Consolidated Statements of Common Shareholders' Equity and Noncontrolling Interest (Unaudited) (USD $) In Millions, except Share data	Total	Great Plains Energy Incorporated [Member]	Great Plains Energy Incorporated [Member] Common Stock [Member]	Great Plains Energy Incorporated [Member] Retained Earnings [Member]	Great Plains Energy Incorporated [Member] Treasury Stock [Member]	Great Plains Energy Incorporated [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Great Plains Energy Incorporated [Member] Total Common Shareholders' Equity [Member]	Great Plains Energy Incorporated [Member] Noncontrolling Interest [Member]	KANSAS CITY POWER AND LIGHT CO [Member]	KANSAS CITY POWER AND LIGHT CO [Member] Common Stock [Member]	KANSAS CITY POWER AND LIGHT CO [Member] Retained Earnings [Member]	KANSAS CITY POWER AND LIGHT CO [Member] Accumulated Other Comprehensive Income (Loss) [Member]	KANSAS CITY POWER AND LIGHT CO [Member] Total Common Shareholders' Equity [Member]
Beginning balance (in shares) at Dec. 31, 2009			135,636,538		(213,423)					1
Beginning balance at Dec. 31, 2009			$ 2,313.7	$ 529.2	$ (5.5)	$ (44.9)		$ 1.2		$ 1,563.1	$ 410.1	$ (41.5)
Net income attributable to Great Plains Energy	84.6	84.6		84.6							67.4
Issuance of common stock			3.5
Issuance of common stock (in shares)			189,275
Issuance of restricted common stock			1.8
Issuance of restricted common stock (in shares)			103,211
Equity compensation expense, net of forfeitures	2.6		0.6						1.8
Unearned Compensation
Issuance of restricted common stock, unearned compensation			(1.8)
Forfeiture of restricted common stock			0.6
Compensation expense recognized			1.7
Other			0
Loss on reissuance of treasury stock				0
Dividends:
Common stock				(56.2)							(45.0)
Preferred stock - at required rates				(0.8)
Performance shares				(0.2)
Treasury shares acquired					(2.8)
Treasury shares acquired (in shares)					(157,308)
Treasury shares reissued					0
Treasury shares reissued (in shares)					917
Derivative hedging activity, net of tax		(10.7)				(10.7)			2.3			2.3
Change in unrecognized pension expense, net of tax		0.1				0.1
Net income attributable to noncontrolling interest								0.1
Distribution								(0.1)
Ending balance (in shares) at Jun. 30, 2010			135,929,024		(369,814)					1
Ending balance at Jun. 30, 2010			2,320.1	556.6	(8.3)	(55.5)	2,812.9	1.2		1,563.1	432.5	(39.2)	1,956.4
Beginning balance at Mar. 31, 2010
Net income attributable to Great Plains Energy	64.3	64.3
Equity compensation expense, net of forfeitures	2.3								1.6
Dividends:
Derivative hedging activity, net of tax		(7.4)							1.2
Change in unrecognized pension expense, net of tax		0.1
Ending balance (in shares) at Jun. 30, 2010										1
Ending balance at Jun. 30, 2010							2,812.9			1,563.1			1,956.4
Beginning balance (in shares) at Dec. 31, 2010			136,113,954		(400,889)					1
Beginning balance at Dec. 31, 2010			2,324.4	626.5	(8.9)	(56.1)		1.2		1,563.1	478.3	(36.4)
Net income attributable to Great Plains Energy	45.8	45.8		45.8							37.4
Issuance of common stock			3.1
Issuance of common stock (in shares)			155,345
Issuance of restricted common stock			0
Issuance of restricted common stock (in shares)			0
Equity compensation expense, net of forfeitures	3.3		0.1						2.3
Unearned Compensation
Issuance of restricted common stock, unearned compensation			(2.9)
Forfeiture of restricted common stock			0.8
Compensation expense recognized			1.2
Other			0.1
Loss on reissuance of treasury stock				(0.5)
Dividends:
Common stock				(56.4)							(50.0)
Preferred stock - at required rates				(0.8)
Performance shares				(0.3)
Treasury shares acquired					(2.2)
Treasury shares acquired (in shares)					(88,400)
Treasury shares reissued					4.8
Treasury shares reissued (in shares)					221,296
Derivative hedging activity, net of tax		0.9				0.9			2.6			2.6
Change in unrecognized pension expense, net of tax		0.1				0.1
Net income attributable to noncontrolling interest								(0.1)
Distribution								0
Ending balance (in shares) at Jun. 30, 2011			136,269,299		(267,993)					1
Ending balance at Jun. 30, 2011			2,326.8	614.3	(6.3)	(55.1)	2,879.7	1.1		1,563.1	465.7	(33.8)	1,995.0
Beginning balance at Mar. 31, 2011
Net income attributable to Great Plains Energy	43.4	43.4
Equity compensation expense, net of forfeitures	1.7								1.2
Dividends:
Derivative hedging activity, net of tax		(1.2)							1.3
Change in unrecognized pension expense, net of tax		0.1
Ending balance (in shares) at Jun. 30, 2011										1
Ending balance at Jun. 30, 2011							$ 2,879.7			$ 1,563.1			$ 1,995.0