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Operating Segments - Virginia Power (Narrative) (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Segment Reporting Information [Line Items] |  |  |  |  |
Charge for expected CCRO, net of tax |  | $ 149 |  |  |
Charges associated with legislation enacted related to customer arrears, net of tax | $ 94 |  |  |  |
Virginia Electric and Power Company |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Charge for expected CCRO, net of tax |  | $ 149 |  |  |
Charges associated with legislation enacted related to customer arrears, net of tax | $ 94 |  |  |  |
Operating Segments |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
After- tax net expenses |  |  | $ 1,200 | $ 1,900 | $ 196
Operating Segments | Virginia Electric and Power Company |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
After- tax net expenses |  |  | 863 |  |
Asset early retirement expense |  |  | 751 | 346 |
Asset early retirement expense after tax |  |  | 559 | 257 |
Charge for expected CCRO |  |  | 130 |  |
Charge for expected CCRO, net of tax |  |  | 97 |  |
Charges associated with legislation enacted related to customer arrears |  |  | 127 |  |
Charges associated with legislation enacted related to customer arrears, net of tax |  |  | 94 |  |
Charge related to a voluntary retirement program |  |  |  | 198 |
Charge related to a voluntary retirement program, after-tax |  |  |  | 146 |
Asset planned early retirement expense |  |  |  | 160 |
Asset planned early retirement expense, after tax |  |  |  | 119 |
Operating revenue recorded charge |  |  |  | 135 |
Operating revenue recorded charge, after tax |  |  |  | 100 |
Cancellation abandonment expense |  |  |  | 62 |
Cancellation abandonment expense, after tax |  |  |  | 46 |
Benefit from revision of future closure costs |  |  |  | 113 |
Benefit from revision of future closure costs, after tax |  |  |  | 84 |
One-time rate credit amount |  |  |  |  | 215
One-time rate credit amount after tax |  |  |  |  | 160
Charge associated with major storm damage and service restoration |  |  |  |  | 70
Charge associated with major storm damage and service restoration, after tax |  |  |  |  | 52
Operating Segments | Virginia Electric and Power Company | Virginia Regulation |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Charge associated with asset retirement obligations for ash ponds and landfills at certain utility generation facilities |  |  |  |  | 81
Environmental remediation expense net of tax |  |  |  |  | 60
Operating Segments | Corporate and Other |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
After- tax net expenses |  |  | 3,700 | 1,800 | (117)
After- tax net expenses for specific items |  |  | 3,400 | 1,500 | (322)
Operating Segments | Corporate and Other | Virginia Electric and Power Company |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
After- tax net expenses |  |  | 863 | 634 | 312
After- tax net expenses for specific items |  |  | $ 915 | $ 627 | $ 312

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