Summary of Significant Accounting Policies Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1	$ 53.6	$ 24.8
Accretion expense	1.7	1.5
Revisions in estimated cash flows	(0.7)	26.7	[1]
Balance at September 30	$ 54.6	$ 53.0

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