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Fair Value Measurements (Narrative) (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2022
Jun. 30, 2021
Jun. 30, 2022
Jun. 30, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Unrealized gains or losses included in operating revenue in Level 3 fair value category $ 0 $ (2,000,000) $ 0 $ (2,000,000)
Virginia Electric and Power Company        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Unrealized gains or losses included in operating revenue in Level 3 fair value category $ 0 0 $ 0 0
Virginia Electric and Power Company | Level 2 | Nonregulated Retail Software Development | Maximum        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Long-lived assets, estimated fair value   1,000,000   $ 1,000,000
Virginia Electric and Power Company | Impairment of Assets and Other Charges | Nonregulated Retail Software Development        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Impairment of assets and other charges (benefits)   20,000,000    
Asset impairment charges after tax   $ 15,000,000