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Operating Revenue (Narrative) (Detail) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2024
Revenues From Contract With Customer [Line Items]      
Contract liability balances $ 45   $ 52
Revenue recognized from contract liability balances 50 $ 45  
Virginia Electric and Power Company      
Revenues From Contract With Customer [Line Items]      
Contract liability balances 38   $ 46
Revenue recognized from contract liability balances $ 46 $ 40