Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Utility Plant, at Original Cost
Nuclear fuel, amortization	$ 175.7	$ 187.5
Common shareholder's equity
Common stock - shares authorized (in shares)	250,000,000	250,000,000
Common stock-shares issued (in shares)	154,422,890	154,254,037
Treasury stock- shares (in shares)	96,463	91,281
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%
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%
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%
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	$ 175.7	$ 187.5
Common shareholder's equity
Common stock - shares authorized (in shares)	1,000.0	1,000.0
Common stock-shares issued (in shares)	1.0	1.0