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Income Taxes (Income Tax Expense for Continuing Operations Including Noncontrolling Interests) (Parenthetical) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Income Tax Contingency [Line Items] |  |  |  |
Tax Reform Act Expense | [1] |  | $ 46 | $ (851)
Dominion Energy Gas Holdings, LLC |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |
Tax Reform Act Expense | [1] |  | (6) | $ (246)
Discontinued Operations [Member] | Dominion Energy Gas Holdings, LLC |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |
Tax Reform Act Expense |  | $ 93 | $ 8 |
[1] | The 2017 Tax Reform Act impact for Dominion Energy Gas includes an expense of $8 million for the year ended December 31, 2018 and a benefit of $93 million for the year ended December 31, 2017 arising from discontinued operations.

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- Definition Amount of income tax expense (benefit) for remeasurement of deferred tax from change in tax rate pursuant to Tax Cuts and Jobs Act. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319 + Details
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