Statement of Cash Flows (Unaudited) - NWP - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024
Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract]
Net income	$ 1,995	$ 1,829
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract]
Depreciation, depletion, and amortization	1,754	1,654
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract]
Increase (Decrease) in Inventories	(66)	(6)
Increase (Decrease) in Other Current Assets	(43)	(16)
Other current liabilities	95	(108)
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Other Item	(128)	(200)
Net cash provided (used) by operating activities	4,322	3,756
Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract]
Net cash provided (used) by financing activities	(1,110)	(1,351)
Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract]
Capital expenditures (1)	(2,938)	(1,805)
Net cash provided (used) by investing activities	(3,202)	(3,793)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect, Total	10	(1,388)
Cash and cash equivalents at beginning of year	60	2,150
Cash and cash equivalents at end of period	70	762
Additional Cash Flow Elements and Supplemental Cash Flow Information [Abstract]
Property, Plant and Equipment, Additions	(3,079)	(1,840)
Capital expenditures	(2,938)	(1,805)
Northwest Pipeline LLC [Member]
Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract]
Net income	135	134
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract]
Depreciation, depletion, and amortization	88	82
Increase (Decrease) in Allowance for Equity Funds Used During Construction	(6)	(7)
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract]
Increase (Decrease) in Accounts and Other Receivables	3	6
Increase (Decrease) in Other Current Assets	1	0
Increase (Decrease) in Accounts Payable, Trade	(6)	(4)
Increase (Decrease) in Accounts Payable, Related Parties	(3)	(3)
Other current liabilities	9	15
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Other Item	(40)	(23)
Net cash provided (used) by operating activities	181	200
Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract]
Cash distributions to parent	(106)	(113)
Cash contributions from parent	181	0
Increase Decrease In Advances From Affiliates	(26)	0
Net cash provided (used) by financing activities	49	(113)
Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract]
Capital expenditures (1)	(149)	(178)
Contributions in aid of construction	6	5
Payments for (Proceeds from) Removal Costs	(17)	(9)
IncreaseDecreaseInAdvancesToAffiliates	(70)	95
Net cash provided (used) by investing activities	(230)	(87)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect, Total	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	0	0
Additional Cash Flow Elements and Supplemental Cash Flow Information [Abstract]
Property, Plant and Equipment, Additions	(170)	(213)
Increase (Decrease) in Accounts Payable And Accrued Liabilities Related To Capital Expenditures	21	35
Capital expenditures	$ (149)	$ (178)

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