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Credit Risk (Narrative) (Detail)
3 Months Ended
Mar. 31, 2024
USD ($)
Counterparty
Dec. 31, 2023
USD ($)
Concentration Risk and Guarantor Obligations [Line Items]    
Credit exposure $ 274,000,000  
Number of counterparties | Counterparty 0  
Amount of exposure for single counterparty $ 80,000,000  
Additional collateral to be posted if the credit related contingent features were triggered 32,000,000 $ 28,000,000
Collateral derivatives with credit-related contingent provision in a liability position 0 0
Aggregate fair value of all derivative instruments with credit contingent provisions that are in a liability position 32,000,000 28,000,000
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 $ 107,000,000  
Number of counterparties | Counterparty 0  
Amount of exposure for single counterparty $ 23,000,000  
Additional collateral to be posted if the credit related contingent features were triggered 24,000,000 14,000,000
Collateral derivatives with credit-related contingent provision in a liability position 0 0
Aggregate fair value of all derivative instruments with credit contingent provisions that are in a liability position $ 24,000,000 14,000,000
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) 73.00%  
Credit Concentration Risk | Investment Grade | Investment Grade Counterparty    
Concentration Risk and Guarantor Obligations [Line Items]    
Concentration risk, percentage (percentage) 86.00%