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Credit Risk (Narrative) (Detail)
3 Months Ended
Mar. 31, 2025
USD ($)
Counterparty
Dec. 31, 2024
USD ($)
Concentration Risk and Guarantor Obligations [Line Items]    
Credit exposure $ 144,000,000  
Number of counterparties | Counterparty 0  
Amount of exposure for single counterparty $ 56,000,000  
Additional collateral to be posted if the credit related contingent features were triggered 35,000,000 $ 13,000,000
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 35,000,000 13,000,000
Letter of credit as collateral posted for derivatives in liability position 0 0
Virginia Electric and Power Company    
Concentration Risk and Guarantor Obligations [Line Items]    
Credit exposure $ 26,000,000  
Number of counterparties | Counterparty 0  
Amount of exposure for single counterparty $ 10,000,000  
Additional collateral to be posted if the credit related contingent features were triggered 33,000,000 12,000,000
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 33,000,000 12,000,000
Letter of credit as collateral posted for derivatives in liability position $ 0 $ 0
Credit Concentration Risk | Investment Grade Counterparty | Virginia Electric and Power Company    
Concentration Risk and Guarantor Obligations [Line Items]    
Concentration risk, percentage (percentage) 32.00%  
Credit Concentration Risk | Investment Grade | Investment Grade Counterparty    
Concentration Risk and Guarantor Obligations [Line Items]    
Concentration risk, percentage (percentage) 85.00%