Summary of Significant Accounting Policies Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Capital contribution from OGE Energy			$ 0	$ 50.0
Dividends declared on common stock			(75.0)
Operating Costs Charged [Member] | Og and E [Member]
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party	28.8	31.4	89.0	95.8
Og and E [Member] | Natural Gas Transportation [Member] | Enogex [Member]
Related Party Transaction, Expenses from Transactions with Related Party	8.7	8.7	26.1	26.1
Og and E [Member] | Natural Gas Purchases [Member] | Enogex [Member]
Related Party Transaction, Purchases from Related Party	8.7	10.0	18.3	31.4
Related Party Transaction, Due from (to) Related Party	0.3		0.3		1.7
Og and E [Member] | Natural Gas Storage [Member] | Enogex [Member]
Related Party Transaction, Expenses from Transactions with Related Party	3.2	3.2	9.6	9.6
Physical [Member] | Derivative Purchases [Member] | Designated as Hedging Instrument [Member] | Natural Gas [Member]
Derivative, Nonmonetary Notional Amount	50,000		50,000
Retained Earnings
Capital contribution from OGE Energy				0
Dividends declared on common stock			$ (75.0)	$ 0