Investment in Unconsolidated Affiliate and Related Party Transactions (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 01, 2013
Schedule of Equity Method Investments [Line Items]
Limited Partner Units Owned	111.0
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest	25.60%	25.70%	25.70%
Distribution Made to Limited Partner, Distributions Declared, Per Unit	$ 0.31800
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 680.3	$ 714.2
Equity in earnings of unconsolidated affiliates	152.8	131.2	$ 101.8
Enable Midstream Partners [Member]
Schedule of Equity Method Investments [Line Items]
Distributions received	$ 141.2	141.2	141.2
Enogex LLC [Member]
Schedule of Equity Method Investments [Line Items]
Increase in fair value of net assets				$ 2,200.0
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)
Percentage Share of Management Rights	50.00%
CenterPoint [Member]
Schedule of Equity Method Investments [Line Items]
Percentage Share of Management Rights	50.00%
Natural Gas Midstream Operations [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates	$ 152.8	$ 131.2	$ 101.8