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Fair Value Measurements (Net Change in the Assets and Liabilities Measured at Fair Value on a Recurring Basis and Included in the Level 3 Fair Value Category) (Detail) - Commodity - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Beginning balance $ 64 $ 150
Total realized and unrealized gains (losses):    
Included in other comprehensive income   1
Included in regulatory assets/liabilities 7 (21)
Settlements (1) 7
Purchases (10)  
Transfers out of Level 3 (2) 1
Ending balance 53 120
Virginia Electric and Power Company    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Beginning balance 60 147
Total realized and unrealized gains (losses):    
Included in regulatory assets/liabilities 8 (19)
Settlements (5) 6
Ending balance 59 117
Dominion Energy Gas Holdings, LLC    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]    
Beginning balance   (2)
Total realized and unrealized gains (losses):    
Included in other comprehensive income   1
Transfers out of Level 3   1
Ending balance   0
Operating Revenue    
Total realized and unrealized gains (losses):    
Included in earnings (1) (1)
Electric Fuel and Other Energy-Related Purchases    
Total realized and unrealized gains (losses):    
Included in earnings (4) (17)
Electric Fuel and Other Energy-Related Purchases | Virginia Electric and Power Company    
Total realized and unrealized gains (losses):    
Included in earnings $ (4) $ (17)