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Asset Retirement Obligations (Changes to AROs) (Parenthetical) (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Asset Retirement Obligations [Line Items]      
Asset retirement obligation, liabilities incurred $ 31 $ 67  
Property, plant and equipment, net, decrease 173    
Other Current Liabilities      
Asset Retirement Obligations [Line Items]      
Asset retirement obligations 198 179  
Other Operations and Maintenance      
Asset Retirement Obligations [Line Items]      
Asset retirement obligation, liabilities incurred 44    
Asset retirement obligation, liabilities incurred after tax 35    
Virginia Electric and Power Company      
Asset Retirement Obligations [Line Items]      
Asset retirement obligations 191 166  
Asset retirement obligation, liabilities incurred $ 26 $ 48  
Virginia Electric and Power Company | Other Operations and Maintenance      
Asset Retirement Obligations [Line Items]      
Asset retirement obligation, liabilities incurred     $ 113
ARO incurred, after tax     $ 84