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Goodwill and Intangible Assets (Components of Intangible Assets) (Detail) - Computer Software, Intangible Asset [Member] - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount $ 1,340 $ 1,033
Accumulated Amortization 549 363
Virginia Electric and Power Company    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 406 384
Accumulated Amortization 135 134
Dominion Energy Gas Holdings, LLC    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 178 179
Accumulated Amortization $ 72 $ 64