Income Taxes (Reconciliation of Income Taxes at the U.S. Statutory Federal Income Tax Rate) (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Effective Income Tax Computation [Line Items]
U.S. statutory rate	21.00%	21.00%	35.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	2.20%	4.10%
Investment tax credits	(1.50%)	(0.50%)
Production tax credits	(0.80%)	(0.60%)
Reversal of excess deferred income taxes	(5.10%)	(1.40%)
Write-off of regulatory assets	(34.10%)
Other, net	(2.00%)	(2.10%)
Effective tax rate	(20.30%)	20.50%
Virginia Electric and Power Company
Effective Income Tax Computation [Line Items]
U.S. statutory rate	21.00%	21.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	4.60%	4.50%
Investment tax credits	(3.20%)	(0.90%)
Production tax credits	(1.00%)	(0.70%)
Reversal of excess deferred income taxes	(5.00%)	(2.00%)
Other, net	0.10%	(0.30%)
Effective tax rate	16.50%	21.60%
Dominion Energy Gas Holdings, LLC
Effective Income Tax Computation [Line Items]
U.S. statutory rate	21.00%	21.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	3.40%	4.30%
Reversal of excess deferred income taxes	(1.10%)	(1.00%)
Other, net	(0.30%)	(0.40%)
Effective tax rate	23.00%	23.90%