Consolidated Statements of Common Shareholders' Equity and Noncontrolling Interest (Unaudited) (USD $) In Millions, except Share data	Total	KANSAS CITY POWER AND LIGHT CO [Member]	Common Stock [Member]	Common Stock [Member] KANSAS CITY POWER AND LIGHT CO [Member]	Retained Earnings [Member]	Retained Earnings [Member] KANSAS CITY POWER AND LIGHT CO [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member] KANSAS CITY POWER AND LIGHT CO [Member]	Total Common Shareholders' Equity [Member]	Total Common Shareholders' Equity [Member] KANSAS CITY POWER AND LIGHT CO [Member]	Noncontrolling Interest [Member]
Beginning balance (in shares) at Dec. 31, 2009			135,636,538	1			(213,423)
Beginning balance at Dec. 31, 2009			$ 2,313.7	$ 1,563.1	$ 529.2	$ 410.1	$ (5.5)	$ (44.9)	$ (41.5)			$ 1.2
Net income attributable to Great Plains Energy	216.6				216.6	160.0
Issuance of common stock			5.1
Issuance of common stock (in shares)			269,855
Issuance of restricted common stock			2.3
Issuance of restricted common stock (in shares)			130,137
Equity compensation expense, net of forfeitures	3.4	2.4	1.1
Unearned Compensation
Issuance of restricted common stock, unearned compensation			(2.3)
Forfeiture of restricted common stock			0.6
Compensation expense recognized			1.9
Other			0.1
Loss on reissuance of treasury stock					0
Dividends:
Common stock					(84.4)	(70.0)
Preferred stock - at required rates					(1.2)
Performance shares					(0.2)
Treasury shares acquired							(3.1)
Treasury shares acquired (in shares)							(172,913)
Treasury shares reissued							0
Treasury shares reissued (in shares)							917
Derivative hedging activity, net of tax	(15.0)	3.7						(15.0)	3.7
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 Sep. 30, 2010			136,036,530	1			(385,419)
Ending balance at Sep. 30, 2010			2,322.5	1,563.1	660.0	500.1	(8.6)	(59.8)	(37.8)	2,914.1	2,025.4	1.2
Beginning balance at Jun. 30, 2010
Net income attributable to Great Plains Energy	132.0
Equity compensation expense, net of forfeitures	0.8	0.6
Dividends:
Derivative hedging activity, net of tax	(4.3)	1.4
Change in unrecognized pension expense, net of tax	0
Ending balance (in shares) at Sep. 30, 2010				1
Ending balance at Sep. 30, 2010				1,563.1						2,914.1	2,025.4
Beginning balance (in shares) at Dec. 31, 2010			136,113,954	1			(400,889)
Beginning balance at Dec. 31, 2010			2,324.4	1,563.1	626.5	478.3	(8.9)	(56.1)	(36.4)			1.2
Net income attributable to Great Plains Energy	172.3				172.3	122.8
Issuance of common stock			4.5
Issuance of common stock (in shares)			226,691
Issuance of restricted common stock			0
Issuance of restricted common stock (in shares)			0
Equity compensation expense, net of forfeitures	4.5	3.1	0.2
Unearned Compensation
Issuance of restricted common stock, unearned compensation			(3.5)
Forfeiture of restricted common stock			0.9
Compensation expense recognized			1.7
Other			0.3
Loss on reissuance of treasury stock					(0.7)
Dividends:
Common stock					(84.7)	(75.0)
Preferred stock - at required rates					(1.2)
Performance shares					(0.3)
Treasury shares acquired							(2.3)
Treasury shares acquired (in shares)							(125,024)
Treasury shares reissued							5.6
Treasury shares reissued (in shares)							259,024
Derivative hedging activity, net of tax	4.0	3.9						4.0	3.9
Change in unrecognized pension expense, net of tax	0.1							0.1
Net income attributable to noncontrolling interest												0
Distribution												0
Ending balance (in shares) at Sep. 30, 2011			136,340,645	1			(266,889)
Ending balance at Sep. 30, 2011			2,328.5	1,563.1	711.9	526.1	(5.6)	(52.0)	(32.5)	2,982.8	2,056.7	1.2
Beginning balance at Jun. 30, 2011
Net income attributable to Great Plains Energy	126.5
Equity compensation expense, net of forfeitures	1.2	0.8
Dividends:
Derivative hedging activity, net of tax	3.1	1.3
Change in unrecognized pension expense, net of tax	0
Ending balance (in shares) at Sep. 30, 2011				1
Ending balance at Sep. 30, 2011				$ 1,563.1						$ 2,982.8	$ 2,056.7