Transactions with Affiliates (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2017 USD ($)	Jun. 30, 2017 USD ($) employee	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) employee	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Related Party Transaction [Line Items]
Advances to affiliate		$ 123,999		$ 123,999		$ 45,137
Related party transaction, rate				0.83%
Entity number of employees | employee		0		0
Related party transaction, expenses from transactions with related party		$ 23,200	$ 21,100	$ 46,200	$ 46,100
Severance and other related costs					2,000
Cash distributions to parent				107,000	$ 86,000
Williams Partners L.P. [Member]
Related Party Transaction [Line Items]
Advances to affiliate		$ 124,000		$ 124,000		$ 45,100
Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent	$ 41,000