Transactions with Affiliates (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 30, 2015 USD ($)	Jun. 30, 2015 USD ($) employee	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) employee	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Related Party Transaction [Line Items]
Advances to affiliate		$ 161,147		$ 161,147		$ 135,054
Related party transaction, rate				0.01%
Entity number of employees | employee		0		0
Related party transaction, expenses from transactions with related party		$ 24,900	$ 25,000	$ 50,200	$ 50,400
Cash distributions to parent				88,000	$ 104,000
Williams Partners L.P. [Member]
Related Party Transaction [Line Items]
Advances to affiliate		$ 161,100		$ 161,100		$ 135,100
Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent	$ 41,000