Supplemental Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows affected by changes in:
Receivables	$ (7.1)	$ 76.8	$ 3.6
Accounts receivable pledged as collateral	(1.0)	(79.0)	0
Fuel inventories	18.7	(6.1)	(3.9)
Materials and supplies	(1.0)	(11.0)	(7.5)
Accounts payable	26.4	57.3	5.7
Accrued taxes	2.2	(7.8)	1.4
Accrued interest	3.9	(35.2)	1.5
Deferred refueling outage costs	(17.6)	15.6	(17.9)
Pension and post-retirement benefit obligations	31.3	14.4	(56.0)
Allowance for equity funds used during construction	(14.1)	(1.3)	(1.0)
Interest rate hedge settlement	0	0	(26.1)
Fuel recovery mechanism	(1.3)	22.5	(1.7)
Uncertain tax positions	(0.8)	(4.7)	(20.8)
Other operating activities	(15.5)	(29.8)	(24.8)
Total other operating activities	24.1	11.7	(147.5)
Cash paid during the period:
Interest Paid, Net	170.8	247.9	254.4
Income Taxes Paid	0	3.3	2.8
Non-cash investing activities:
Liabilities accrued for capital expenditures	48.1	57.5	39.7
Kansas City Power and Light Company [Member]
Cash flows affected by changes in:
Receivables	(12.6)	8.8	(20.2)
Accounts receivable pledged as collateral	0	(15.0)	0
Fuel inventories	13.3	(4.6)	(14.1)
Materials and supplies	1.1	(9.0)	(6.7)
Accounts payable	7.3	48.3	11.0
Accrued taxes	(3.7)	(2.0)	2.7
Accrued interest	1.4	(2.3)	3.8
Deferred refueling outage costs	(17.6)	15.6	(17.9)
Pension and post-retirement benefit obligations	35.7	18.0	(45.6)
Allowance for equity funds used during construction	(14.1)	(1.3)	(0.7)
Fuel recovery mechanism	(1.8)	5.1	(5.8)
Uncertain tax positions	(10.5)	1.8	(10.4)
Other operating activities	(7.7)	(35.5)	(14.4)
Total other operating activities	(9.2)	27.9	(118.3)
Cash paid during the period:
Interest Paid, Net	111.7	118.0	111.3
Income Taxes Paid	4.6	18.0	0.1
Non-cash investing activities:
Liabilities accrued for capital expenditures	$ 40.5	$ 48.4	$ 32.0