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Investments (Selected Information Regarding Equity and Fixed Income Securities) (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Proceeds from sales |  | $ 1,208 | $ 429 | $ 2,868 | $ 1,311
Realized gains | [1] | 48 | 53 | 188 | 152
Realized losses | [1] | 29 | 25 | 159 | 75
Virginia Electric and Power Company |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Proceeds from sales |  | 164 | 230 | 694 | 677
Realized gains | [1] | 18 | 21 | 73 | 46
Realized losses | [1] | $ 10 | $ 6 | $ 58 | $ 18
[1] | Includes realized gains and losses recorded to the nuclear decommissioning trust regulatory liability.

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