Fair Value Measurements - ARO Trust (Details) - Transcontinental Gas Pipe Line Company, LLC [Member] - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI, Cost	$ 213	$ 200
Debt Securities, Trading, and Equity Securities, FV-NI	323	297
External Trust
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transco's annual funding commitment for ARO	64
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	24	27
Debt Securities, Trading, and Equity Securities, FV-NI	24	27
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	53	53
Debt Securities, Trading, and Equity Securities, FV-NI	153	146
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	47	40
Municipal Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI, Cost	104	88
Debt Securities, Trading, and Equity Securities, FV-NI	$ 99	$ 84

Cost of investment in debt investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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