Segments and Related Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended			12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 600.3	$ 603.6	$ 1,142.5		$ 1,083.3
Depreciation and amortization	(72.6)	(67.9)	(142.8)		(135.3)
Interest charges	(49.4)	(55.8)	(99.1)		(122.7)
Income tax (expense) benefit	(32.7)	(31.8)	(44.2)		(22.3)
Net income (loss) attributable to Great Plains Energy	63.6	58.1	89.6		49.0
Assets, Total	9,764.0		9,764.0			9,647.3
Capital expenditures			339.8	[1]		610.2	[1]
Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	600.3	603.6	1,142.5		1,083.3
Depreciation and amortization	(72.6)	(67.9)	(142.8)		(135.3)
Interest charges	(47.4)	(50.4)	(95.2)		(101.1)
Income tax (expense) benefit	(33.9)	(35.9)	(46.5)		(34.1)
Net income (loss) attributable to Great Plains Energy	65.5	63.8	93.1		68.3
Assets, Total	10,124.6		10,124.6			9,910.6
Capital expenditures			339.8	[1]		610.2	[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	(14.6)	(15.1)	(29.1)		(40.2)
Income tax (expense) benefit	1.2	4.1	2.3		11.8
Net income (loss) attributable to Great Plains Energy	(1.9)	(5.7)	(3.5)		(19.3)
Assets, Total	63.9		63.9			122.4
Capital expenditures			0	[1]		0	[1]
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0		0
Depreciation and amortization	0	0	0		0
Interest charges	12.6	9.7	25.2		18.6
Income tax (expense) benefit	0	0	0		0
Net income (loss) attributable to Great Plains Energy	0	0	0		0
Assets, Total	(424.5)		(424.5)			(385.7)
Capital expenditures			$ 0	[1]		$ 0	[1]

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