Segments and Related Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Jan. 02, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Operating revenues	$ 486.3	$ 773.7	$ 565.1	$ 492.9	$ 467.8	$ 728.8	$ 552.0	$ 506.9	$ 2,318.0	$ 2,255.5	$ 1,965.0
Depreciation and amortization									(273.1)	(331.6)	(302.2)
Interest charges									(218.4)	(184.8)	(180.9)
Income tax (expense) benefit									(84.8)	(99.0)	(29.5)
Discontinued operations									0	0	(1.5)
Net income (loss) attributable to Great Plains Energy	2.1	126.5	43.4	2.4	(4.9)	132.0	64.3	20.3	174.4	211.7	150.1
Assets	9,118.0				8,818.2				9,118.0	8,818.2		8,482.8
Utility capital expenditures									456.6	618.1	841.3
All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues									0	0	0
Depreciation and amortization									0	0	0
Interest charges									(41.5)	(41.7)	(29.9)
Income tax (expense) benefit									24.5	24.3	34.1
Discontinued operations									0	0	(1.5)
Net income (loss) attributable to Great Plains Energy									(25.5)	(23.6)	(7.7)
Assets	51.9				66.3				51.9	66.3		152.5
Utility capital expenditures									0	0	0
Corporate Elimination [Member]
Segment Reporting Information [Line Items]
Assets	(417.3)				(400.8)				(417.3)	(400.8)		(435.0)
Utility capital expenditures									0	0	0
Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues									2,318.0	2,255.5	1,965.0
Depreciation and amortization									(273.1)	(331.6)	(302.2)
Interest charges									(176.9)	(143.1)	(151.0)
Income tax (expense) benefit									(109.3)	(123.3)	(63.6)
Discontinued operations									0	0	0
Net income (loss) attributable to Great Plains Energy									199.9	235.3	157.8
Assets	9,483.4				9,152.7				9,483.4	9,152.7		8,765.3
Utility capital expenditures									$ 456.6	$ 618.1	$ 841.3