Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current Assets
Cash and cash equivalents	$ 6.2	$ 10.8
Funds on deposit	1.4	5.2
Receivables, net	231.2	241.7
Accounts receivable pledged as collateral	95.0	95.0
Fuel inventories, at average cost	89.0	85.1
Materials and supplies, at average cost	140.3	132.8
Deferred refueling outage costs	27.5	9.6
Refundable income taxes	0.3	2.1
Deferred income taxes	7.5	14.3
Derivative instruments	1.0	1.1
Prepaid expenses and other assets	19.7	13.9
Total	619.1	611.6
Utility Plant, at Original Cost
Electric	10,924.8	10,536.9
Less-accumulated depreciation	4,235.8	4,031.3
Net utility plant in service	6,689.0	6,505.6
Construction work in progress	287.9	307.5
Nuclear fuel, net of amortization of $132.7 and $131.1	76.6	79.2
Total	7,053.5	6,892.3
Investments and Other Assets
Nuclear decommissioning trust fund	135.3	129.2
Regulatory Assets	1,058.2	924.0
Goodwill	169.0	169.0
Derivative instruments	6.8	7.8
Other	76.1	84.3
Total	1,445.4	1,314.3
Total	9,118.0	8,818.2
Current Liabilities
Notes payable	22.0	9.5
Collateralized note payable	95.0	95.0
Commercial paper	267.0	263.5
Current maturities of long-term debt	801.4	485.7
Accounts payable	275.6	276.3
Accrued taxes	25.8	26.6
Accrued interest	76.9	75.4
Accrued compensation and benefits	40.8	46.8
Pension and post-retirement liability	4.4	4.1
Derivative instruments	0	20.8
Other	26.0	35.6
Total	1,634.9	1,339.3
Deferred Credits and Other Liabilities
Deferred income taxes	628.6	518.3
Deferred tax credits	131.2	133.4
Asset retirement obligations	149.6	143.3
Pension and post-retirement liability	461.9	427.5
Regulatory Liabilities	268.5	258.2
Other	101.1	129.4
Total	1,740.9	1,610.1
Common shareholders' equity
Common stock - Great Plains - 250,000,000 shares authorized without par value 136,406,306 and 136,113,954 shares issued, stated value; Kansas City Power and Light Company - 1,000 shares authorized without par value, 1 share issued, stated value	2,330.6	2,324.4
Retained earnings	684.7	626.5
Treasury stock-264,567 and 400,889 shares, at cost	(5.6)	(8.9)
Accumulated other comprehensive loss	(49.8)	(56.1)
Total	2,959.9	2,885.9
Noncontrolling interest	1.0	1.2
Cumulative preferred stock $100 par value
3.8% - 100,000 shares issued	10.0	10.0
4.50% - 100,000 shares issued	10.0	10.0
4.20% - 70,000 shares issued	7.0	7.0
4.35% - 120,000 shares issued	12.0	12.0
Total	39.0	39.0
Long-term debt (Note 11)	2,742.3	2,942.7
Total	5,742.2	5,868.8
Commitments and Contingencies (Note 14)
Total	9,118.0	8,818.2
Kansas City Power and Light Company [Member]
Current Assets
Cash and cash equivalents	1.9	3.6
Funds on deposit	0.1	0.4
Receivables, net	172.9	169.4
Accounts receivable pledged as collateral	95.0	95.0
Fuel inventories, at average cost	59.0	44.9
Materials and supplies, at average cost	101.1	94.4
Deferred refueling outage costs	27.5	9.6
Refundable income taxes	5.7	9.0
Deferred income taxes	0	5.6
Prepaid expenses and other assets	16.0	10.0
Total	479.2	441.9
Utility Plant, at Original Cost
Electric	7,829.3	7,540.9
Less-accumulated depreciation	3,243.0	3,104.4
Net utility plant in service	4,586.3	4,436.5
Construction work in progress	203.5	227.6
Nuclear fuel, net of amortization of $132.7 and $131.1	76.6	79.2
Total	4,866.4	4,743.3
Investments and Other Assets
Nuclear decommissioning trust fund	135.3	129.2
Regulatory Assets	780.7	679.6
Other	30.6	32.3
Total	946.6	841.1
Total	6,292.2	6,026.3
Current Liabilities
Notes payable	0	0
Collateralized note payable	95.0	95.0
Commercial paper	227.0	263.5
Current maturities of long-term debt	12.7	150.3
Accounts payable	214.8	201.7
Accrued taxes	20.6	21.3
Accrued interest	30.0	26.2
Accrued compensation and benefits	40.8	46.8
Pension and post-retirement liability	3.0	2.6
Other	13.7	7.8
Total	657.6	815.2
Deferred Credits and Other Liabilities
Deferred income taxes	772.7	692.0
Deferred tax credits	127.9	129.4
Asset retirement obligations	134.3	129.7
Pension and post-retirement liability	440.9	407.3
Regulatory Liabilities	142.8	141.3
Other	68.6	76.7
Total	1,687.2	1,576.4
Common shareholders' equity
Common stock - Great Plains - 250,000,000 shares authorized without par value 136,406,306 and 136,113,954 shares issued, stated value; Kansas City Power and Light Company - 1,000 shares authorized without par value, 1 share issued, stated value	1,563.1	1,563.1
Retained earnings	513.8	478.3
Accumulated other comprehensive loss	(31.4)	(36.4)
Total	2,045.5	2,005.0
Cumulative preferred stock $100 par value
Long-term debt (Note 11)	1,901.9	1,629.7
Total	3,947.4	3,634.7
Total	$ 6,292.2	$ 6,026.3