Supplemental Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
NON-CASH INVESTING AND FINANCING ACTIVITIES
Installment payments for Tinker electric distribution system	$ 0	$ 10.6	$ 0
Power plant long-term service agreement	9.7	0	1.7
SUPPLEMENTAL CASH FLOW INFORMATION
Interest (net of interest capitalized)	127.5	122.1	108.2
Income taxes (net of income tax refunds)	(5.5)	(1.2)	4.5
Interest costs capitalized	$ 3.4	$ 3.5	$ 10.4