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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, 2019 | Mar. 31, 2018
Investment Holdings [Line Items] |  |  |
Net gains (losses) recognized during the period |  | $ 414 | $ (65)
Less: Net gains recognized during the period on securities sold during the period |  | (19) | (19)
Unrealized gains (losses) recognized during the period on securities still held at March 31, 2019 and 2018 | [1] | 395 | (84)
Virginia Electric and Power Company |  |  |
Investment Holdings [Line Items] |  |  |
Net gains (losses) recognized during the period |  | 186 | (32)
Less: Net gains recognized during the period on securities sold during the period |  | (1) | (15)
Unrealized gains (losses) recognized during the period on securities still held at March 31, 2019 and 2018 | [1] | $ 185 | $ (47)
[1] | Included in other income and the nuclear decommissioning trust regulatory liability.

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- Definition Amount of realized gain 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/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=84241550&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=84241550&loc=SL75117546-209714 + Details
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- Details
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