Consolidated Statements of Common Shareholders' Equity and Noncontrolling Interest (unaudited) (USD $) In Millions, except Share data, unless otherwise specified	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]	Noncontrolling Interest [Member]
Beginning balance at Dec. 31, 2010			$ 2,324.4	$ 1,563.1	$ 626.5	$ 478.3	$ (8.9)	$ (56.1)	$ (36.4)	$ 1.2
Beginning balance (in shares) at Dec. 31, 2010			136,113,954	1			(400,889)
Distribution										0
Total Great Plains Energy Common Shareholders' Equity	2,879.7	1,995.0
Derivative hedging activity, net of tax	0.9	2.6						0.9	2.6
Change in unrecognized pension expense, net of tax	0.1							0.1
Net income (loss) attributable to Great Plains Energy	45.8				45.8	37.4
Loss On Reissuance Of Treasury Stock					(0.5)
Treasury shares acquired							(2.2)
Treasury shares acquired (in shares)							(88,400)
Treasury shares reissued							4.8
Treasury shares reissued (in shares)							221,296
Issuance of common stock			3.1
Issuance of common stock (in shares)			155,345
Equity compensation expense, net of forfeitures			0.1
Unearned Compensation [Abstract]
Issuance of restricted common stock			(2.9)
Forfeiture of restricted common stock			0.8
Compensation expense recognized			1.2
Stockholders' Equity, Other			0.1
Dividends:
Common stock					(56.4)	(50.0)
Preferred stock - at required rates					(0.8)
Performance shares					(0.3)
Net income attributable to noncontrolling interest										(0.1)
Ending balance at Jun. 30, 2011			2,326.8	1,563.1	614.3	465.7	(6.3)	(55.1)	(33.8)	1.1
Ending balance (in shares) at Jun. 30, 2011			136,269,299	1			(267,993)
Beginning balance at Mar. 31, 2011
Total Great Plains Energy Common Shareholders' Equity	2,879.7	1,995.0
Derivative hedging activity, net of tax	(1.2)	1.3
Change in unrecognized pension expense, net of tax	0.1
Net income (loss) attributable to Great Plains Energy	43.4
Ending balance at Jun. 30, 2011				1,563.1
Ending balance (in shares) at Jun. 30, 2011				1
Beginning balance at Dec. 31, 2011			2,330.6	1,563.1	684.7	513.8	(5.6)	(49.8)	(31.4)	1.0
Beginning balance (in shares) at Dec. 31, 2011			136,406,306	1			(264,567)
Distribution										(0.6)
Total Great Plains Energy Common Shareholders' Equity	3,247.0	2,044.1
Derivative hedging activity, net of tax	6.1	2.6						6.1	2.6
Change in unrecognized pension expense, net of tax	0.1							0.1
Net income (loss) attributable to Great Plains Energy	49.0				49.0	46.0
Loss On Reissuance Of Treasury Stock					(0.3)
Treasury shares acquired							(2.9)
Treasury shares acquired (in shares)							(145,701)
Treasury shares reissued							3.5
Treasury shares reissued (in shares)							169,800
Issuance of common stock			290.3
Issuance of common stock (in shares)			17,248,954
Equity compensation expense, net of forfeitures			0.1
Unearned Compensation [Abstract]
Issuance of restricted common stock			(3.2)
Forfeiture of restricted common stock			1.0
Compensation expense recognized			1.6
Stockholders' Equity, Other			0.5
Dividends:
Common stock					(57.9)	(50.0)
Preferred stock - at required rates					(0.8)
Performance shares					0
Net income attributable to noncontrolling interest										(0.2)
Ending balance at Jun. 30, 2012			2,620.9	1,563.1	674.7	509.8	(5.0)	(43.6)	(28.8)	0.2
Ending balance (in shares) at Jun. 30, 2012			153,655,260	1			(240,468)
Beginning balance at Mar. 31, 2012
Total Great Plains Energy Common Shareholders' Equity	3,247.0	2,044.1
Derivative hedging activity, net of tax	3.2	1.4
Change in unrecognized pension expense, net of tax	0
Net income (loss) attributable to Great Plains Energy	58.1
Ending balance at Jun. 30, 2012				$ 1,563.1
Ending balance (in shares) at Jun. 30, 2012				1