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Related-Party Transactions (Parenthetical) (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Related Party Transaction [Line Items]      
Capital expenditures $ 4,980 $ 4,254 $ 5,504
Virginia Electric and Power Company      
Related Party Transaction [Line Items]      
Capital expenditures 2,642 2,228 2,496
Virginia Electric and Power Company | Services provided by affiliates | Affiliated Entity      
Related Party Transaction [Line Items]      
Capital expenditures 133 145 144
Dominion Energy Gas Holdings, LLC      
Related Party Transaction [Line Items]      
Capital expenditures 704 1,109 1,815
Dominion Energy Gas Holdings, LLC | Services provided by affiliates | Affiliated Entity      
Related Party Transaction [Line Items]      
Capital expenditures $ 19 $ 37 $ 53