Transactions with Affiliates (Details) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Oct. 31, 2017 USD ($)	Jul. 31, 2017 USD ($)	Sep. 30, 2017 USD ($) employee	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) employee	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Related Party Transaction [Line Items]
Advances to affiliate			$ 299,059		$ 299,059		$ 811,693
Related party transaction, rate					0.91%
Entity number of employees | employee			0		0
Expenses, related party			$ 91,400	$ 78,400	$ 261,100	$ 234,700
Severance Costs						6,300
Cash distributions to parent					330,000	350,000
Cash contributions from parent					110,000	372,000
Noncash distribution to Parent		$ 240,000
Duration Of Period For Deferred Revenue Recognition		25 years
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Operating revenues, related party			2,500	4,800	8,900	8,900
Cost of natural gas sales, related party			1,000	1,800	2,900	3,300
Expenses, related party			(900)	$ (1,000)	(2,700)	$ (3,400)
Williams Partners L.P. [Member]
Related Party Transaction [Line Items]
Advances to affiliate			$ 299,100		$ 299,100		$ 811,700
Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent	$ 100,000