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Related-Party Transactions (Detail) - Virginia Electric and Power Company - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Related Party Transaction [Line Items]      
Commodity purchases from affiliates $ 569 $ 690 $ 930
Services provided by affiliates [1] 455 503 450
Affiliated Entity      
Related Party Transaction [Line Items]      
Services provided to affiliates $ 18 $ 24 $ 24
[1] Includes capitalized expenditures of $141 million, $133 million and $145 million for the year ended December 31, 2020, 2019 and 2018, respectively.