Transactions with Major Customers and Affiliates (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Feb. 28, 2021 USD ($)	Dec. 31, 2020 USD ($) employee	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Related Party Transaction [Line Items]
Advances to affiliate		$ 247,869	$ 201,265
Related party transaction, rate		0.01%
Interest Income, affiliate		$ 600	4,100	$ 2,000
Entity number of employees | employee		0
Related party transaction, expenses from transactions with related party		$ 82,700	96,200	92,700
Cash distributions to parent		(164,000)	(110,000)	(174,000)
Williams Companies Inc [Member]
Related Party Transaction [Line Items]
Advances to affiliate		247,900	201,300
Cash distributions to parent		164,000	110,000	174,000
Subsequent Event [Member]
Related Party Transaction [Line Items]
Cash distributions to parent	$ 55,000
Puget Sound Energy, Inc.
Revenue, Major Customer [Line Items]
Operating revenues		132,747	121,792	115,238
Northwest Natural Gas Company
Revenue, Major Customer [Line Items]
Operating revenues		48,893	48,891	49,126
Cascade Natural Gas Corporation
Revenue, Major Customer [Line Items]
Operating revenues		$ 47,493	$ 46,969	$ 46,164