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Significant Accounting Policies (Schedule of Supplemental Cash Flow Information) (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Schedule Of Supplemental Cash Flow Information [Line Items]      
Financing leases $ 47 $ 46 $ 113
Operating leases 49 127 44
Virginia Electric and Power Company      
Schedule Of Supplemental Cash Flow Information [Line Items]      
Financing leases 37 $ 32 20
Operating leases $ 42   $ 35