Segments and Related Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended			12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 765.0	$ 746.2	$ 1,907.5		$ 1,829.5
Depreciation and amortization	(73.3)	(68.9)	(216.1)		(204.2)
Interest charges	(48.9)	(48.1)	(148.0)		(170.8)
Income tax (expense) benefit	(81.8)	(82.6)	(126.0)		(104.9)
Net income (loss) attributable to Great Plains Energy	143.1	146.2	232.7		195.2
Assets, Total	9,869.2		9,869.2			9,647.3
Capital expenditures			486.2	[1]	409.5	610.2	[1]
Electric Utility Segment [Member] | Electric Utility Segment [Member]
Segment Reporting Information [Line Items]
Operating revenues	765.0	746.2	1,907.5		1,829.5
Depreciation and amortization	(73.3)	(68.9)	(216.1)		(204.2)
Interest charges	(46.7)	(48.4)	(141.9)		(149.5)
Income tax (expense) benefit	(83.6)	(86.5)	(130.1)		(120.6)
Net income (loss) attributable to Great Plains Energy	145.4	141.9	238.5		210.2
Assets, Total	10,193.9		10,193.9			9,910.6
Capital expenditures			486.2	[1]		610.2	[1]
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0		0
Depreciation and amortization	0	0	0		0
Interest charges	(13.6)	(12.3)	(42.7)		(52.5)
Income tax (expense) benefit	1.8	3.9	4.1		15.7
Net income (loss) attributable to Great Plains Energy	(2.3)	4.3	(5.8)		(15.0)
Assets, Total	87.8		87.8			122.4
Capital expenditures			0	[1]		0	[1]
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0		0
Depreciation and amortization	0	0	0		0
Interest charges	11.4	12.6	36.6		31.2
Income tax (expense) benefit	0	0	0		0
Net income (loss) attributable to Great Plains Energy	0	0	0		0
Assets, Total	(412.5)		(412.5)			(385.7)
Capital expenditures			$ 0	[1]		$ 0	[1]

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