Summary of Significant Accounting Policies Asset Retirement Obligation (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1		$ 58.6	$ 55.2
Liabilities settled	[1]	(0.4)	(0.2)
Accretion expense		1.9	1.9
Revisions in estimated cash flows	[2]	1.6	1.7
Balance at September 30		$ 61.7	$ 58.6

[1] In 2015, asset retirement obligations were settled for the asbestos abatement at one of OG&E's generating facilities.

[2] Assumptions changed related to the estimated cost of removal for one of OG&E's generating facilities.