Schedule I Financial Statements of Parent Company Schedule I Financial Statements of Parent Company Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Current Assets
Taxes receivable	$ 9.5		$ 0.3
Assets, Current, Total	723.7		619.1
Investments and Other Assets
Deferred income taxes	(832.4)		(628.6)
Other investments and other assets	71.4		76.1
Assets, Total	9,647.3		9,118.0		8,818.2
Current Liabilities
Notes payable	12.0		22.0
Current maturities of long-term debt	263.1		801.4
Accrued taxes	27.1		25.8
Accrued interest	41.5		76.9
Other current liabilities	23.9		26.0
Liabilities, Current, Total	1,449.5		1,634.9
Deferred Credits and Other Liabilities
Liabilities, Noncurrent, Total	2,062.0		1,740.9
Capitalization
Common Stock, Value, Issued	2,624.7		2,330.6
Retained earnings	758.8		684.7
Treasury Stock, Value	(5.1)		(5.6)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(38.4)		(49.8)
Common Shareholders' Equity, Total	3,340.0		2,959.9		2,885.9
Preferred Stock, Value, Issued	39.0		39.0
Long-term debt	2,756.8	[1]	2,742.3	[1]
Total Capitalization	6,135.8		5,742.2
Commitments and Contingencies
Liabilities and Equity, Total	9,647.3		9,118.0
Parent Company [Member]
Current Assets
Accounts receivable from subsidiaries	0.1		0
Notes receivable from subsidiaries, current	0.6		0.6
Money pool receivable	4.0		0.9
Taxes receivable	0		0.9
Other current assets	2.4		0.6
Assets, Current, Total	7.1		3.0
Investments and Other Assets
Investment in KCP&L	2,096.7		2,045.5
Investment in other subsidiaries	1,405.4		1,377.0
Notes receivable from subsidiaries, noncurrent	883.6		596.2
Deferred income taxes	32.3		33.7
Other investments and other assets	7.6		6.4
Total investments and other assets	4,425.6		4,058.8
Assets, Total	4,432.7		4,061.8
Current Liabilities
Notes payable	12.0		22.0
Current maturities of long-term debt	250.0		287.5
Accounts payable to subsidiaries	34.1		31.8
Accrued taxes	0.5		5.1
Accrued interest	6.8		7.6
Other current liabilities	2.1		2.9
Liabilities, Current, Total	305.5		356.9
Deferred Credits and Other Liabilities
Liabilities, Noncurrent, Total	5.2		6.7
Capitalization
Common Stock, Value, Issued	2,624.7		2,330.6
Retained earnings	758.8		684.7
Treasury Stock, Value	(5.1)		(5.6)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(38.4)		(49.8)
Common Shareholders' Equity, Total	3,340.0		2,959.9
Preferred Stock, Value, Issued	39.0		39.0
Long-term debt	743.0		699.3
Total Capitalization	4,122.0		3,698.2
Commitments and Contingencies
Liabilities and Equity, Total	4,432.7		4,061.8
Preferred Stock 3 Point 80 [Member] | Parent Company [Member]
Capitalization
Preferred Stock, Value, Issued	10.0		10.0
Preferred Stock 4 Point 50 [Member] | Parent Company [Member]
Capitalization
Preferred Stock, Value, Issued	10.0		10.0
Preferred Stock 4 Point 20 [Member] | Parent Company [Member]
Capitalization
Preferred Stock, Value, Issued	7.0		7.0
Preferred Stock 4 Point 35 [Member] | Parent Company [Member]
Capitalization
Preferred Stock, Value, Issued	$ 12.0		$ 12.0

[1] Does not include $39.5 million EIRR Series 1993B, $63.3 million EIRR Series 2007 A-1 and $10.0 million EIRR Series 2007 A-2 bonds because the bonds have been repurchased and are held by KCP&L