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Related-Party Transactions (Parenthetical) (Detail) - Virginia Electric and Power Company - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Related Party Transaction [Line Items]      
Capital expenditures $ 3,521 $ 3,138 $ 2,642
Services provided by affiliates | Affiliated Entity      
Related Party Transaction [Line Items]      
Capital expenditures $ 161 $ 141 $ 133