Investment in Unconsolidated Affiliates Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Net income	$ 86.2	$ 34.7	$ 197.4	$ 120.7
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	729.4		729.4		$ 743.7
Timing Differences Related to Equity Method Investee Net Income	0.0	1.5	0.0	(10.2)
Net Income Used to Calculate Equity in Earnings	86.2	36.2	197.4	110.5
Proportionate Unconsolidated Affiliate Net Income	22.2	9.1	50.7	28.6
OGE Energy's share of Enable net income	22.2	9.1	50.7	30.4
Amortization of basis difference	2.9	3.0	5.7	5.9
Elimination of Enable fair value step up	4.3	4.6	8.6	8.7
Equity in earnings of unconsolidated affiliates	$ 29.4	$ 16.7	$ 65.0	$ 45.0
OGE Holdings [Member]
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest	25.70%	26.30%	25.70%	26.30%
OGE Energy [Member]
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Goodwill, Impairment Loss	$ 0.0	$ 0.0	$ 0.0	$ (1.8)