Investments in Unconsolidated Affiliates (Details) - USD ($)		2 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Oct. 31, 2016
Schedule of Equity Method Investments [Line Items]
Investments in equity method unconsolidated affiliates		$ 212,200,000		$ 199,200,000
Equity in earnings of unconsolidated affiliates		2,300,000	$ 4,600,000
Accounts payable to affiliated companies	[1],[2]	10,500,000		8,700,000
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Related party expenses		4,700,000	4,900,000
Accounts payable to affiliated companies		$ 2,400,000		2,400,000
Cardinal Pipeline Company
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		21.49%
Investments in equity method unconsolidated affiliates		$ 13,900,000		14,200,000
Cardinal Pipeline Company | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Related party expenses		1,500,000	1,500,000
Accounts payable to affiliated companies		$ 700,000		700,000
Pine Needle Company
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		45.00%
Investments in equity method unconsolidated affiliates		$ 16,300,000		16,600,000
Pine Needle Company | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Related party expenses		1,700,000	1,900,000
Accounts payable to affiliated companies		$ 900,000		900,000
Hardy Storage
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		50.00%
Investments in equity method unconsolidated affiliates		$ 43,400,000		42,100,000
Hardy Storage | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Related party expenses		1,500,000	$ 1,500,000
Accounts payable to affiliated companies		$ 800,000		800,000
Constitution Pipeline Company
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		24.00%
Investments in equity method unconsolidated affiliates		$ 92,400,000		93,100,000
Target Pipeline In Service Date		2018
Estimated Contributions For Pipeline And Construction Costs		$ 229,300,000
Capital contributions to or payments to acquire equity method investments		200,000
Total Contributions To Equity Method Investments For Project		85,000,000
Equity Method Investment, Summarized Financial Information [Abstract]
Equity Method Investment, Other than Temporary Impairment		$ 0
Atlantic Coast Pipeline
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		7.00%
Investments in equity method unconsolidated affiliates		$ 46,200,000		$ 33,200,000
Target Pipeline In Service Date		2019
Capital contributions to or payments to acquire equity method investments		$ 12,100,000
Total Contributions To Equity Method Investments For Project		58,100,000
Maximum Funding Obligation Under Equity Contribution Agreements		10,600,000
Atlantic Coast Pipeline | Minimum
Schedule of Equity Method Investments [Line Items]
Estimated Contributions For Pipeline And Construction Costs		350,000,000
Atlantic Coast Pipeline | Maximum
Schedule of Equity Method Investments [Line Items]
Estimated Contributions For Pipeline And Construction Costs		$ 385,000,000

[1] See Note 11 for amounts attributable to investments in unconsolidated affiliates.

[2] See Note 9 for details on related party transactions with Duke Energy.