Summary of Significant Accounting Policies Asset Retirement Obligation (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1	$ 55.2		$ 54.0
Liabilities settled	(0.2)		(0.4)
Accretion expense	1.9		1.7
Revisions in estimated cash flows	1.7	[1]	(0.7)	[1]
Balance at September 30	$ 58.6		$ 54.6

[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.