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Fair Value Measurements (Net Change in the Assets and Liabilities Measured at Fair Value on a Recurring Basis and Included in the Level 3 Fair Value Category) (Detail) - Commodity - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2023
Mar. 31, 2022
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Beginning balance $ 422 $ 222
Total realized and unrealized gains (losses):    
Included in earnings (51) $ 48
Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]   Electric fuel and other energy-related purchases
Included in regulatory assets/liabilities (216) $ 20
Settlements 35 (48)
Purchases 16  
Ending balance 206 202
Virginia Electric and Power Company    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Beginning balance 221 102
Total realized and unrealized gains (losses):    
Included in earnings (52) $ 45
Fair Value, Net Derivative Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]   Electric fuel and other energy-related purchases
Included in regulatory assets/liabilities (166) $ 80
Settlements 36 (45)
Purchases 16  
Ending balance $ 55 $ 22