Investment in Unconsolidated Affiliate and Related Party Transactions Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Net income	$ 485.3	$ 400.3	$ 289.5
Timing Differences Related to Equity Method Investee Net Income	0.0	0.0	(12.2)
Net Income Used to Calculate Equity in Earnings	$ 485.3	$ 400.3	$ 268.2
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest	25.60%	25.70%	25.70%
Proportionate Unconsolidated Affiliate Net Income	$ 124.4	$ 102.7	$ 70.7
OGE Energy's share of Enable net income	124.4	102.7	73.3
Amortization of basis difference	11.2	11.3	11.6
Elimination of Enable fair value step up	17.2	17.2	16.9
Equity in earnings of unconsolidated affiliates	152.8	131.2	101.8
Natural Gas Midstream Operations [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates	152.8	131.2	101.8
Preferred Partner [Member]
Schedule of Equity Method Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid	$ 0.0	0.0	(9.1)
OGE Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest	25.60%
OGE Energy [Member]
Schedule of Equity Method Investments [Line Items]
Goodwill, Impairment Loss	$ 0.0	$ 0.0	$ 2.6
Amortization of basis difference	$ 11.2