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Investments (Selected Information Regarding Equity and Fixed Income Securities) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Proceeds from sales |  | $ 4,278 | $ 1,712 | $ 1,804
Realized gains | [1] | 340 | 195 | 140
Realized losses | [1] | 297 | 96 | 91
Virginia Electric and Power Company |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Proceeds from sales |  | 884 | 858 | 887
Realized gains | [1] | 88 | 58 | 60
Realized losses | [1] | $ 68 | $ 22 | $ 27
[1] | Includes realized gains and losses recorded to the nuclear decommissioning trust regulatory liability as discussed in Note 2.

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