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Fair Value Measurements and Guarantees (Tables) | 6 Months Ended
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Jun. 30, 2026
Fair Value Disclosures [Abstract] |
Fair Value Assets and Liabilities Measured On Recurring Basis [Table Text Block] | The following table presents, by level within the fair value hierarchy, certain of Williams’, Transco’s, and NWP’s significant financial assets and liabilities. The carrying values of cash and cash equivalents, accounts receivable, accounts payable, and commercial paper approximate fair value because of the short-term nature of these instruments. Therefore, these assets and liabilities are not presented in the following table.
|  |  |  |  | Fair Value Measurements Using
| Carrying Amount |  | Fair Value |  | Quoted Prices In Active Markets for Identical Assets (Level 1) |  | Significant Other Observable Inputs (Level 2) |  | Significant Unobservable Inputs (Level 3)
| (Millions)
Assets (liabilities) at June 30, 2026: |  |  |  |  |  |  |  |  |
Measured on a recurring basis: |  |  |  |  |  |  |  |  |
ARO Trust - Transco | $ | 321 |  |  | $ | 321 |  |  | $ | 321 |  |  | $ | — |  |  | $ | — |
Commodity derivative assets (1) | 266 |  |  | 631 |  |  | 392 |  |  | 98 |  |  | 141 |
Commodity derivative liabilities (1) | (309) |  |  | (919) |  |  | (536) |  |  | (213) |  |  | (170) |
Equity securities | 123 |  |  | 123 |  |  | 123 |  |  | — |  |  | — |
Additional disclosures: |  |  |  |  |  |  |  |  |
Guarantees | (34) |  |  | (26) |  |  | — |  |  | (10) |  |  | (16) |
Debt by issuer, including current portion: |  |  |  |  |  |  |  |  |
Williams | (23,300) |  |  | (22,875) |  |  | — |  |  | (22,875) |  |  | — |
Transco | (5,890) |  |  | (5,827) |  |  | — |  |  | (5,827) |  |  | — |
NWP | (749) |  |  | (747) |  |  | — |  |  | (747) |  |  | — |
MountainWest | (379) |  |  | (386) |  |  | — |  |  | (386) |  |  | — |
Total debt | (30,318) |  |  | (29,835) |  |  | — |  |  | (29,835) |  |  | — |
Assets (liabilities) at December 31, 2025: |  |  |  |  |  |  |  |  |
Measured on a recurring basis: |  |  |  |  |  |  |  |  |
ARO Trust - Transco | $ | 356 |  |  | $ | 356 |  |  | $ | 356 |  |  | $ | — |  |  | $ | — |
Commodity derivative assets (1) | 336 |  |  | 722 |  |  | 431 |  |  | 158 |  |  | 133 |
Commodity derivative liabilities (1) | (340) |  |  | (915) |  |  | (497) |  |  | (270) |  |  | (148) |
Additional disclosures: |  |  |  |  |  |  |  |  |
Guarantees | (35) |  |  | (28) |  |  | — |  |  | (12) |  |  | (16) |
Debt by issuer, including current portion: |  |  |  |  |  |  |  |  |
Williams | (21,649) |  |  | (21,556) |  |  | — |  |  | (21,556) |  |  | — |
Transco | (5,888) |  |  | (5,941) |  |  | — |  |  | (5,941) |  |  | — |
NWP | (748) |  |  | (747) |  |  | — |  |  | (747) |  |  | — |
MountainWest | (376) |  |  | (385) |  |  | — |  |  | (385) |  |  | — |
Total debt | (28,661) |  |  | (28,629) |  |  | — |  |  | (28,629) |  |  | — |
(1)The carrying amount is presented net of counterparty offsetting arrangements and collateral (see Note 8 – Commodity Derivatives).
Debt Securities, Trading, and Equity Securities, FV-NI | Investments within the ARO Trust were as follows:
|  | June 30, 2026 |  | December 31, 2025
|  | Amortized Cost Basis |  | Fair Value |  | Amortized Cost Basis |  | Fair Value
|  | (Millions)
Money market fund |  | $ | 3 |  |  | $ | 3 |  |  | $ | 34 |  |  | $ | 34 |
U.S. equity funds |  | 38 |  |  | 145 |  |  | 53 |  |  | 169 |
International equity fund |  | 32 |  |  | 58 |  |  | 32 |  |  | 51 |
Municipal bond fund |  | 117 |  |  | 115 |  |  | 104 |  |  | 102 |
Total |  | $ | 190 |  |  | $ | 321 |  |  | $ | 223 |  |  | $ | 356 |

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- Definition Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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- Definition Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-6B + Details
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