Supplemental Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Cash flows affected by changes in:
Receivables	$ 27.3	$ (14.1)
Accounts receivable pledged as collateral	(67.0)	0
Fuel inventories	(13.7)	3.2
Materials and supplies	(5.7)	(3.1)
Accounts payable	(53.7)	(67.2)
Accrued taxes	33.8	33.6
Accrued interest	(3.6)	(4.5)
Deferred refueling outage costs	9.0	(31.0)
Fuel adjustment clauses	10.5	(11.0)
Pension and post-retirement benefit obligations	13.5	7.2
Allowance for equity funds used during construction	(0.1)	(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	(0.3)	(19.6)
Other Operating Activities, Cash Flow Statement	(12.8)	(26.8)
Total other operating activities	(62.8)	(157.4)
Cash paid during the period:
Interest Paid, Net	130.5	138.4
Income Taxes Paid	3.3	0.1
Non-cash investing activities:
Liabilities assumed for capital expenditures	48.9	31.5
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	13.8	(9.7)
Accounts receivable pledged as collateral	(11.0)	0
Fuel inventories	(12.7)	(4.1)
Materials and supplies	(4.5)	(3.3)
Accounts payable	(36.5)	(47.1)
Accrued taxes	25.2	30.6
Accrued interest	(3.5)	(3.0)
Deferred refueling outage costs	9.0	(31.0)
Fuel adjustment clauses	(4.4)	(10.8)
Pension and post-retirement benefit obligations	14.9	14.1
Iatan Nos. 1 and 2 impact of disallowed construction costs	0	1.5
Uncertain tax positions	0.1	(11.8)
Other Operating Activities, Cash Flow Statement	(16.5)	(20.5)
Total other operating activities	(26.1)	(95.1)
Cash paid during the period:
Interest Paid, Net	61.3	62.2
Income Taxes Paid	0	0.1
Non-cash investing activities:
Liabilities assumed for capital expenditures	$ 44.3	$ 22.4