11,337.1 $ 114.5 $ (406.9 ) $ 11,044.7 Capital expenditures (a) 435.3 — — 435.3 December 31, 2015 Assets $ 11,045.5 $ (51.1 ) $ (255.8 ) $ 10,738.6 Capital expenditures (a) 677.1 — — 677.1 (a) Capital expenditures reflect year to date amounts for the periods presented.

Summary of Significant Accoun29

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 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. 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 21 for additional information.
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. The effect of dilutive securities, calculated using the treasury stock method, assumes the issuance of common shares applicable to performance shares and restricted stock.
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 Generally Accepted Accounting Principles (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 are evaluating the effect that ASU No. 2014-09 will have on their consolidated financial statements and related disclosures and have not yet selected a transition method nor have they determined the effect of the standard on their ongoing financial reporting. 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 plan to adopt ASU No. 2016-09 effective January 1, 2017 and it is not expected to have a significant impact on their ongoing financial reporting.

Summary of Significant Accoun30

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table reconciles Great Plains Energy's basic and diluted EPS. Three Months Ended September 30 Year to Date 2016 2015 2016 2015 Income (millions, except per share amounts) Net income $ 133.6 $ 126.8 $ 192.0 $ 190.1 Less: preferred stock dividend requirements and redemption premium 0.9 0.4 1.7 1.2 Earnings available for common shareholders $ 132.7 $ 126.4 $ 190.3 $ 188.9 Common Shares Outstanding Average number of common shares outstanding 154.6 154.2 154.5 154.1 Add: effect of dilutive securities 0.3 0.6 0.4 0.7 Diluted average number of common shares outstanding 154.9 154.8 154.9 154.8 Basic EPS $ 0.86 $ 0.82 $ 1.23 $ 1.23 Diluted EPS $ 0.86 $ 0.82 $ 1.23 $ 1.22

Supplemental Cash Flow Inform31

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2016
Supplemental Cash Flow Elements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	Great Plains Energy Other Operating Activities Year to Date September 30 2016 2015 Cash flows affected by changes in: (millions) Receivables $ (45.9 ) $ (13.2 ) Accounts receivable pledged as collateral (15.0 ) (19.0 ) Fuel inventories 19.8 (10.8 ) Materials and supplies (5.3 ) (2.9 ) Accounts payable (119.8 ) (121.9 ) Accrued taxes 97.2 89.2 Accrued interest 16.7 16.9 Deferred refueling outage costs 7.5 (12.8 ) Pension and post-retirement benefit obligations 53.2 48.8 Allowance for equity funds used during construction (4.3 ) (3.8 ) Fuel recovery mechanisms (16.8 ) 36.6 Other (11.7 ) 2.6 Total other operating activities $ (24.4 ) $ 9.7 Cash paid during the period: Interest $ 130.2 $ 121.2 Income taxes $ 0.2 $ 0.2 Non-cash investing activities: Liabilities accrued for capital expenditures $ 30.7 $ 23.4 KCP&L Other Operating Activities Year to Date September 30 2016 2015 Cash flows affected by changes in: (millions) Receivables $ (53.5 ) $ (6.2 ) Fuel inventories 12.7 (11.6 ) Materials and supplies (3.8 ) (4.0 ) Accounts payable (80.3 ) (83.1 ) Accrued taxes 179.3 162.3 Accrued interest 8.9 12.3 Deferred refueling outage costs 7.5 (12.8 ) Pension and post-retirement benefit obligations 53.7 48.8 Allowance for equity funds used during construction (4.0 ) (2.9 ) Fuel recovery mechanisms (31.0 ) 1.8 Other (14.8 ) (1.0 ) Total other operating activities $ 74.7 $ 103.6 Cash paid during the period: Interest $ 86.7 $ 79.1 Non-cash investing activities: Liabilities accrued for capital expenditures $ 25.7 $ 15.7

Receivables (Tables)

Receivables (Tables)	9 Months Ended
	Sep. 30, 2016
Receivables [Abstract]
Schedule of receivables [Table Text Block]	Great Plains Energy's and KCP&L's receivables are detailed in the following table. September 30 December 31 2016 2015 Great Plains Energy (millions) Customer accounts receivable - billed $ 55.3 $ 3.4 Customer accounts receivable - unbilled 89.3 71.6 Allowance for doubtful accounts - customer accounts receivable (5.1 ) (3.8 ) Other receivables 54.6 76.5 Total $ 194.1 $ 147.7 KCP&L Customer accounts receivable - billed $ 54.9 $ 2.8 Customer accounts receivable - unbilled 70.8 58.8 Allowance for doubtful accounts - customer accounts receivable (2.7 ) (1.8 ) Other receivables 45.7 69.4 Total $ 168.7 $ 129.2

Nuclear Plant (Tables)

Nuclear Plant (Tables)	9 Months Ended
	Sep. 30, 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. September 30 December 31 Decommissioning Trust (millions) Beginning balance January 1 $ 200.7 $ 199.0 Contributions 2.5 3.3 Earned income, net of fees 3.0 3.4 Net realized gains 0.2 0.7 Net unrealized gains (losses) 11.9 (5.7 ) Ending balance $ 218.3 $ 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. September 30, 2016 December 31, 2015 Cost Basis Unrealized Gains Unrealized Losses Fair Value Cost Basis Unrealized Gains Unrealized Losses Fair Value (millions) Equity securities $ 92.4 $ 56.2 $ (1.2 ) $ 147.4 $ 89.6 $ 47.9 $ (2.1 ) $ 135.4 Debt securities 64.5 4.8 — 69.3 59.6 2.6 (0.5 ) 61.7 Other 1.6 — — 1.6 3.6 — — 3.6 Total $ 158.5 $ 61.0 $ (1.2 ) $ 218.3 $ 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. Three Months Ended Year to Date 2016 2015 2016 2015 (millions) Realized gains $ 0.6 $ 0.6 $ 1.5 $ 3.2 Realized losses (0.3 ) (0.5 ) (1.3 ) (2.3 )

Pension Plans and Other Emplo34

Pension Plans and Other Employee Benefits (Tables)	9 Months Ended
	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Schedule of Net Benefit Costs [Table Text Block]	The following tables provide Great Plains Energy's components of net periodic benefit costs prior to the effects of capitalization and sharing with joint owners of power plants. Pension Benefits Other Benefits Three Months Ended September 30 2016 2015 2016 2015 Components of net periodic benefit costs (millions) Service cost $ 10.5 $ 11.4 $ 0.7 $ 0.8 Interest cost 13.2 12.5 1.5 1.7 Expected return on plan assets (12.3 ) (13.0 ) (0.8 ) (0.7 ) Prior service cost 0.2 0.2 0.3 0.7 Recognized net actuarial (gain)/loss 13.0 12.9 (0.3 ) 0.1 Transition obligation — — — 0.1 Net periodic benefit costs before regulatory adjustment 24.6 24.0 1.4 2.7 Regulatory adjustment (1.1 ) (3.5 ) 1.4 1.4 Net periodic benefit costs $ 23.5 $ 20.5 $ 2.8 $ 4.1 Pension Benefits Other Benefits Year to Date September 30 2016 2015 2016 2015 Components of net periodic benefit costs (millions) Service cost $ 31.5 $ 34.0 $ 2.0 $ 2.5 Interest cost 39.7 37.7 4.6 5.1 Expected return on plan assets (36.9 ) (38.8 ) (2.3 ) (2.2 ) Prior service cost 0.5 0.6 0.9 2.3 Recognized net actuarial (gain)/loss 38.9 38.5 (1.1 ) 0.2 Transition obligation — — — 0.1 Net periodic benefit costs before regulatory adjustment 73.7 72.0 4.1 8.0 Regulatory adjustment (3.1 ) (9.3 ) 4.4 4.2 Net periodic benefit costs $ 70.6 $ 62.7 $ 8.5 $ 12.2

Equity Compensation (Tables)

Equity Compensation (Tables)	9 Months Ended
	Sep. 30, 2016
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Equity compensation expense and associated income tax benefits	Three Months Ended September 30 Year to Date September 30 2016 2015 2016 2015 Great Plains Energy (millions) Equity compensation expense $ 0.4 $ 3.7 $ 3.9 $ 4.6 Income tax benefit — 1.4 1.3 1.7 KCP&L Equity compensation expense $ 0.2 $ 2.5 $ 2.5 $ 3.1 Income tax benefit — 0.9 0.8 1.1
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 September 30, 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 (73,417 ) 22.69 Forfeited (572 ) 27.51 Ending balance September 30, 2016 253,572 27.13

Long-Term Debt (Tables)

Long-Term Debt (Tables)	9 Months Ended
	Sep. 30, 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. September 30 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 0.76% 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 (15.9 ) (17.3 ) Total KCP&L excluding current maturities (d) 2,283.5 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 (1.9 ) (2.1 ) Total Great Plains Energy excluding current maturities (d) $ 3,364.6 $ 3,745.1 (a) Weighted-average interest rates at September 30, 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 September 30, 2016, and December 31, 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

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Schedule Of Environmental Capital Expenditures [Table Text Block]	2016 2017 2018 2019 2020 (millions) Great Plains Energy $ 99.6 $ 45.5 $ 20.6 $ 98.9 $ 151.9 KCP&L 83.8 30.1 14.4 87.3 130.0

Related Party Transactions an38

Related Party Transactions and Relationships (Tables)	9 Months Ended
	Sep. 30, 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. September 30 December 31 2016 2015 (millions) Net receivable from GMO $ 71.5 $ 50.0 Net receivable from Great Plains Energy 19.5 15.8

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 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. September 30 December 31 2016 2015 Notional Contract Amount Fair Value Notional Contract Amount Fair Value Great Plains Energy (millions) Non-hedging derivatives Futures contracts $ 14.9 $ — $ 26.6 $ (5.7 ) Forward contracts 11.1 2.6 15.6 3.1 Transmission congestion rights 5.1 0.7 5.6 (0.5 ) Interest rate swaps 4,415.0 (78.8 ) — — KCP&L Non-hedging derivatives Futures contracts $ 0.2 $ — $ 0.9 $ (0.1 ) Transmission congestion rights 3.9 0.4 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 September 30, 2016 Classification Fair Value Fair Value Derivatives Not Designated as Hedging Instruments (millions) Commodity contracts Other $ 5.3 $ 2.0 Interest rate contracts Derivative instruments — 78.8 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 September 30, 2016 Classification Fair Value Fair Value Derivatives Not Designated as Hedging Instruments (millions) Commodity contracts Other $ 1.1 $ 0.7 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 September 30, 2016 (millions) Derivative assets $ 5.3 $ (2.0 ) $ 3.3 $ — $ — $ 3.3 Derivative liabilities 80.8 (2.0 ) 78.8 — — 78.8 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 September 30, 2016 (millions) Derivative assets $ 1.1 $ (0.7 ) $ 0.4 $ — $ — $ 0.4 Derivative liabilities 0.7 (0.7 ) — — — — 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 Three Months Ended September 30 Year to Date Derivatives Not Designated as Hedging Instruments 2016 2015 2016 2015 Location of Gain (Loss) (millions) Electric revenues $ 2.0 $ (0.2 ) $ 1.7 $ (7.9 ) Fuel (0.1 ) (0.1 ) (4.6 ) (1.2 ) Purchased power 0.5 (0.2 ) 0.2 (1.4 ) Interest charges (1.8 ) — (78.8 ) — Regulatory asset — (1.9 ) (0.1 ) (5.1 ) Regulatory liability (0.3 ) — 0.9 — Total $ 0.3 $ (2.4 ) $ (80.7 ) $ (15.6 ) KCP&L Three Months Ended September 30 Year to Date Derivatives Not Designated as Hedging Instruments 2016 2015 2016 2015 Location of Gain (Loss) (millions) Electric revenues $ 2.0 $ (0.2 ) $ 1.7 $ (7.9 ) Fuel 0.3 1.1 0.2 1.3 Regulatory asset 0.1 (0.1 ) — (0.1 ) Regulatory liability — — 0.5 — Total $ 2.4 $ 0.8 $ 2.4 $ (6.7 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 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 September 30 Level 1 Level 2 Level 3 KCP&L (millions) Assets Nuclear decommissioning trust (a) Equity securities $ 147.4 $ 147.4 $ — $ — Debt securities U.S. Treasury 29.7 29.7 — — U.S. Agency 1.8 — 1.8 — State and local obligations 3.1 — 3.1 — Corporate bonds 34.4 — 34.4 — Foreign governments 0.3 — 0.3 — Cash equivalents 1.6 1.6 — — Total nuclear decommissioning trust 218.3 178.7 39.6 — Self-insured health plan trust (b) Equity securities 0.9 0.9 — — Debt securities 4.8 — 4.8 — Cash and cash equivalents 8.0 8.0 — — Total self-insured health plan trust 13.7 8.9 4.8 — Derivative instruments - commodity (c) 1.1 — — 1.1 Total $ 233.1 $ 187.6 $ 44.4 $ 1.1 Liabilities Derivative instruments - commodity (c) 0.7 — — 0.7 Total $ 0.7 $ — $ — $ 0.7 Other Great Plains Energy Assets Derivative instruments - commodity (c) $ 4.2 $ 1.1 $ 2.3 $ 0.8 SERP rabbi trusts (d) Equity securities 0.1 0.1 — — Total $ 4.3 $ 1.2 $ 2.3 $ 0.8 Liabilities Derivative instruments Commodity (c) $ 1.3 $ 1.1 $ — $ 0.2 Interest rates (e) 78.8 — — 78.8 Total derivative instruments 80.1 1.1 — 79.0 Total $ 80.1 $ 1.1 $ — $ 79.0 Great Plains Energy Assets Nuclear decommissioning trust (a) $ 218.3 $ 178.7 $ 39.6 $ — Self-insured health plan trust (b) 13.7 8.9 4.8 — Derivative instruments (c) 5.3 1.1 2.3 1.9 SERP rabbi trusts (d) 0.1 0.1 — — Total $ 237.4 $ 188.8 $ 46.7 $ 1.9 Liabilities Derivative instruments (c) (e) 80.8 1.1 — 79.7 Total $ 80.8 $ 1.1 $ — $ 79.7 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 (d) 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 (d) 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 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) At September 30, 2016, and December 31, 2015, the Supplemental Executive Retirement Plan (SERP) rabbi trusts also included $16.7 million and $16.6 million , respectively, of fixed income funds valued at net asset value (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. (e) The fair value of the 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 September 30, 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 17 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.
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 July 1 $ (76.1 ) $ 0.8 Total realized/unrealized gains (losses): included in electric revenue 2.0 (0.2 ) included in purchased power expense 0.5 (0.2 ) included in non-operating income 3.8 3.2 included in interest charges (1.8 ) — included in regulatory (asset) liability 0.2 (0.1 ) Purchases — (0.2 ) Settlements (6.4 ) (2.9 ) Net asset (liability) at September 30 $ (77.8 ) $ 0.4 Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30: included in electric revenue $ — $ (0.1 ) included in interest charges (1.8 ) — included in regulatory (asset) liability 0.8 (0.1 ) 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 1.7 (7.9 ) included in purchased power expense 0.2 (1.4 ) included in non-operating income 7.9 6.9 included in interest charges (78.8 ) — included in regulatory (asset) liability 0.8 (0.1 ) Purchases (0.5 ) 0.4 Settlements (9.0 ) (1.0 ) Net asset (liability) at September 30 $ (77.8 ) $ 0.4 Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30: included in electric revenue $ — $ (0.1 ) included in non-operating income 0.1 (0.1 ) included in interest charges (78.8 ) — included in regulatory (asset) liability 0.8 (0.1 ) KCP&L Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative Instruments 2016 2015 (millions) Net asset at July 1 $ 0.5 $ 0.1 Total realized/unrealized gains (losses): included in electric revenue 2.0 (0.2 ) included in regulatory asset — (0.1 ) Purchases (0.1 ) (0.2 ) Settlements (2.0 ) 0.2 Net asset (liability) at September 30 $ 0.4 $ (0.2 ) Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30: included in electric revenue $ — $ (0.1 ) included in regulatory (asset) liability 0.5 (0.1 ) 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 1.7 (7.9 ) included in regulatory (asset) liability 0.5 (0.1 ) Purchases (0.5 ) (0.4 ) Settlements (0.9 ) 5.1 Net asset (liability) at September 30 $ 0.4 $ (0.2 ) Total unrealized gains (losses) relating to assets and liabilities still on the consolidated balance sheet at September 30: included in electric revenue $ — $ (0.1 ) included in regulatory (asset) liability 0.5 (0.1 )

Accumulated Other Comprehensi41

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 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) Year to Date September 30, 2016 Beginning balance January 1 $ (10.1 ) $ (1.9 ) $ (12.0 ) Amounts reclassified from accumulated other comprehensive loss 4.1 0.4 4.5 Net current period other comprehensive income 4.1 0.4 4.5 Ending balance September 30 $ (6.0 ) $ (1.5 ) $ (7.5 ) Year to Date September 30, 2015 Beginning balance January 1 $ (15.8 ) $ (2.9 ) $ (18.7 ) Amounts reclassified from accumulated other comprehensive loss 4.2 0.3 4.5 Net current period other comprehensive income 4.2 0.3 4.5 Ending balance September 30 $ (11.6 ) $ (2.6 ) $ (14.2 ) (a) Net of tax KCP&L Gains and Losses on Cash Flow Hedges (a) (millions) Year to date September 30, 2016 Beginning balance January 1 $ (9.6 ) Amounts reclassified from accumulated other comprehensive loss 4.0 Net current period other comprehensive income 4.0 Ending balance September 30 $ (5.6 ) Year to date September 30, 2015 Beginning balance January 1 $ (14.9 ) Amounts reclassified from accumulated other comprehensive loss 4.0 Net current period other comprehensive income 4.0 Ending balance September 30 $ (10.9 ) (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 Three Months Ended September 30 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (2.3 ) $ (2.3 ) Interest charges (2.3 ) (2.3 ) Income before income tax expense and income from equity investments 1.0 0.9 Income tax benefit $ (1.3 ) $ (1.4 ) Net income Amortization of defined benefit pension items Net losses included in net periodic benefit costs $ (0.2 ) $ (0.1 ) Utility operating and maintenance expenses (0.2 ) (0.1 ) Income before income tax expense and income from equity investments — 0.1 Income tax benefit $ (0.2 ) $ — Net income Total reclassifications, net of tax $ (1.5 ) $ (1.4 ) Net income Great Plains Energy Details about Accumulated Other Comprehensive Loss Components Amount Reclassified from Accumulated Other Comprehensive Loss Affected Line Item in the Income Statement Year to Date September 30 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (6.9 ) $ (6.9 ) Interest charges (6.9 ) (6.9 ) Income before income tax expense and income from equity investments 2.8 2.7 Income tax benefit $ (4.1 ) $ (4.2 ) Net income Amortization of defined benefit pension items Net losses included in net periodic benefit costs $ (0.6 ) $ (0.5 ) Utility operating and maintenance expenses (0.6 ) (0.5 ) Income before income tax expense and income from equity investments 0.2 0.2 Income tax benefit $ (0.4 ) $ (0.3 ) Net income Total reclassifications, net of tax $ (4.5 ) $ (4.5 ) 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 Three Months Ended September 30 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (2.2 ) $ (2.2 ) Interest charges (2.2 ) (2.2 ) Income before income tax expense 1.0 0.9 Income tax benefit Total reclassifications, net of tax $ (1.2 ) $ (1.3 ) 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 Year to Date September 30 2016 2015 (millions) Gains and (losses) on cash flow hedges (effective portion) Interest rate contracts $ (6.6 ) $ (6.6 ) Interest charges (6.6 ) (6.6 ) Income before income tax expense 2.6 2.6 Income tax benefit Total reclassifications, net of tax $ (4.0 ) $ (4.0 ) Net income

Taxes (Tables)

Taxes (Tables)	9 Months Ended
	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Components of income tax expense are detailed in the following tables. Three Months Ended September 30 Year to Date Great Plains Energy 2016 2015 2016 2015 Current income taxes (millions) Federal $ — $ (0.8 ) $ (0.1 ) $ (0.3 ) State — 0.5 0.3 0.4 Total — (0.3 ) 0.2 0.1 Deferred income taxes Federal 70.1 66.4 91.5 91.8 State 13.0 12.4 18.4 18.3 Total 83.1 78.8 109.9 110.1 Investment tax credit Deferral — 0.5 2.5 0.5 Amortization (0.4 ) (0.4 ) (1.1 ) (1.1 ) Total (0.4 ) 0.1 1.4 (0.6 ) Income tax expense $ 82.7 $ 78.6 $ 111.5 $ 109.6 Three Months Ended September 30 Year to Date KCP&L 2016 2015 2016 2015 Current income taxes (millions) Federal $ 35.4 $ 43.9 $ 36.6 $ 42.4 State 6.4 7.1 6.7 6.7 Total 41.8 51.0 43.3 49.1 Deferred income taxes Federal 22.5 (1.6 ) 61.5 14.6 State 4.5 0.8 12.5 5.2 Total 27.0 (0.8 ) 74.0 19.8 Investment tax credit Deferral — 0.5 — 0.5 Amortization (0.3 ) (0.2 ) (0.8 ) (0.7 ) Total (0.3 ) 0.3 (0.8 ) (0.2 ) Income tax expense $ 68.5 $ 50.5 $ 116.5 $ 68.7
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	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. Three Months Ended September 30 Year to Date Great Plains Energy 2016 2015 2016 2015 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.3 ) 0.3 (0.2 ) 0.4 Amortization of investment tax credits (0.2 ) (0.2 ) (0.4 ) (0.4 ) Federal income tax credits (1.1 ) (1.2 ) (2.7 ) (2.6 ) State income taxes 3.9 4.2 4.0 4.0 Transaction costs 1.0 — 1.0 — Other (0.1 ) 0.2 — 0.2 Effective income tax rate 38.2 % 38.3 % 36.7 % 36.6 % Three Months Ended September 30 Year to Date KCP&L 2016 2015 2016 2015 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % 35.0 % Differences between book and tax depreciation not normalized (0.5 ) 0.4 (0.3 ) 0.6 Amortization of investment tax credits (0.1 ) (0.2 ) (0.2 ) (0.4 ) Federal income tax credits (1.2 ) (1.8 ) (2.3 ) (3.9 ) State income taxes 3.8 3.9 3.8 3.9 Other (0.2 ) 0.1 (0.1 ) (0.1 ) Effective income tax rate 36.8 % 37.4 % 35.9 % 35.1 %

Segments and Related Informat43

Segments and Related Information (Tables)	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
Segment Financial Information [Table Text Block]	The following tables reflect summarized financial information concerning Great Plains Energy's reportable segment. Three Months Ended September 30, 2016 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 856.8 $ — $ — $ 856.8 Depreciation and amortization (86.4 ) — — (86.4 ) Interest (charges) income (49.3 ) (26.4 ) 8.1 (67.6 ) Income tax (expense) benefit (95.9 ) 13.2 — (82.7 ) Net income (loss) 161.1 (27.5 ) — 133.6 Year to Date September 30, 2016 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 2,099.7 $ — $ — $ 2,099.7 Depreciation and amortization (256.9 ) — — (256.9 ) Interest (charges) income (147.4 ) (128.4 ) 24.1 (251.7 ) Income tax (expense) benefit (160.2 ) 48.7 — (111.5 ) Net income (loss) 278.4 (86.4 ) — 192.0 Three Months Ended September 30, 2015 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 781.4 $ — $ — $ 781.4 Depreciation and amortization (82.4 ) — — (82.4 ) Interest (charges) income (48.9 ) (10.2 ) 8.1 (51.0 ) Income tax expense (78.5 ) (0.1 ) — (78.6 ) Net income (loss) 129.1 (2.3 ) — 126.8 Year to Date September 30, 2015 Electric Utility Other Eliminations Great Plains Energy (millions) Operating revenues $ 1,939.5 $ — $ — $ 1,939.5 Depreciation and amortization (245.7 ) — — (245.7 ) Interest (charges) income (142.1 ) (30.3 ) 24.1 (148.3 ) Income tax (expense) benefit (112.0 ) 2.4 — (109.6 ) Net income (loss) 196.4 (6.3 ) — 190.1 Electric Utility Other Eliminations Great Plains Energy September 30, 2016 (millions) Assets $ 11,337.1 $ 114.5 $ (406.9 ) $ 11,044.7 Capital expenditures (a) 435.3 — — 435.3 December 31, 2015 Assets $ 11,045.5 $ (51.1 ) $ (255.8 ) $ 10,738.6 Capital expenditures (a) 677.1 — — 677.1

Summary of Significant Accoun44

Summary of Significant Accounting Policies Equity Method Investment (Details) - Transource Energy, LLC [Member]	9 Months Ended
	Sep. 30, 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 Accoun45

Summary of Significant Accounting Policies Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income [Abstract]
Net income	$ 133.6	$ 126.8	$ 192	$ 190.1
Less: preferred stock dividend requirements and redemption premium	0.9	0.4	1.7	1.2
Earnings available for common shareholders	$ 132.7	$ 126.4	$ 190.3	$ 188.9
Common Shares Outstanding [Abstract]
Average number of common shares outstanding (in shares)	154.6	154.2	154.5	154.1
Add: effect of dilutive securities (in shares)	0.3	0.6	0.4	0.7
Diluted average number of common shares outstanding (in shares)	154.9	154.8	154.9	154.8
Earnings Per Share [Abstract]
Basic EPS	$ 0.86	$ 0.82	$ 1.23	$ 1.23
Diluted EPS	$ 0.86	$ 0.82	$ 1.23	$ 1.22

Summary of Significant Accoun46

Summary of Significant Accounting Policies Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0	0	0	0

Summary of Significant Accoun47

Summary of Significant Accounting Policies Subsequent Events (Details) - Subsequent Event [Member] - $ / shares	1 Months Ended
	Nov. 30, 2016	Oct. 31, 2016
Kansas City Power and Light Company [Member]
Dividends Declared [Abstract]
Dividends Payable, Date Declared, Month and Year	2016-11
Dividends Payable, Amount Per Share	$ 45,000,000
Dividends Payable, Date to be Paid	Dec. 19, 2016
Common Stock [Member]
Dividends Declared [Abstract]
Dividends Payable, Date Declared, Month and Year	2016-11
Dividends Payable, Amount Per Share	$ 0.2750
Dividends Payable, Date to be Paid	Dec. 20, 2016
Dividends Payable, Date of Record	Nov. 29, 2016
7.00% Mandatory Convertible Preferred Stock, Series B
Dividends Declared [Abstract]
Dividends Payable, Date to be Paid	Dec. 15, 2016
Dividends Payable, Date of Record	Dec. 1, 2016
Preferred Stock, Dividend Rate, Percentage	7.00%	7.00%

Anticipated Acquisition of We48

Anticipated Acquisition of Westar Energy, Inc. (Details) $ / shares in Units, $ in Millions	Oct. 03, 2016USD ($)$ / sharesshares	May 29, 2016USD ($)$ / sharesRateshares	Oct. 31, 2016USD ($)$ / sharesshares	Sep. 30, 2016USD ($)shares	Sep. 30, 2015USD ($)shares	Nov. 03, 2016USD ($)
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
Net Proceeds from Issuance of Common Stock				$ 2.4	$ 2.3
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]
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
Bridge Loan [Member] | Great Plains Energy [Member] | Subsequent Event [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
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
Preferred Stock, Dividend Rate, Percentage | Rate		7.25%
Preferred Stock, Purchase Agreement, Proceeds		$ 750
Depositary Shares [Member] | Subsequent Event [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
Gross Proceeds from Issuance of Depositary Shares	$ 862.5		$ 862.5
Net Proceeds from Issuance of Depositary Shares	$ 836.6		$ 836.6
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				420,207	210,579
Common Stock [Member] | Subsequent Event [Member]
Anticipated Acquisition Of Westar Energy, Inc. [Line Items]
Stock Issued During Period, Shares, New Issues | shares	60,500,000		60,500,000
Shares Issued, Price Per Share | $ / shares	$ 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

Supplemental Cash Flow Inform49

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows affected by changes in:
Receivables	$ (45.9)	$ (13.2)
Accounts receivable pledged as collateral	(15)	(19)
Fuel inventories	19.8	(10.8)
Materials and supplies	(5.3)	(2.9)
Accounts payable	(119.8)	(121.9)
Accrued taxes	97.2	89.2
Accrued interest	16.7	16.9
Deferred refueling outage costs	7.5	(12.8)
Pension and post-retirement benefit obligations	53.2	48.8
Allowance for equity funds used during construction	(4.3)	(3.8)
Fuel recovery mechanisms	(16.8)	36.6
Other	(11.7)	2.6
Total other operating activities	(24.4)	9.7
Cash paid during the period:
Interest	130.2	121.2
Income taxes	0.2	0.2
Non-cash investing activities:
Liabilities accrued for capital expenditures	30.7	23.4
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	(53.5)	(6.2)
Fuel inventories	12.7	(11.6)
Materials and supplies	(3.8)	(4)
Accounts payable	(80.3)	(83.1)
Accrued taxes	179.3	162.3
Accrued interest	8.9	12.3
Deferred refueling outage costs	7.5	(12.8)
Pension and post-retirement benefit obligations	53.7	48.8
Allowance for equity funds used during construction	(4)	(2.9)
Fuel recovery mechanisms	(31)	1.8
Other	(14.8)	(1)
Total other operating activities	74.7	103.6
Cash paid during the period:
Interest	86.7	79.1
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 25.7	$ 15.7

Receivables Accounts, Notes, an

Receivables Accounts, Notes, and Financing (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	$ 54.6	$ 76.5
Total	194.1	147.7
Kansas City Power and Light Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other receivables	45.7	69.4
Total	168.7	129.2
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for doubtful accounts	(5.1)	(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	(2.7)	(1.8)
Trade Accounts Receivable [Member] | Billed Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	55.3	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	54.9	2.8
Trade Accounts Receivable [Member] | Unbilled Revenues [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts Receivable, Gross, Current	89.3	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	$ 70.8	$ 58.8

Receivables Narrative (Details)

Receivables Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Sale Of Accounts Receivable - KCPL and GMO
Accounts receivable pledged as collateral	$ 190	$ 175
Collateralized note payable	190	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	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Investments in decommissioning trust fund [Line Items]
Cost Basis	$ 158.5		$ 158.5		$ 152.8
Unrealized Gains	61		61		50.5
Unrealized Losses	(1.2)		(1.2)		(2.6)
Fair Value	218.3		$ 218.3		200.7	$ 199
Weighted average maturity of debt securities (in years)			8 years
Realized gains	0.6	$ 0.6	$ 1.5	$ 3.2
Realized losses	(0.3)	$ (0.5)	(1.3)	$ (2.3)
Equity Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	92.4		92.4		89.6
Unrealized Gains	56.2		56.2		47.9
Unrealized Losses	(1.2)		(1.2)		(2.1)
Fair Value	147.4		147.4		135.4
Debt Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	64.5		64.5		59.6
Unrealized Gains	4.8		4.8		2.6
Unrealized Losses	0		0		(0.5)
Fair Value	69.3		69.3		61.7
Other Securities [Member]
Investments in decommissioning trust fund [Line Items]
Cost Basis	1.6		1.6		3.6
Fair Value	$ 1.6		$ 1.6		$ 3.6

Nuclear Plant Decommissioning T

Nuclear Plant Decommissioning Trust (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2016
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	$ 200.7	$ 199
Contributions	2.5	3.3
Earned income, net of fees	3	3.4
Net realized gains	0.2	0.7
Net unrealized gains (losses)	11.9	(5.7)
Ending balance	218.3	200.7
Kansas City Power and Light Company [Member]
Nuclear decommissioning trust fund [Roll Forward]
Beginning balance January 1	200.7	199
Contributions	2.5	3.3
Earned income, net of fees	3	3.4
Net realized gains	0.2	0.7
Net unrealized gains (losses)	11.9	(5.7)
Ending balance	$ 218.3	$ 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%		47.00%

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Millions	1 Months Ended
	Sep. 30, 2016	Jul. 31, 2016	Feb. 29, 2016	Sep. 30, 2015
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%
Annual revenue increase authorized				$ 89.7
Return on equity, approved (in hundredths)				9.50%
Ratemaking equity ratio, approved (in hundredths)				50.09%
Kansas City Power and Light Company [Member] | Kansas Corporation Commission [Member]
Regulatory Proceedings [Line Items]
Annual revenue increase authorized				$ 48.7
Return on equity, approved (in hundredths)				9.30%
Ratemaking equity ratio, approved (in hundredths)				50.48%
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] | KCPL Greater Missouri Operations [Member] | Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Return on equity, approved (in hundredths)	9.75%
Minimum [Member] | KCPL Greater Missouri Operations [Member] | Missouri Public Service Commission [Member]
Regulatory Proceedings [Line Items]
Return on equity, approved (in hundredths)	9.50%

Goodwill (Details)

Goodwill (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 169	$ 169

Pension Plans and Other Emplo56

Pension Plans and Other Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Contributions by Employer			$ 23.6
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year			52.4
Components of net periodic benefit costs [Abstract]
Service cost	$ 10.5	$ 11.4	31.5	$ 34
Interest cost	13.2	12.5	39.7	37.7
Expected return on plan assets	(12.3)	(13)	(36.9)	(38.8)
Prior service cost	0.2	0.2	0.5	0.6
Recognized net actuarial (gain)/loss	13	12.9	38.9	38.5
Transition obligation	0	0	0	0
Net periodic benefit costs before regulatory adjustment	24.6	24	73.7	72
Regulatory adjustment	(1.1)	(3.5)	(3.1)	(9.3)
Net periodic benefit costs	23.5	20.5	70.6	62.7
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year			5.1
Components of net periodic benefit costs [Abstract]
Service cost	0.7	0.8	2	2.5
Interest cost	1.5	1.7	4.6	5.1
Expected return on plan assets	(0.8)	(0.7)	(2.3)	(2.2)
Prior service cost	0.3	0.7	0.9	2.3
Recognized net actuarial (gain)/loss	(0.3)	0.1	(1.1)	0.2
Transition obligation	0	0.1	0	0.1
Net periodic benefit costs before regulatory adjustment	1.4	2.7	4.1	8
Regulatory adjustment	1.4	1.4	4.4	4.2
Net periodic benefit costs	$ 2.8	$ 4.1	$ 8.5	$ 12.2
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%		47.00%		47.00%

Equity Compensation (Details)

Equity Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 0.4	$ 3.7	$ 3.9	$ 4.6
Income tax benefit	$ 0	$ 1.4	$ 1.3	$ 1.7
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility			18.00%
Expected dividend yield (in hundredths)			3.61%
Risk-free interest rate			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)	0		225,204
Earned (in shares)			(306,953)
Forfeited (in shares)			(1,714)
Performance adjustment (in shares)			99,553
Ending balance (in shares)	625,100		625,100
Weighted average beginning balance (in dollars per share)			$ 25.60
Weighted average granted (in dollars per share)		$ 22.46	31.41	$ 24.03
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		$ 28.13
Total unrecognized compensation expense	$ 7.7		$ 7.7
Remaining weighted-average contractual term (in years)			1 year 5 months
Fair value of performance shares earned and paid			$ 7.4	$ 0.5
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)			231,508
Granted (in shares)	0		96,053
Vested (in shares)			(73,417)
Forfeited (in shares)			(572)
Ending balance (in shares)	253,572		253,572
Weighted average beginning balance (in dollars per share)			$ 24.78
Weighted average granted (in dollars per share)		$ 24.20	29.41	$ 25.88
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)	$ 27.13		$ 27.13
Total unrecognized compensation expense	$ 3.2		$ 3.2
Total fair value of shares vested	0.1	$ 0.1	$ 1.7	$ 2.1
Remaining weighted-average contractual term (in years)			1 year 4 months
Kansas City Power and Light Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	0.2	2.5	$ 2.5	3.1
Income tax benefit	$ 0	$ 0.9	$ 0.8	$ 1.1

Short-term Borrowings and Sho58

Short-term Borrowings and Short-term Bank Lines of Credit (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Nov. 03, 2016	May 29, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Amount of outstanding cash borrowings	$ 104			$ 10
Commercial paper outstanding	157.1			224
Great Plains Energy [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Amount of credit facility	$ 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	$ 104			$ 10
Weighted-average interest rate from outstanding borrowings	2.06%			1.94%
Amount of letters of credit outstanding	$ 0.2			$ 0.2
Great Plains Energy [Member] | Bridge Loan [Member]
Short-term Debt [Line Items]
Amount of credit facility	8,017		$ 8,017
Great Plains Energy [Member] | Bridge Loan [Member] | Subsequent Event [Member]
Short-term Debt [Line Items]
Amount of credit facility, as amended		$ 5,100
Kansas City Power and Light Company [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	0			$ 180.3
Weighted-average interest rate from outstanding borrowings				0.70%
Kansas City Power and Light Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Amount of credit facility	$ 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	$ 157.1			$ 43.7
Weighted-average interest rate from outstanding borrowings	0.71%			0.65%
KCPL Greater Missouri Operations [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Amount of credit facility	$ 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	$ 2.1			$ 2.5

Long-Term Debt (Details)

Long-Term Debt (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Current maturities	$ (382.1)	$ (1.1)
Long-term debt excluding current maturities	3,364.6	3,745.1
Kansas City Power and Light Company [Member]
Debt Instrument [Line Items]
Current maturities	(281)	0
Unamortized discount and premium, net and debt issuance costs	(15.9)	(17.3)
Long-term debt excluding current maturities	2,283.5	2,563.1
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%
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
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)	0.76%
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 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 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 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] | 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	$ (1.9)	$ (2.1)

Common Shareholders' Equity (De

Common Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	Oct. 03, 2016	Oct. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Common Shareholders' Equity [Line Items]
Common Stock, Shares Authorized			600,000,000		250,000,000
Common Stock Shares Authorized Prior to Amended Articles of Incorporation			250,000,000
Net Proceeds from Issuance of Common Stock			$ 2.4	$ 2.3
Common Stock [Member]
Common Shareholders' Equity [Line Items]
Stock Issued During Period, Shares, New Issues			420,207	210,579
Common Stock [Member] | Subsequent Event [Member]
Common Shareholders' Equity [Line Items]
Shares Issued, Price Per Share	$ 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
Stock Issued During Period, Shares, New Issues	60,500,000	60,500,000

Preferred Stock (Details)

Preferred Stock (Details) $ / shares in Units, $ in Millions	Oct. 03, 2016USD ($)$ / sharesshares	May 29, 2016USD ($)years$ / sharesRateshares	Nov. 30, 2016Rate	Oct. 31, 2016USD ($)$ / sharesRateshares	Aug. 31, 2016USD ($)$ / sharesRateshares	Sep. 30, 2016USD ($)$ / sharesRate	Sep. 30, 2015USD ($)	Dec. 31, 2015USD ($)$ / sharesRate
Class of Stock [Line Items]
Preferred Stock, Value, Issued | $						$ 0		$ 39
Cumulative Preferred Stock [Abstract]
Cumulative preferred stock redemption | $						40.1	$ 0
Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Par or Stated Value Per Share					$ 100
Cumulative Preferred Stock [Abstract]
Preferred Stock, Shares Redeemed | shares					390,000
Cumulative preferred stock redemption | $					$ 40.1
Preferred Stock 3 Point 80 [Member]
Class of Stock [Line Items]
Preferred Stock, Value, Issued | $						$ 0		$ 10
Preferred Stock, Par or Stated Value Per Share						$ 100		$ 100
Preferred Stock, Dividend Rate, Percentage | Rate					3.80%	3.80%		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, Value, Issued | $						$ 0		$ 7
Preferred Stock, Par or Stated Value Per Share						$ 100		$ 100
Preferred Stock, Dividend Rate, Percentage | Rate					4.20%	4.20%		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, Value, Issued | $						$ 0		$ 12
Preferred Stock, Par or Stated Value Per Share						$ 100		$ 100
Preferred Stock, Dividend Rate, Percentage | Rate					4.35%	4.35%		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, Value, Issued | $						$ 0		$ 10
Preferred Stock, Par or Stated Value Per Share						$ 100		$ 100
Preferred Stock, Dividend Rate, Percentage | Rate					4.50%	4.50%		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%
Mandatory Convertible Preferred Stock [Abstract]
Preferred Shares To Be Issued, Stock Purchase Agreement, Series A Preferred Stock | shares		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 | Subsequent Event [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage | Rate			7.00%	7.00%
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
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] | Subsequent Event [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
Gross Proceeds from Issuance of Depositary Shares | $	$ 862.5			$ 862.5
Net Proceeds from Issuance of Depositary Shares | $	$ 836.6			$ 836.6
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 | Subsequent Event [Member]
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 | Subsequent Event [Member]
Mandatory Convertible Preferred Stock [Abstract]
Applicable Market Value Less Than Maximum Greater Than Minimum				$ 31.74

Commitments and Contingencies E

Commitments and Contingencies Environmental Matters (Details) T in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2016USD ($)TMW	Dec. 31, 2015USD ($)
Estimated Environmental Capital Expenditures [Abstract]
Estimate Of Environmental Capital Expenditures Current	$ 99.6
Estimate Of Environmental Capital Expenditures In Two Years	45.5
Estimate Of Environmental Capital Expenditures In Three Years	20.6
Estimate Of Environmental Capital Expenditures In Four Years	98.9
Estimate Of Environmental Capital Expenditures In Five Years	$ 151.9
Mercury and Air Toxics Standards Rule [Abstract]
Capacity of electric steam generating units that fall under MACT standards (in megawatts) | MW	25
Climate Change [Abstract]
CO2 produced per year (in millions of tons) | T	21
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	$ 83.8
Estimate Of Environmental Capital Expenditures In Two Years	30.1
Estimate Of Environmental Capital Expenditures In Three Years	14.4
Estimate Of Environmental Capital Expenditures In Four Years	87.3
Estimate Of Environmental Capital Expenditures In Five Years	$ 130
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) - MPS Merchant Services, Inc. [Member] $ in Millions	9 Months Ended
	Sep. 30, 2016USD ($)
Loss Contingencies [Line Items]
Approximate amount of refunds received as a net purchaser of power through settlements with sellers of power	$ 8
Estimated additional refunds entitled to receive	$ 12

Related Party Transactions an64

Related Party Transactions and Relationships (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Kansas City Power and Light Company [Member] | Money Pool [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 11,100,000		$ 11,100,000		$ 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	71,500,000		71,500,000		50,000,000
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	48,900,000	$ 45,500,000	143,800,000	$ 137,700,000
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	$ 19,500,000		$ 19,500,000		$ 15,800,000
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%		18.00%

Derivative Instruments (Details

Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Futures contracts [Member] | Not Designated as Hedging Instrument [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	$ 14.9		$ 26.6
Fair Value	0		(5.7)
Forward Contracts [Member] | Not Designated as Hedging Instrument [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	11.1		15.6
Fair Value	2.6		3.1
Transmission Congestion Rights [Member] | Not Designated as Hedging Instrument [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	5.1		5.6
Fair Value	0.7		(0.5)
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	4,415	$ 4,400	0
Fair Value	$ (78.8)		0
Kansas City Power and Light Company [Member]
Price Risk Derivatives [Abstract]
Percentage Of Expected Summer Month Natural Gas Generation For Missouri Jurisdictional Retail Sales Hedged Year Two	20.00%
Percentage Of Expected Summer Month Natural Gas Generation For Missouri Jurisdictional Retail Sales Hedged Year Three	7.00%
Kansas City Power and Light Company [Member] | Futures contracts [Member] | Not Designated as Hedging Instrument [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	$ 0.2		0.9
Fair Value	0		(0.1)
Kansas City Power and Light Company [Member] | Transmission Congestion Rights [Member] | Not Designated as Hedging Instrument [Member]
Price Risk Derivatives [Abstract]
Notional Contract Amount	3.9		4.1
Fair Value	$ 0.4		$ (0.4)
KCPL Greater Missouri Operations [Member]
Price Risk Derivatives [Abstract]
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged remainder of fiscal year	66.00%
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged year two	37.00%
Percentage of expected on peak natural gas and natural gas equivalent purchased power price exposure hedged year three	12.00%

Derivative Instruments Cash Flo

Derivative Instruments Cash Flow Hedge (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016USD ($)
Derivative [Line Items]
Cash Flow Hedge Loss to be Reclassified within Twelve Months	$ 8.9
Kansas City Power and Light Company [Member]
Derivative [Line Items]
Cash Flow Hedge Loss to be Reclassified within Twelve Months	$ 8.5

Derivative Instruments Offsetti

Derivative Instruments Offsetting Assets (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 5.3	$ 3.3
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(2)	(0.2)
Derivative Asset	3.3	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	3.3	3.1
Kansas City Power and Light Company [Member]
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset	1.1	0.2
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	(0.7)	(0.2)
Derivative Asset	0.4	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	$ 0.4	$ 0

Derivative Instruments Offset68

Derivative Instruments Offsetting Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 80.8	$ 6.4
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(2)	(5.9)
Derivative Liability	78.8	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	78.8	0.5
Cash collateral posted with counterparties	0.1	5.7
Kansas City Power and Light Company [Member]
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability	0.7	0.7
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	(0.7)	(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	Sep. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 5.3	$ 3.3
Derivative Liability, Fair Value, Gross Liability	80.8	6.4
Kansas City Power and Light Company [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1.1	0.2
Derivative Liability, Fair Value, Gross Liability	0.7	0.7
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member] | Other Balance Sheet Location [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	5.3
Derivative Liability, Fair Value, Gross Liability	2
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	1.1	0.2
Derivative Liability, Fair Value, Gross Liability	0.7	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		3.3
Derivative Liability, Fair Value, Gross Liability		$ 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	0
Derivative Liability, Fair Value, Gross Liability	$ 78.8

Derivative Instruments Gain and

Derivative Instruments Gain and Losses (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
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	$ 0.3	$ (2.4)	$ (80.7)	$ (15.6)
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	(1.9)	(0.1)	(5.1)
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	(0.3)	0	0.9	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	2.4	0.8	2.4	(6.7)
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	0.1	(0.1)	0	(0.1)
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	0	0	0.5	0
Purchased Power Costs [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	0.5	(0.2)	0.2	(1.4)
Fuel Costs [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)	(0.1)	(4.6)	(1.2)
Fuel Costs [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	0.3	1.1	0.2	1.3
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	2	(0.2)	1.7	(7.9)
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	2	(0.2)	1.7	(7.9)
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	$ (1.8)	$ 0	$ (78.8)	$ 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	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net asset (liability) at beginning of period	$ (76.1)	$ 0.8	$ (0.1)	$ 3.5
Purchases	0	(0.2)	(0.5)	0.4
Settlements	(6.4)	(2.9)	(9)	(1)
Net asset (liability) at September 30	(77.8)	0.4	(77.8)	0.4
Purchased Power Costs [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	0.5	(0.2)	0.2	(1.4)
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	3.8	3.2	7.9	6.9
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end			0.1	(0.1)
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	2	(0.2)	1.7	(7.9)
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	0	(0.1)	0	(0.1)
Interest Charges [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	(1.8)	0	(78.8)	0
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	(1.8)	0	(78.8)	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	0.2	(0.1)	0.8	(0.1)
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	0.8	(0.1)	0.8	(0.1)
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	0.5	0.1	(0.4)	3.1
Purchases	(0.1)	(0.2)	(0.5)	(0.4)
Settlements	(2)	0.2	(0.9)	5.1
Net asset (liability) at September 30	0.4	(0.2)	0.4	(0.2)
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	2	(0.2)	1.7	(7.9)
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	0	(0.1)	0	(0.1)
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			0.5	(0.1)
Total unrealized gains and (losses) relating to assets and liabilities still on the consolidated balance sheet at period end	0.5	(0.1)	$ 0.5	$ (0.1)
Kansas City Power and Light Company [Member] | Regulatory Asset [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	$ 0	$ (0.1)

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Long-Term Debt (Details) - USD ($) $ in Billions	Sep. 30, 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	4.1	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	$ 2.8	$ 2.8

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Millions	Sep. 30, 2016USD ($)	Dec. 31, 2015USD ($)
Assets [Abstract]
Derivative instruments, assets	$ 5.3	$ 3.3
Liabilities [Abstract]
Derivative instruments, liabilities	80.8	6.4
Kansas City Power and Light Company [Member]
Assets [Abstract]
Derivative instruments, assets	1.1	0.2
Liabilities [Abstract]
Derivative instruments, liabilities	0.7	0.7
Other Consolidated Entities [Member] | Fixed Income Funds [Member]
SERP rabbi trust [Abstract]
Alternative Investments, Fair Value Disclosure	16.7	16.6
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Derivative instruments, assets	5.3	3.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	218.3	200.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	13.7	13.6
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1	0.1
Total assets	237.4	217.7
Liabilities [Abstract]
Derivative instruments, liabilities	80.8	6.4
Total liabilities	80.8	6.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	1.1	0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	178.7	165.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.9	6.3
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1	0.1
Total assets	188.8	171.8
Liabilities [Abstract]
Derivative instruments, liabilities	1.1	5.7
Total liabilities	1.1	5.7
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	2.3	2.7
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	39.6	35.3
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	4.8	7.3
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0	0
Total assets	46.7	45.3
Liabilities [Abstract]
Derivative instruments, liabilities	0	0
Total liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	1.9	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	0
Total assets	1.9	0.6
Liabilities [Abstract]
Derivative instruments, liabilities	79.7	0.7
Total liabilities	79.7	0.7
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member]
Assets [Abstract]
Derivative instruments, assets	1.1	0.2
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	218.3	200.7
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	13.7	13.6
SERP rabbi trust [Abstract]
Total assets	233.1	214.5
Liabilities [Abstract]
Derivative instruments, liabilities	0.7	0.7
Total liabilities	0.7	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	147.4	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	29.7	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	1.8	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	3.1	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	34.4	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	0.3	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	1.6	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	8	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	178.7	165.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.9	6.3
SERP rabbi trust [Abstract]
Total assets	187.6	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	147.4	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	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	29.7	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	1.6	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	8	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	39.6	35.3
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	4.8	7.3
SERP rabbi trust [Abstract]
Total assets	44.4	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	4.8	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	1.8	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	3.1	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	34.4	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	0.3	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	1.1	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	1.1	0.2
Liabilities [Abstract]
Derivative instruments, liabilities	0.7	0.6
Total liabilities	0.7	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	4.2	3.1
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1	0.1
Total assets	4.3	3.2
Liabilities [Abstract]
Derivative instruments, liabilities	80.1	5.7
Total liabilities	80.1	5.7
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Commodity Contract [Member]
Liabilities [Abstract]
Derivative instruments, liabilities	1.3
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Interest Rate Contract [Member]
Liabilities [Abstract]
Derivative instruments, liabilities	$ 78.8
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	$ 1.1	0
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0.1	0.1
Total assets	1.2	0.1
Liabilities [Abstract]
Derivative instruments, liabilities	1.1	5.6
Total liabilities	1.1	5.6
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 1 [Member] | Commodity Contract [Member]
Liabilities [Abstract]
Derivative instruments, liabilities	1.1
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Contract [Member]
Liabilities [Abstract]
Derivative instruments, liabilities	0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	2.3	2.7
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0	0
Total assets	2.3	2.7
Liabilities [Abstract]
Derivative instruments, liabilities	0	0
Total liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 2 [Member] | Commodity Contract [Member]
Liabilities [Abstract]
Derivative instruments, liabilities	0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Contract [Member]
Liabilities [Abstract]
Derivative instruments, liabilities	0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	0.8	0.4
SERP rabbi trust [Abstract]
SERP Rabbi Trusts, Fair Value Disclosure	0	0
Total assets	0.8	0.4
Liabilities [Abstract]
Derivative instruments, liabilities	79	0.1
Total liabilities	79	$ 0.1
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member]
Liabilities [Abstract]
Derivative instruments, liabilities	0.2
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Contract [Member]
Liabilities [Abstract]
Derivative instruments, liabilities	$ 78.8

Accumulated Other Comprehensi74

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (12)	$ (18.7)
Amounts reclassified from accumulated other comprehensive loss			4.5	4.5
Net current period other comprehensive income	$ 1.5	$ 1.4	4.5	4.5
Ending balance	(7.5)	(14.2)	(7.5)	(14.2)
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)
Amounts reclassified from accumulated other comprehensive loss			4.1	4.2
Net current period other comprehensive income			4.1	4.2
Ending balance	(6)	(11.6)	(6)	(11.6)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(1.9)	(2.9)
Amounts reclassified from accumulated other comprehensive loss			0.4	0.3
Net current period other comprehensive income			0.4	0.3
Ending balance	(1.5)	(2.6)	(1.5)	(2.6)
Kansas City Power and Light Company [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(9.6)
Net current period other comprehensive income	1.2	1.3	4	4
Ending balance	(5.6)		(5.6)
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			4	4
Net current period other comprehensive income			4	4
Ending balance	$ (5.6)	$ (10.9)	$ (5.6)	$ (10.9)

Accumulated Other Comprehensi75

Accumulated Other Comprehensive Income (Loss) Reclassification (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	$ (67.6)	$ (51)	$ (251.7)	$ (148.3)
Fuel	(105.7)	(124.5)	(285.7)	(332)
Utility operating and maintenance expenses	(193.3)	(182.5)	(553.1)	(537.4)
Income before income tax expense and income from equity investments	215.6	205.2	301.4	298.8
Income tax benefit	(82.7)	(78.6)	(111.5)	(109.6)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(1.5)	(1.4)	(4.5)	(4.5)
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	(2.3)	(2.3)	(6.9)	(6.9)
Income tax benefit	1	0.9	2.8	2.7
Net income	(1.3)	(1.4)	(4.1)	(4.2)
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	(2.3)	(2.3)	(6.9)	(6.9)
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	(0.2)	(0.1)	(0.6)	(0.5)
Income before income tax expense and income from equity investments	(0.2)	(0.1)	(0.6)	(0.5)
Income tax benefit	0	0.1	0.2	0.2
Net income	(0.2)	0	(0.4)	(0.3)
Kansas City Power and Light Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest charges	(34.7)	(34.8)	(104.9)	(100.4)
Fuel	(77)	(89.4)	(205.6)	(237.3)
Utility operating and maintenance expenses	(131.9)	(122.9)	(379.6)	(365.8)
Income before income tax expense and income from equity investments	186.2	134.8	324.7	195.6
Income tax benefit	(68.5)	(50.5)	(116.5)	(68.7)
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	(2.2)	(2.2)	(6.6)	(6.6)
Income tax benefit	1	0.9	2.6	2.6
Net income	(1.2)	(1.3)	(4)	(4)
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	$ (2.2)	$ (2.2)	$ (6.6)	$ (6.6)

Income Tax Expense (Details)

Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Current income taxes
Federal	$ 0	$ (0.8)	$ (0.1)	$ (0.3)
State	0	0.5	0.3	0.4
Total	0	(0.3)	0.2	0.1
Deferred income taxes
Federal	70.1	66.4	91.5	91.8
State	13	12.4	18.4	18.3
Total	83.1	78.8	109.9	110.1
Investment tax credit
Deferral	0	0.5	2.5	0.5
Amortization	(0.4)	(0.4)	(1.1)	(1.1)
Total	(0.4)	0.1	1.4	(0.6)
Total income tax expense	$ 82.7	$ 78.6	$ 111.5	$ 109.6
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	(0.30%)	0.30%	(0.20%)	0.40%
Amortization of investments tax credits (in hundredths)	(0.20%)	(0.20%)	(0.40%)	(0.40%)
Federal income tax credits (in hundredths)	(1.10%)	(1.20%)	(2.70%)	(2.60%)
State income taxes (in hundredths)	3.90%	4.20%	4.00%	4.00%
Transaction costs (in hundredths)	1.00%	0.00%	1.00%	0.00%
Other (in hundredths)	(0.10%)	0.20%	0.00%	0.20%
Effective income tax rate (in hundredths)	38.20%	38.30%	36.70%	36.60%
Kansas City Power and Light Company [Member]
Current income taxes
Federal	$ 35.4	$ 43.9	$ 36.6	$ 42.4
State	6.4	7.1	6.7	6.7
Total	41.8	51	43.3	49.1
Deferred income taxes
Federal	22.5	(1.6)	61.5	14.6
State	4.5	0.8	12.5	5.2
Total	27	(0.8)	74	19.8
Investment tax credit
Deferral	0	0.5	0	0.5
Amortization	(0.3)	(0.2)	(0.8)	(0.7)
Total	(0.3)	0.3	(0.8)	(0.2)
Total income tax expense	$ 68.5	$ 50.5	$ 116.5	$ 68.7
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax (in hundredths)	35.00%	35.00%	35.00%	35.00%
Differences between book and tax depreciation not normalized (in hundredths)	(0.50%)	0.40%	(0.30%)	0.60%
Amortization of investments tax credits (in hundredths)	(0.10%)	(0.20%)	(0.20%)	(0.40%)
Federal income tax credits (in hundredths)	(1.20%)	(1.80%)	(2.30%)	(3.90%)
State income taxes (in hundredths)	3.80%	3.90%	3.80%	3.90%
Other (in hundredths)	(0.20%)	0.10%	(0.10%)	(0.10%)
Effective income tax rate (in hundredths)	36.80%	37.40%	35.90%	35.10%

Segments and Related Informat77

Segments and Related Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating revenues	$ 856.8	$ 781.4	$ 2,099.7	$ 1,939.5
Depreciation and amortization	(86.4)	(82.4)	(256.9)	(245.7)
Interest (charges) income	(67.6)	(51)	(251.7)	(148.3)
Income tax (expense) benefit	(82.7)	(78.6)	(111.5)	(109.6)
Net income (loss)	133.6	126.8	192	190.1
Assets	11,044.7		11,044.7		$ 10,738.6
Capital expenditures			435.3	520.9	677.1
Operating Segments [Member] | Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	856.8	781.4	2,099.7	1,939.5
Depreciation and amortization	(86.4)	(82.4)	(256.9)	(245.7)
Interest (charges) income	(49.3)	(48.9)	(147.4)	(142.1)
Income tax (expense) benefit	(95.9)	(78.5)	(160.2)	(112)
Net income (loss)	161.1	129.1	278.4	196.4
Assets	11,337.1		11,337.1		11,045.5
Capital expenditures			435.3		677.1
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Depreciation and amortization	0	0	0	0
Interest (charges) income	(26.4)	(10.2)	(128.4)	(30.3)
Income tax (expense) benefit	13.2	(0.1)	48.7	2.4
Net income (loss)	(27.5)	(2.3)	(86.4)	(6.3)
Assets	114.5		114.5		(51.1)
Capital expenditures			0		0
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Depreciation and amortization	0	0	0	0
Interest (charges) income	8.1	8.1	24.1	24.1
Income tax (expense) benefit	0	0	0	0
Net income (loss)	0	$ 0	0	$ 0
Assets	$ (406.9)		(406.9)		(255.8)
Capital expenditures			$ 0		$ 0