Balance Sheet (Unaudited) - NWP - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Assets, Current [Abstract]
Cash and cash equivalents	$ 903	$ 60
Inventory, Net	335	279
Other current assets and deferred charges	218	192
Current assets	3,221	2,661
Property, Plant and Equipment, Gross	59,391	57,395
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(19,618)	(18,703)
Property, Plant and Equipment, Net	39,773	38,692
Other Assets, Noncurrent	1,838	1,830
Total assets	56,141	54,532
Liabilities, Current [Abstract]
Accounts payable	1,414	1,613
Other current liabilities	1,521	1,360
Total current liabilities	6,012	5,312
Contingent liabilities and commitments
Members' Equity [Abstract]
Retained Earnings (Accumulated Deficit)	(12,387)	(12,396)
Total liabilities and equity	56,141	54,532
Northwest Pipeline LLC [Member]
Assets, Current [Abstract]
Cash and cash equivalents	0	0
Accounts and Other Receivables, Net, Current	1	2
Inventory, Net	9	9
Regulatory Assets, Current	4	6
Other current assets and deferred charges	4	6
Current assets	119	62
Property, Plant and Equipment, Gross	4,312	4,218
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(2,139)	(2,089)
Property, Plant and Equipment, Net	2,173	2,129
Regulatory Assets, Noncurrent	63	49
Other Assets, Noncurrent	31	29
Total assets	2,386	2,269
Liabilities, Current [Abstract]
Accounts Payable, Trade, Current	45	48
Regulatory Liability, Current	20	20
Other current liabilities	29	34
Long-Term Debt, Current Maturities	85	85
Total current liabilities	187	225
Long-Term Debt, Excluding Current Maturities	498	497
Regulatory Liabilities, Noncurrent	226	233
Asset Retirement Obligations, Noncurrent	148	144
Other Liabilities, Noncurrent	6	7
Contingent liabilities and commitments
Members' Equity [Abstract]
Members' Capital	1,205	1,074
Retained Earnings (Accumulated Deficit)	116	89
Total Members' Equity	1,321	1,163
Total liabilities and equity	2,386	2,269
Northwest Pipeline LLC [Member] | Related Party
Assets, Current [Abstract]
Accounts and Financing Receivable, after Allowance for Credit Loss, Current	64	0
Liabilities, Current [Abstract]
Accounts payable	8	12
Northwest Pipeline LLC [Member] | Nonrelated Party
Assets, Current [Abstract]
Accounts Receivable, after Allowance for Credit Loss, Current	37	39
Northwest Pipeline LLC [Member] | Affiliated Entity
Liabilities, Current [Abstract]
Accounts payable	$ 0	$ 26