Investment in Unconsolidated Affiliate and Related Party Transactions (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Apr. 30, 2014	Dec. 31, 2016	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014	May 01, 2013
Schedule of Equity Method Investments [Line Items]
Accounts receivable - unconsolidated affiliates		$ 2.5		$ 2.5	$ 1.7
Limited Partner Units Owned		111.0		111.0
Distribution Made to Limited Partner, Distributions Declared, Per Unit		$ 0.31800
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		$ 743.7		$ 743.7	783.5
Equity in earnings of unconsolidated affiliates				101.8	15.5	[1]	$ 172.6
Enable Midstream Partners [Member]
Schedule of Equity Method Investments [Line Items]
Goodwill, Impairment Loss			$ 1,086.4
Partners' Capital Account, Units, Sold in Public Offering	25.0
Distributions received				$ 141.2	$ 139.3		143.7
Enogex LLC [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of Enogex LLC Contributed								100.00%
Increase in fair value of net assets								$ 2,200.0
OGE Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest				25.70%	26.30%
Subordinated Units Held by Limited Partners of the LLC or LP				68.2
OGE Energy [Member]
Schedule of Equity Method Investments [Line Items]
Goodwill, Impairment Loss			$ 108.4	$ (2.6)	$ (178.4)
Percentage Share of Management Rights		50.00%		50.00%
CenterPoint [Member]
Schedule of Equity Method Investments [Line Items]
Percentage Share of Management Rights		50.00%		50.00%
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

[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.