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Long-Term Debt (Based on Stated Maturity Dates Rather than Early Redemption Dates that Could be Elected by Instrument Holders) (Parenthetical) (Detail) - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Feb. 28, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]        
Repayment of Debt   $ 9,116 $ 5,682 $ 1,572
Term loans        
Debt Instrument [Line Items]        
Estimated mandatory prepayments due within one year   $ 20    
Dominion Energy Midstream Partners, LP        
Debt Instrument [Line Items]        
Repayment of outstanding credit facility balance $ 73      
Variable Rate Term Loan | Dominion Energy Midstream Partners, LP        
Debt Instrument [Line Items]        
Repayment of Debt $ 300