Summary of Significant Accounting Policies Asset Retirement Obligation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1	$ 24.8		$ 11.1
Liabilities incurred	0.4	[1]	13.0	[1]
Accretion expense	1.9		0.7
Revisions in estimated cash flows	26.9	[2]	0
Balance at December 31	$ 54.0		$ 24.8

[1] Due to certain Enogex compression assets in 2012 and OG&E's Crossroads wind farm in 2011.

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