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Fair Value Measurements - ARO Trust (Details) - Transcontinental Gas Pipe Line Company, LLC [Member] - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Trading, and Equity Securities, FV-NI, Cost $ 200 $ 198
Debt Securities, Trading, and Equity Securities, FV-NI 297 269
External Trust    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Transco's annual funding commitment for ARO 16  
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 27 26
Debt Securities, Trading, and Equity Securities, FV-NI 27 26
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 146 120
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 40 39
Municipal Bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt Securities, Trading, and Equity Securities, FV-NI, Cost 88 87
Debt Securities, Trading, and Equity Securities, FV-NI $ 84 $ 84