Investment in Unconsolidated Affiliate and Related Party Transactions Reconciliation of Equity in Earnings of Unconsolidated Affiliates (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Net income (loss)		$ 289.5	$ (752.0)		$ 530.0
Timing Differences Related to Equity Method Investee Net Income		(12.1)	12.1
Net Income Used to Calculate Equity in Earnings		268.3	(739.9)
Proportionate Unconsolidated Affiliate Net Income		70.7	(194.4)
OGE Energy's share of Enable net income (loss)		73.3	(16.0)
Amortization of basis difference		11.6	13.5
Elimination of Enable fair value step up		16.9	18.0
Equity in earnings of unconsolidated affiliates		101.8	15.5	[1]	172.6
Natural Gas Midstream Operations [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates		101.8	15.5	[1]	$ 172.6
Preferred Partner [Member]
Schedule of Equity Method Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid		9.1	0.0
OGE Energy [Member]
Schedule of Equity Method Investments [Line Items]
Goodwill, Impairment Loss	$ (108.4)	$ 2.6	$ 178.4

[1] In 2015, The Company recorded a $108.4 million pre-tax charge during the third quarter of 2015 for its share of the goodwill impairment, as adjusted for the basis difference. See Note 3 for further discussion of Enable's goodwill impairment.