v3.26.1
Fair Value Measurements (Narrative) (Detail) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Unrealized gains (losses) included in earnings in Level 3 fair value category $ (20,000,000) $ (3,000,000) $ (30,000,000) $ 10,000,000
Virginia Electric and Power Company        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Unrealized gains (losses) included in earnings in Level 3 fair value category $ 0 $ 0 $ 0 $ 0