Summary of Significant Accounting Policies Asset Retirement Obligation (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015		Jun. 30, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1	$ 58.6		$ 55.2
Liabilities settled (A)	(0.5)	[1]	0.0
Accretion expense	1.3		1.3
Balance at June 30	$ 59.4		$ 56.5

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