Investment in Unconsolidated Affiliates (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended				1 Months Ended			1 Months Ended	3 Months Ended			1 Months Ended	3 Months Ended	9 Months Ended
	May 31, 2014	Apr. 30, 2014	May 01, 2013 Enogex LLC [Member]	May 13, 2014 Southeast Supply Header, LLC [Member]	Apr. 30, 2014 ArcLight group [Member]	May 01, 2013 ArcLight group [Member]	May 01, 2013 OGE Holdings [Member]	May 30, 2014 OGE Energy [Member]	Sep. 30, 2014 OGE Energy [Member]	Mar. 31, 2014 OGE Energy [Member]	Sep. 30, 2014 CenterPoint [Member]	Apr. 30, 2014 Enable Midstream Partners [Member]	Sep. 30, 2014 Enable Midstream Partners [Member]	Sep. 30, 2014 Enable Midstream Partners [Member]
Percentage of Enogex LLC Contributed			100.00%
Contributions to Pay Down Short-Term Debt						$ 107.0	$ 9.1
Percentage Share of Management Rights									50.00%		50.00%
Partners' Capital Account, Units, Sold in Public Offering					3,750,000							25,000,000
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest		6.00%						26.70%	26.30%	28.50%
Proceeds from Issuance Initial Public Offering												464.0
Percentage of Subsidiary Contributed				24.95%
Partners' Capital Account, Units, Acquisitions	6,322,457
Percent of Incentive Distribution Rights									60.00%		40.00%
Distributions from unconsolidated affiliates													$ 33.6	$ 110.1