Supplemental Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows affected by changes in:
Receivables	$ 12.5	$ (41.2)
Accounts receivable pledged as collateral	(95.0)	0
Fuel inventories	(5.4)	12.9
Materials and supplies	(7.8)	(4.8)
Accounts payable	(49.4)	(71.5)
Accrued taxes	65.4	52.5
Accrued interest	(16.6)	(6.1)
Deferred refueling outage costs	13.4	(23.8)
Fuel adjustment clauses	13.1	(27.3)
Pension and post-retirement benefit obligations	21.9	22.0
Increase (Decrease) in Allowance for Equity Funds Used During Construction	(0.3)	(0.3)
Forward starting swaps settlement	0	(26.1)
Iatan Nos. 1 and 2 impact of disallowed construction costs	0	2.3
Uncertain tax positions	(4.4)	(20.2)
Other Operating Activities, Cash Flow Statement	(14.2)	(22.7)
Total other operating activities	(66.8)	(154.3)
Cash paid during the period:
Interest Paid, Net	185.4	195.1
Income Taxes Paid	3.3	2.4
Non-cash investing activities:
Liabilities assumed for capital expenditures	52.2	34.8
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	(35.1)	(39.5)
Accounts receivable pledged as collateral	(15.0)	0
Fuel inventories	(6.2)	2.9
Materials and supplies	(6.1)	(4.3)
Accounts payable	(18.0)	(43.2)
Accrued taxes	76.5	40.3
Accrued interest	9.8	7.9
Deferred refueling outage costs	13.4	(23.8)
Fuel adjustment clauses	(0.9)	(22.0)
Pension and post-retirement benefit obligations	24.7	32.1
Iatan Nos. 1 and 2 impact of disallowed construction costs	0	1.5
Uncertain tax positions	1.2	(10.1)
Other Operating Activities, Cash Flow Statement	(20.9)	(16.1)
Total other operating activities	23.4	(74.3)
Cash paid during the period:
Interest Paid, Net	77.3	74.6
Income Taxes Paid	0	0.1
Non-cash investing activities:
Liabilities assumed for capital expenditures	$ 48.0	$ 30.7