Income Taxes (Income Tax Expense for Continuing Operations Including Noncontrolling Interests) (Parenthetical) (Detail) - USD ($) $ in Millions		12 Months Ended
		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.