Summary of Significant Accounting Policies Asset Retirement Obligation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1	$ 54.0	$ 24.8
Liabilities settled	(0.1)	0
Accretion expense	0.6	0.4
Revisions in estimated cash flows	0	26.7	[1]
Balance at March 31	$ 54.5	$ 51.9

[1] Due to changes to OG&E's asset retirement obligations related to its wind farms due to a change in the assumption related to the timing of removal used in the valuation of the asset retirement obligations.