Segments and Related Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended			12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Operating revenues	$ 746.2	$ 773.7	$ 1,829.5		$ 1,831.7
Depreciation and amortization	(68.9)	(65.9)	(204.2)		(205.9)
Interest charges	(48.1)	(60.8)	(170.8)		(156.0)
Income tax (expense) benefit	(82.6)	(75.4)	(104.9)		(90.6)
Net income (loss) attributable to Great Plains Energy	146.2	126.5	195.2		172.3
Assets	9,502.4		9,502.4			9,118.0
Capital expenditures			409.5	[1]		456.6	[1]
All Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0		0
Depreciation and amortization	0	0	0		0
Interest charges	0.3	(10.6)	(21.3)		(31.2)
Income tax (expense) benefit	3.9	7.5	15.7		19.2
Net income (loss) attributable to Great Plains Energy	4.3	(7.4)	(15.0)		(17.6)
Assets	152.5		152.5			51.9
Capital expenditures			0	[1]		0	[1]
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Assets	(415.4)		(415.4)			(417.3)
Capital expenditures			0	[1]		0	[1]
Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	746.2	773.7	1,829.5		1,831.7
Depreciation and amortization	(68.9)	(65.9)	(204.2)		(205.9)
Interest charges	(48.4)	(50.2)	(149.5)		(124.8)
Income tax (expense) benefit	(86.5)	(82.9)	(120.6)		(109.8)
Net income (loss) attributable to Great Plains Energy	141.9	133.9	210.2		189.9
Assets	9,765.3		9,765.3			9,483.4
Capital expenditures			$ 409.5	[1]		$ 456.6	[1]

[1] Capital expenditures reflect year to date amounts for the periods presented.