Investment in Unconsolidated Affiliates Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
OGE's share of Enable net income	$ 9.1	$ 20.6	$ 30.4	$ 44.4
Amortization of basis difference	3.0	3.6	5.9	7.1
Elimination of Enogex Holdings fair value and other adjustments	4.6	4.0	8.7	8.4
Equity in earnings of unconsolidated affiliates	$ 16.7	$ 28.2	$ 45.0	$ 59.9