Transactions with Major Customers and Affiliates (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) employee	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Related Party Transaction [Line Items]
Advances to affiliate		$ 201,265	$ 180,400
Related party transaction, rate		1.49%
Interest Income, affiliate		$ 4,100	2,000	$ 800
Entity number of employees | employee		0
Related party transaction, expenses from transactions with related party		$ 96,200	92,700	96,500
Cash distributions to parent		(110,000)	(174,000)	(186,000)
Williams Companies Inc [Member]
Related Party Transaction [Line Items]
Advances to affiliate		201,300	180,400
Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent	$ (45,000)
Puget Sound Energy, Inc.
Revenue, Major Customer [Line Items]
Operating revenues		121,792	115,238	120,226
Northwest Natural Gas Company
Revenue, Major Customer [Line Items]
Operating revenues		48,891	49,126	51,743
Cascade Natural Gas Corporation
Revenue, Major Customer [Line Items]
Operating revenues		$ 46,969	$ 46,164	$ 48,071