Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Current Assets
Cash and cash equivalents	$ 9.3		$ 6.2
Funds on deposit	1.0		1.4
Receivables, net	154.5		231.2
Accounts receivable pledged as collateral	174.0		95.0
Fuel inventories, at average cost	95.1		89.0
Materials and supplies, at average cost	151.3		140.3
Deferred refueling outage costs	11.9		27.5
Refundable income taxes	9.5		0.3
Deferred income taxes	88.5		7.5
Derivative instruments	1.0		1.0
Prepaid expenses and other assets	27.6		19.7
Assets, Current, Total	723.7		619.1
Utility Plant, at Original Cost
Electric	11,160.5	[1]	10,924.8	[1]
Less-accumulated depreciation	4,424.2		4,235.8
Net utility plant in service	6,736.3		6,689.0
Construction work in progress	584.5		287.9
Nuclear Fuel, Net of Amortization	81.3		76.6
Public Utilities, Property, Plant and Equipment, Net	7,402.1		7,053.5
Investments and Other Assets
Nuclear decommissioning trust fund	154.7		135.3
Regulatory Assets	1,120.9		1,058.2
Goodwill	169.0		169.0
Derivative instruments	5.5		6.8
Other Assets, Noncurrent	71.4		76.1
Investments and Other Assets, Total	1,521.5		1,445.4
Assets, Total	9,647.3		9,118.0
Current Liabilities
Notes payable	12.0		22.0
Collateralized note payable	174.0		95.0
Commercial paper	530.1		267.0
Current maturities of long-term debt	263.1		801.4
Accounts payable	330.2		275.6
Accrued taxes	27.1		25.8
Accrued interest	41.5		76.9
Accrued compensation and benefits	44.8		40.8
Pension and post-retirement liability	2.8		4.4
Other Liabilities, Current	23.9		26.0
Liabilities, Current, Total	1,449.5		1,634.9
Deferred Credits and Other Liabilities
Deferred income taxes	832.4		628.6
Deferred tax credits	128.8		131.2
Asset retirement obligations	149.3		149.6
Pension and post-retirement liability	557.5		461.9
Regulatory Liabilities	283.8		268.5
Other Liabilities, Noncurrent	110.2		101.1
Liabilities, Noncurrent, Total	2,062.0		1,740.9
Common shareholders' equity
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 loss	(38.4)		(49.8)
Common Shareholders' Equity, Total	3,340.0		2,959.9
Noncontrolling interest	0		1.0
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	39.0		39.0
Long-term debt	2,756.8	[2]	2,742.3	[2]
Total Capitalization	6,135.8		5,742.2
Commitments and Contingencies
Liabilities and Equity, Total	9,647.3		9,118.0
Cumulative Preferred Stock [Member] | Preferred Stock 3 Point 80 [Member]
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	10.0		10.0
Cumulative Preferred Stock [Member] | Preferred Stock 4 Point 50 [Member]
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	10.0		10.0
Cumulative Preferred Stock [Member] | Preferred Stock 4 Point 20 [Member]
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	7.0		7.0
Cumulative Preferred Stock [Member] | Preferred Stock 4 Point 35 [Member]
Cumulative preferred stock $100 par value
Preferred Stock, Value, Issued	12.0		12.0
Kansas City Power and Light Company [Member]
Current Assets
Cash and cash equivalents	5.2		1.9
Funds on deposit	0.1		0.1
Receivables, net	163.2		172.9
Accounts receivable pledged as collateral	110.0		95.0
Fuel inventories, at average cost	63.6		59.0
Materials and supplies, at average cost	110.1		101.1
Deferred refueling outage costs	11.9		27.5
Refundable income taxes	9.1		5.7
Deferred income taxes	4.6		0
Prepaid expenses and other assets	23.8		16.0
Assets, Current, Total	501.6		479.2
Utility Plant, at Original Cost
Electric	7,971.4	[3]	7,829.3	[3]
Less-accumulated depreciation	3,374.4		3,243.0
Net utility plant in service	4,597.0		4,586.3
Construction work in progress	486.5		203.5
Nuclear Fuel, Net of Amortization	81.3		76.6
Public Utilities, Property, Plant and Equipment, Net	5,164.8		4,866.4
Investments and Other Assets
Nuclear decommissioning trust fund	154.7		135.3
Regulatory Assets	853.2		780.7
Other Assets, Noncurrent	29.5		30.6
Investments and Other Assets, Total	1,037.4		946.6
Assets, Total	6,703.8		6,292.2
Current Liabilities
Notes payable	0		0
Collateralized note payable	110.0		95.0
Commercial paper	361.0		227.0
Current maturities of long-term debt	0.4		12.7
Accounts payable	254.0		214.8
Accrued taxes	21.9		20.6
Accrued interest	27.7		30.0
Accrued compensation and benefits	44.8		40.8
Pension and post-retirement liability	1.4		3.0
Other Liabilities, Current	12.8		13.7
Liabilities, Current, Total	834.0		657.6
Deferred Credits and Other Liabilities
Deferred income taxes	836.4		772.7
Deferred tax credits	126.1		127.9
Asset retirement obligations	133.2		134.3
Pension and post-retirement liability	534.5		440.9
Regulatory Liabilities	153.0		142.8
Other Liabilities, Noncurrent	88.2		68.6
Liabilities, Noncurrent, Total	1,871.4		1,687.2
Common shareholders' equity
Common Stock, Value, Issued	1,563.1		1,563.1
Retained earnings	559.4		513.8
Accumulated other comprehensive loss	(25.8)		(31.4)
Common Shareholders' Equity, Total	2,096.7		2,045.5
Cumulative preferred stock $100 par value
Long-term debt	1,901.7	[2]	1,901.9	[2]
Total Capitalization	3,998.4		3,947.4
Commitments and Contingencies
Liabilities and Equity, Total	$ 6,703.8		$ 6,292.2

[1] (a) Includes $104.5 million and $105.5 million at December 31, 2012 and 2011, respectively, of land and other assets that are not depreciated.

[2] 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

[3] (a) Includes $54.7 million and $59.8 million at December 31, 2012 and 2011, respectively, of land and other assets that are not depreciated.