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Related-Party Transactions (Detail) - Virginia Electric and Power Company - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Related Party Transaction [Line Items]    
Commodity purchases from affiliates $ 181 $ 211
Services provided by affiliates [1] 125 121
Affiliated Entity    
Related Party Transaction [Line Items]    
Services provided to affiliates $ 5 $ 5
[1] Includes capitalized expenditures of $38 million and $34 million for the three months ended March 31, 2021 and 2020, respectively.