Investment in Unconsolidated Affiliates Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Net income	$ 110.8	$ 86.0
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	736.6		$ 743.7
Timing Differences Related to Equity Method Investee Net Income	0.0	(11.7)
Net Income Used to Calculate Equity in Earnings	110.8	74.3
Proportionate Unconsolidated Affiliate Net Income	28.5	19.5
OGE Energy's share of Enable net income	28.5	21.3
Amortization of basis difference	2.8	2.9
Elimination of Enable fair value step up	4.3	4.1
Equity in earnings of unconsolidated affiliates	$ 35.6	$ 28.3
OGE Holdings [Member]
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest	25.70%	26.30%
OGE Energy [Member]
Reconciliation of Equity in Earnings of Unconsolidated Affiliates [Line Items]
Goodwill, Impairment Loss	$ 0.0	$ (1.8)