Transactions with Major Customers and Affiliates (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) employee	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Related Party Transaction [Line Items]
Advances to affiliate		$ 171,867	$ 135,054
Related party transaction, rate		0.12%
Entity number of employees | employee		0
Related party transaction, expenses from transactions with related party		$ 100,400	102,400	$ 106,700
Cash distributions to parent		168,000	234,000	91,000
Contributions from parent		0	0	13,300
Williams Field Services [Member]
Related Party Transaction [Line Items]
Reimbursable costs		600	27,300	89,800
Related party transaction, due from (to) related party			500
Williams Partners L.P. [Member]
Related Party Transaction [Line Items]
Advances to affiliate		171,900	135,100
Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent	$ 57,000
Puget Sound Energy, Inc. [Member]
Revenue, Major Customer [Line Items]
Operating revenues		118,384	113,398	110,111
Northwest Natural Gas Company [Member]
Revenue, Major Customer [Line Items]
Operating revenues		50,857	$ 50,631	$ 51,085
Cascade Natural Gas Corporation [Member]
Revenue, Major Customer [Line Items]
Operating revenues		$ 48,363