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Fair Value Measurements (Narrative) (Detail) - USD ($) | 3 Months Ended
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Mar. 31, 2020 | Mar. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Unrealized gains or losses included in earnings in Level 3 fair value category | $ 0 | $ 0
Virginia Electric and Power Company |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Unrealized gains or losses included in earnings in Level 3 fair value category | $ 0 | $ 0

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- Definition Amount of gain (loss) recognized in income from asset and liability measured at fair value on recurring basis using unobservable input (level 3). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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