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Fair Value Measurements (Narrative) (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2024
Jun. 30, 2024
Sep. 30, 2023
Jun. 30, 2023
Mar. 31, 2023
Sep. 30, 2024
Sep. 30, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Unrealized gains (losses) included in operating revenue in Level 3 fair value category $ 12,000,000   $ (10,000,000)     $ 7,000,000 $ (8,000,000)
Impairment of assets and other charges 122,000,000   1,000,000     219,000,000 136,000,000
Level 2 | Nonregulated Solar Assets              
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Long-lived assets, estimated fair value       $ 22,000,000      
Impairment of Assets and Other Charges | Nonregulated Solar Assets              
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Impairment of assets and other charges       15,000,000      
Asset impairment charges after tax       $ 11,000,000      
Impairment of Assets and Other Charges | Corporate Office Building              
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Impairment of assets and other charges   $ 17,000,000     $ 91,000,000    
Asset impairment charges after tax   $ 12,000,000     $ 68,000,000    
Virginia Electric and Power Company              
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Unrealized gains (losses) included in operating revenue in Level 3 fair value category 0   $ 0     $ 0 $ 0
Virginia Electric and Power Company | Impairment of Assets and Other Charges              
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]              
Impairment of assets and other charges 25,000,000            
Asset impairment charges after tax $ 18,000,000