Investment in Unconsolidated Affiliates Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
OGE's share of Enable Net Income	$ 20.6	$ 32.2	$ 44.4	$ 74.7
Amortization of basis difference	3.6	3.4	7.1	7.0
Elimination of Enogex Holdings fair value and other adjustments	4.0	3.7	8.4	5.5
OGE's Equity in earnings of unconsolidated affiliates	$ 28.2	$ 39.3	$ 59.9	$ 87.2