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Credit Risk (Narrative) (Detail)
6 Months Ended
Jun. 30, 2023
USD ($)
Counterparty
Dec. 31, 2022
USD ($)
Concentration Risk and Guarantor Obligations [Line Items]    
Credit exposure $ 208,000,000  
Additional collateral to be posted if the credit related contingent features were triggered 89,000,000 $ 140,000,000
Collateral derivatives with credit-related contingent provision in a liability position 1,000,000  
Aggregate fair value of all derivative instruments with credit contingent provisions that are in a liability position 90,000,000 212,000,000
Virginia Electric and Power Company    
Concentration Risk and Guarantor Obligations [Line Items]    
Credit exposure 63,000,000  
Additional collateral to be posted if the credit related contingent features were triggered 35,000,000 28,000,000
Collateral derivatives with credit-related contingent provision in a liability position 0 72,000,000
Letter of credit as collateral posted for derivatives in liability position 4,000,000 20,000,000
Aggregate fair value of all derivative instruments with credit contingent provisions that are in a liability position $ 35,000,000 $ 99,000,000
Credit Concentration Risk    
Concentration Risk and Guarantor Obligations [Line Items]    
Number of counterparties | Counterparty 0  
Amount of exposure for single counterparty $ 47,000,000  
Credit Concentration Risk | Virginia Electric and Power Company    
Concentration Risk and Guarantor Obligations [Line Items]    
Number of counterparties | Counterparty 0  
Amount of exposure for single counterparty $ 12,000,000  
Credit Concentration Risk | Investment Grade Counterparty | Virginia Electric and Power Company    
Concentration Risk and Guarantor Obligations [Line Items]    
Concentration risk, percentage (percentage) 75.00%  
Credit Concentration Risk | Investment Grade | Investment Grade Counterparty    
Concentration Risk and Guarantor Obligations [Line Items]    
Concentration risk, percentage (percentage) 86.00%