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Goodwill and Intangible Assets (Annual Amortization Expense of Intangible Assets) (Detail)
$ in Millions
Dec. 31, 2019
USD ($)
Finite-Lived Intangible Assets [Line Items]  
2020 $ 88
2021 78
2022 70
2023 56
2024 49
Virginia Electric and Power Company  
Finite-Lived Intangible Assets [Line Items]  
2020 25
2021 19
2022 15
2023 8
2024 6
Dominion Energy Gas Holdings, LLC  
Finite-Lived Intangible Assets [Line Items]  
2020 9
2021 8
2022 8
2023 5
2024 $ 4