Summary of Significant Accounting Policies Asset Retirement Obligation (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Current Fiscal Year End Date		--12-31
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1		$ 58.6	$ 55.2
Accretion expense		2.6	2.5
Revisions in estimated cash flows	[1]	1.6	1.7
Additions	[2]	0.9	0.0
Liabilities settled	[3]	(0.4)	(0.8)
Balance at December 31		$ 63.3	$ 58.6

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

[2] OG&E recorded an asset retirement obligation for $0.9 million for the ash pond located at the Muskogee generating facility.

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