Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 147.3	$ 157.4
Common shareholder's equity
Common stock - shares authorized (in shares)	250,000,000	250,000,000
Common stock-shares issued (in shares)	153,894,724	153,779,806
Treasury stock- shares (in shares)	121,246	250,236
Cumulative Preferred Stock [Member] | Preferred Stock 3 Point 80 [Member]
Cumulative preferred stock
Cumulative preferred stock par value (in dollars per share)	$ 100.00	$ 100.00
Cumulative preferred stock, Shares issued (in share)	100,000	100,000
Preferred Stock, Dividend Rate, Percentage	3.80%	3.80%
Cumulative Preferred Stock [Member] | Preferred Stock 4 Point 50 [Member]
Cumulative preferred stock
Cumulative preferred stock par value (in dollars per share)	$ 100.00	$ 100.00
Cumulative preferred stock, Shares issued (in share)	100,000	100,000
Preferred Stock, Dividend Rate, Percentage	4.50%	4.50%
Cumulative Preferred Stock [Member] | Preferred Stock 4 Point 20 [Member]
Cumulative preferred stock
Cumulative preferred stock par value (in dollars per share)	$ 100.00	$ 100.00
Cumulative preferred stock, Shares issued (in share)	70,000	70,000
Preferred Stock, Dividend Rate, Percentage	4.20%	4.20%
Cumulative Preferred Stock [Member] | Preferred Stock 4 Point 35 [Member]
Cumulative preferred stock
Cumulative preferred stock par value (in dollars per share)	$ 100.00	$ 100.00
Cumulative preferred stock, Shares issued (in share)	120,000	120,000
Preferred Stock, Dividend Rate, Percentage	4.35%	4.35%
Kansas City Power and Light Company [Member]
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 147.3	$ 157.4
Common shareholder's equity
Common stock - shares authorized (in shares)	1,000	1,000
Common stock-shares issued (in shares)	1	1