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Fair Value Measurements - ARO Trust (Details) - Transcontinental Gas Pipe Line Company, LLC [Member] - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI, Cost	$ 190	$ 223
Debt Securities, Trading, and Equity Securities, FV-NI	321	356
External Trust
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transco's annual funding commitment for ARO	51
Cash management funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI, Cost	3	34
Debt Securities, Trading, and Equity Securities, FV-NI	3	34
Private Equity Funds, US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI, Cost	38	53
Debt Securities, Trading, and Equity Securities, FV-NI	145	169
Private Equity Funds, Non-US
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI, Cost	32	32
Debt Securities, Trading, and Equity Securities, FV-NI	58	51
Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI, Cost	117	104
Debt Securities, Trading, and Equity Securities, FV-NI	$ 115	$ 102

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