Schedule II Valuation and Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 6.9		$ 6.8		$ 7.0
Additions charged to costs and expenses	12.3		12.0		13.7
Additions charged to other accounts	7.6	[1]	7.8	[1]	6.9	[1]
Deductions	24.3	[2]	19.7	[2]	20.8	[2]
Balance at end of period	2.5		6.9		6.8
Allowance for Doubtful Accounts [Member] | Kansas City Power and Light Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	1.5		1.4		1.5
Additions charged to costs and expenses	8.0		7.9		8.8
Additions charged to other accounts	5.0	[1]	5.2	[1]	4.5	[1]
Deductions	13.4	[2]	13.0	[2]	13.4	[2]
Balance at end of period	1.1		1.5		1.4
Legal Reserve [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	4.6		6.7		10.2
Additions charged to costs and expenses	2.7		(0.2)		(0.1)
Additions charged to other accounts	0		0		0
Deductions	2.7	[3]	1.9	[3]	3.4	[3]
Balance at end of period	4.6		4.6		6.7
Legal Reserve [Member] | Kansas City Power and Light Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	2.9		3.9		3.0
Additions charged to costs and expenses	0.9		0.5		1.3
Additions charged to other accounts	0		0		0
Deductions	0.9	[3]	1.5	[3]	0.4	[3]
Balance at end of period	2.9		2.9		3.9
Reserve for Environmental Costs [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	2.3		2.5		2.5
Additions charged to costs and expenses	0		0		0
Additions charged to other accounts	0		0		0
Deductions	0.6		0.2		0
Balance at end of period	1.7		2.3		2.5
Reserve for Environmental Costs [Member] | Kansas City Power and Light Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	0.3		0.3		0.3
Additions charged to costs and expenses	0		0		0
Additions charged to other accounts	0		0		0
Deductions	0		0		0
Balance at end of period	0.3		0.3		0.3
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	23.8		23.9		26.6
Additions charged to costs and expenses	0.1		0.3		0.1
Additions charged to other accounts	0		0		0
Deductions	3.2	[4]	0.4	[4]	2.8	[4]
Balance at end of period	$ 20.7		$ 23.8		$ 23.9

[1] Recoveries.

[2] Uncollectible accounts charged off.

[3] Payment of claims.

[4] Reversal of tax valuation allowance.