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Investments (Portion of Unrealized Gains and Losses Relates to Equity Securities) (Detail) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2020 | Mar. 31, 2019
Investment Holdings [Line Items] |  |  |
Net gains (losses) recognized during the period |  | $ (898) | $ 414
Less: Net (gains) losses recognized during the period on securities sold during the period |  | 14 | (19)
Unrealized gains (losses) recognized during the period on securities still held at March 31, 2020 and 2019 | [1] | (884) | 395
Virginia Electric and Power Company |  |  |
Investment Holdings [Line Items] |  |  |
Net gains (losses) recognized during the period |  | (423) | 186
Less: Net (gains) losses recognized during the period on securities sold during the period |  | 6 | (1)
Unrealized gains (losses) recognized during the period on securities still held at March 31, 2020 and 2019 | [1] | $ (417) | $ 185
[1] | Included in other income and the nuclear decommissioning trust regulatory liability.

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- Definition Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714 + Details
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- Definition Amount of realized gain (loss) from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714 + Details
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- Definition Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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