Investment in Unconsolidated Affiliate and Related Party Transactions (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Apr. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	May. 13, 2014	May. 01, 2013
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		$ 775.5
Enable Midstream Partners [Member]
Schedule of Equity Method Investments [Line Items]
Partners' Capital Account, Units, Sold in Public Offering	25,000,000
Distributions received		$ 35.3	$ 34.3
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
Southeast Supply Header, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of Subsidiary Contributed				24.95%
OGE Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Limited Partner Units Owned		111,000,000
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest		26.30%
Subordinated Units Held by Limited Partners of the LLC or LP		68,200,000
Percent of Incentive Distribution Rights		60.00%
CenterPoint [Member]
Schedule of Equity Method Investments [Line Items]
Percent of Incentive Distribution Rights		40.00%