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Related Party Transactions (Tables) | 9 Months Ended
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Sep. 30, 2025
Related Party Transactions [Abstract] |
Schedule of Related Party Transactions | Transco and NWP are participants in Williams’ cash management program, and thus make advances to and receive advances from Williams. Advances to Williams are represented by demand notes and are classified as Trade accounts and other receivables - Advances to affiliate in the Balance Sheet. Advances from Williams are classified as Payables - Advances from affiliate. Advances are stated at the historical carrying amounts.
| September 30, |  | December 31, |
| 2025 |  | 2024 |  |
| (Millions) |  |
Advances to affiliate |  |  |  |  |
Transco | $ | 498 |  |  | $ | 638 |  |  |
NWP | 70 |  |  | — |  |  |
Advances from affiliate |  |  |  |  |
NWP | $ | — |  |  | $ | 26 |  |  |
Interest expense and income are recognized when earned and the collectability is reasonably assured. The interest rate on intercompany demand notes is based upon the daily overnight investment rate paid on Williams’ excess cash at the end of each month, which was approximately 4 percent at September 30, 2025. Interest income is included in Interest income in the Statement of Net Income for Transco and Other income (expense) – net in the Statement of Net Income for NWP.
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2025 |  | 2024 |  | 2025 |  | 2024
| (Millions)
Net interest income from advances |  |  |  |  |  |  |
Transco | $ | 6 |  |  | $ | 12 |  |  | $ | 18 |  |  | $ | 42 |
NWP | 1 |  |  | 1 |  |  | 2 |  |  | 5 |
Revenues received from affiliates are included in Transco’s Total revenues in the Statement of Net Income. Costs of gas purchased from affiliates are included in Transco’s Natural gas product costs in the Statement of Net Income. All gas purchases are made at market or contracted prices.
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2025 |  | 2024 |  | 2025 |  | 2024
| (Millions)
Transco affiliate activity |  |  |  |  |  |  |
Total revenues | $ | 21 |  |  | $ | 20 |  |  | $ | 63 |  |  | $ | 57 |
Natural gas product costs | 2 |  |  | 1 |  |  | 7 |  |  | 4 |
Services necessary to operate Transco and NWP are provided by Williams and certain affiliates of Williams. Transco and NWP reimburse Williams and its affiliates for all direct and indirect expenses incurred or payments made (including salary, bonus, incentive compensation, and benefits) in connection with these services. Employees of Williams also provide general, administrative, and management services, and Transco and NWP are charged for certain administrative expenses incurred by Williams. These charges are either directly assigned or allocated. Allocated charges are specific or general. Specific allocations are based on a relationship with the delivery of services and general allocations are based on a three-factor formula, which considers revenues; property, plant, and equipment; and payroll. In management’s estimation, the allocation methodologies used are reasonable and result in a reasonable allocation of costs of doing business incurred by Williams. Transco and NWP have recorded for these service expenses, which are primarily included in Operating and maintenance expenses and Selling, general, and administrative expenses in the Statement of Net Income.
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2025 |  | 2024 |  | 2025 |  | 2024
| (Millions)
Services with affiliates |  |  |  |  |  |  |
Transco | $ | 88 |  |  | $ | 94 |  |  | $ | 262 |  |  | $ | 254 |
NWP | 23 |  |  | 25 |  |  | 68 |  |  | 68 |
During October 2025, NWP declared and paid cash distributions of $42 million to Williams, and Williams made a cash contribution to NWP of $50 million.

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- Definition Tabular disclosure of related party transactions. Examples of related party transactions include, but are not limited to, transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners and (d) affiliates. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 850 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483326/850-10-50-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 850 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483326/850-10-50-1 + Details
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