Transactions with Major Customers and Affiliates (Details) $ in Thousands		1 Months Ended		12 Months Ended
	Dec. 31, 2019 USD ($) employee	Jan. 31, 2020 USD ($)	Jul. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) employee	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Nov. 01, 2019 USD ($)
Related Party Transaction [Line Items]
Advances from affiliate	$ 252,549			$ 252,549	$ 0
Advances to affiliate	$ 0			$ 0	33,034
Related party transaction, rate				1.49%
Entity number of employees | employee	0			0
Expenses, related party				$ 412,400	395,300	$ 370,400
Severance Costs				28,800
Cash distributions to parent				(824,000)	(490,000)	(430,000)
Cash contributions from parent				0	340,000	410,000
Non-cash distribution of investments in subsidiaries	$ 36,600
Duration Of Period For Deferred Revenue Recognition			25 years
Hillabee Expansion Project [Member]
Related Party Transaction [Line Items]
Deferred Revenue, Additions			$ 240,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Operating revenues, related party				10,500	10,100	10,300
Cost of natural gas sales, related party				4,000	5,400	3,900
Expenses, related party				(4,400)	(4,700)	(3,700)
Williams Companies Inc [Member]
Related Party Transaction [Line Items]
Advances from affiliate	$ 252,500			252,500
Advances to affiliate					33,000
Cash distributions to parent				824,000	490,000	430,000
Williams Companies Inc [Member] | Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent		$ 270,000
Atlantic Sunrise Project [Member]
Related Party Transaction [Line Items]
Additions to other financing obligations							$ 25,000
Dominion Energy, Inc.
Revenue, Major Customer [Line Items]
Operating revenues				250,700	113,500	72,000
Duke Energy Corporation
Revenue, Major Customer [Line Items]
Operating revenues				222,500	194,500	198,400
The Southern Company, Inc.
Revenue, Major Customer [Line Items]
Operating revenues				$ 216,100	$ 166,200	$ 160,000