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Related-Party Transactions (Parenthetical) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Related Party Transaction [Line Items]        
Capital expenditures     $ 2,112 $ 2,046
Virginia Electric and Power Company        
Related Party Transaction [Line Items]        
Capital expenditures     1,079 1,170
Virginia Electric and Power Company | Services provided by affiliates | Affiliated Entity        
Related Party Transaction [Line Items]        
Capital expenditures $ 34 $ 38 67 75
Dominion Energy Gas Holdings, LLC        
Related Party Transaction [Line Items]        
Capital expenditures     292 316
Dominion Energy Gas Holdings, LLC | Services provided by affiliates | Affiliated Entity        
Related Party Transaction [Line Items]        
Capital expenditures $ 7 $ 7 $ 12 $ 17