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Credit Risk (Narrative) (Detail)
12 Months Ended
Dec. 31, 2023
USD ($)
Counterparty
Dec. 31, 2022
USD ($)
Concentration Risk and Guarantor Obligations [Line Items]    
Credit exposure $ 340,000,000  
Amount of exposure for single counterparty $ 80,000,000  
Number of counterparties | Counterparty 0  
Letter of credit as collateral posted for derivatives in liability position   $ 20,000,000
Additional collateral to be posted if the credit related contingent features were triggered $ 28,000,000 140,000,000
Collateral derivatives with credit-related contingent provision in a liability position 0 72,000,000
Aggregate fair value of all derivative instruments with credit contingent provisions that are in a liability position 28,000,000 212,000,000
Maximum    
Concentration Risk and Guarantor Obligations [Line Items]    
Letter of credit as collateral posted for derivatives in liability position 1,000,000  
Virginia Electric and Power Company    
Concentration Risk and Guarantor Obligations [Line Items]    
Credit exposure 129,000,000  
Amount of exposure for single counterparty $ 22,000,000  
Number of counterparties | Counterparty 0  
Letter of credit as collateral posted for derivatives in liability position   20,000,000
Additional collateral to be posted if the credit related contingent features were triggered $ 14,000,000 28,000,000
Collateral derivatives with credit-related contingent provision in a liability position 0 72,000,000
Aggregate fair value of all derivative instruments with credit contingent provisions that are in a liability position 14,000,000 $ 99,000,000
Virginia Electric and Power Company | Maximum    
Concentration Risk and Guarantor Obligations [Line Items]    
Letter of credit as collateral posted for derivatives in liability position $ 1,000,000  
Credit Concentration Risk | Investment Grade Counterparty | Virginia Electric and Power Company    
Concentration Risk and Guarantor Obligations [Line Items]    
Concentration risk, percentage (percentage) 83.00%  
Credit Concentration Risk | Investment Grade | Investment Grade Counterparty    
Concentration Risk and Guarantor Obligations [Line Items]    
Concentration risk, percentage (percentage) 89.00%