Income Taxes (Reconciliation of Income Taxes at the U.S. Statutory Federal Income Tax Rate) (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 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	0.20%	3.30%
Investment tax credits	(5.70%)	(0.90%)
Production tax credits	(1.20%)	(0.70%)
Reversal of excess deferred income taxes	(6.80%)	(1.50%)
Federal legislative change		2.00%
State legislative change		(0.80%)
Write-off of regulatory assets	33.50%
AFUDC - equity	(2.00%)	(0.90%)
Other, net	(2.70%)	(1.00%)
Effective tax rate	36.30%	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	4.50%	4.60%
Investment tax credits	(5.30%)	(1.40%)
Production tax credits	(0.80%)	(0.70%)
Reversal of excess deferred income taxes	(4.10%)	(1.90%)
Federal legislative change		(0.20%)
AFUDC - equity		(0.50%)
Other, net	(1.20%)	(0.30%)
Effective tax rate	14.10%	20.60%
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	4.20%	3.90%
Reversal of excess deferred income taxes	(1.10%)	(1.30%)
Federal legislative change		2.00%
State legislative change		0.10%
AFUDC - equity	(0.60%)	(0.40%)
Other, net	(1.30%)	0.70%
Effective tax rate	22.20%	26.00%