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Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]      
Net gains (losses) recognized during the period $ 1,020 $ 811 $ (848)
Less: Net (gains) losses recognized during the period on securities sold during the period (16) (7) 8
Unrealized gains (losses) recognized during the period on securities still held at period end [1] 1,004 804 (840)
Virginia Electric and Power Company      
Debt Securities, Available-for-Sale [Line Items]      
Net gains (losses) recognized during the period 532 420 (436)
Less: Net (gains) losses recognized during the period on securities sold during the period (11) 7 (7)
Unrealized gains (losses) recognized during the period on securities still held at period end [1] $ 521 $ 427 $ (443)
[1] Included in other income (expense) and the nuclear decommissioning trust regulatory liability as discussed in Note 2.