Consolidated Statements of Income and Comprehensive Income (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Revenues
Electric revenues	$ 2,309.9	$ 2,318.0	$ 2,255.5
Operating Expenses
Fuel	539.5	483.8	430.7
Purchased power	94.0	203.4	213.8
Transmission of electricity by others	35.4	30.2	27.4
Utility operating and maintenance expenses	647.3	658.2	602.5
Voluntary separation program	(4.3)	12.7	0
Depreciation and amortization	272.3	273.1	331.6
General taxes	179.3	170.9	155.1
Other General and Administrative Expense	7.5	5.9	22.1
Costs and Expenses, Total	1,771.0	1,838.2	1,783.2
Operating Income (Loss)	538.9	479.8	472.3
Non-operating income	7.3	5.9	43.9
Non-operating expenses	(20.5)	(8.2)	(19.5)
Interest charges	(220.8)	(218.4)	(184.8)
Income before income tax (expense) benefit and income (loss) from equity investments	304.9	259.1	311.9
Income tax (expense) benefit	(104.6)	(84.8)	(99.0)
Loss from equity investments, net of income taxes	(0.4)	(0.1)	(1.0)
Net income	199.9	174.2	211.9
Less: Net income attributable to noncontrolling interest	0	0.2	(0.2)
Net income (loss) attributable to Great Plains Energy	199.9	174.4	211.7
Preferred stock dividend requirements	1.6	1.6	1.6
Earnings available for common shareholders	198.3	172.8	210.1
Average number of common shares outstanding (in shares)	145.5	135.6	135.1
Average number of diluted common shares outstanding	147.2	138.7	136.9
Basic earnings (loss) per common share
Basic earnings per common share	$ 1.36	$ 1.27	$ 1.55
Diluted earnings (loss) per common share
Diluted earnings per common share	$ 1.35	$ 1.25	$ 1.53
Cash dividends per common share	$ 0.855	$ 0.835	$ 0.830
Comprehensive Income
Net income	199.9	174.2	211.9
Other comprehensive income
Gain (loss) on derivative hedging instruments	(0.1)	(5.9)	(28.0)
Income tax benefit (expense)	0	2.3	10.8
Net gain (loss) on derivative hedging instruments	(0.1)	(3.6)	(17.2)
Reclassification to expenses, net of tax	12.6	10.4	6.6
Derivative hedging activity, net of tax	12.5	6.8	(10.6)
Net gain (loss) arising during period	(2.3)	(1.2)	(1.3)
Amortization of net losses included in net periodic benefit costs	0.5	0.4	0.3
Income tax benefit (expense)	0.7	0.3	0.4
Net change in unrecognized pension expense	(1.1)	(0.5)	(0.6)
Comprehensive income attributable to Great Plains Energy	211.3	180.7	200.5
Less: comprehensive income attributable to noncontrolling interest	0	0.2	(0.2)
Comprehensive income	211.3	180.5	200.7
Other comprehensive income (loss)	11.4	6.3	(11.2)
Kansas City Power and Light Company [Member]
Operating Revenues
Electric revenues	1,579.9	1,558.3	1,517.1
Operating Expenses
Fuel	384.8	333.5	278.8
Purchased power	35.5	70.8	78.9
Transmission of electricity by others	24.0	18.8	15.0
Utility operating and maintenance expenses	460.1	470.9	434.3
Voluntary separation program	(4.3)	9.2	0
Depreciation and amortization	185.6	193.1	256.4
General taxes	145.5	139.7	129.3
Other General and Administrative Expense	0	1.1	13.0
Costs and Expenses, Total	1,231.2	1,237.1	1,205.7
Operating Income (Loss)	348.7	321.2	311.4
Non-operating income	4.4	2.9	24.7
Non-operating expenses	(8.6)	(3.9)	(5.6)
Interest charges	(127.6)	(115.6)	(85.7)
Income before income tax (expense) benefit and income (loss) from equity investments	216.9	204.6	244.8
Income tax (expense) benefit	(75.3)	(69.1)	(81.6)
Net income	141.6	135.5	163.2
Comprehensive Income
Net income	141.6	135.5	163.2
Other comprehensive income
Gain (loss) on derivative hedging instruments	(0.1)	(0.6)	(0.9)
Income tax benefit (expense)	0	0.2	0.3
Net gain (loss) on derivative hedging instruments	(0.1)	(0.4)	(0.6)
Reclassification to expenses, net of tax	5.7	5.4	5.7
Derivative hedging activity, net of tax	5.6	5.0	5.1
Comprehensive income	147.2	140.5	168.3
Other comprehensive income (loss)	$ 5.6	$ 5.0	$ 5.1