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Operating Revenue (Narrative) (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Revenues From Contract With Customer [Line Items]    
Revenue recognized from contract liability balances $ 124 $ 97
Other Current Liabilities and Other Deferred Credits and Other Liabilities    
Revenues From Contract With Customer [Line Items]    
Contract liability balances 124 130
Virginia Electric and Power Company    
Revenues From Contract With Customer [Line Items]    
Revenue recognized from contract liability balances 36 24
Virginia Electric and Power Company | Other Current Liabilities and Other Deferred Credits and Other Liabilities    
Revenues From Contract With Customer [Line Items]    
Contract liability balances $ 33 $ 36