Income Taxes (Reconciliation of Income Taxes at the U.S. Statutory Federal Income Tax Rate) (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Computation [Line Items]
U.S. statutory rate	21.00%	35.00%	35.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	3.00%	2.00%	2.40%
Investment tax credits	(1.90%)	(6.30%)	(11.70%)
Production tax credits	(0.70%)	(0.70%)	(0.80%)
Valuation allowances	0.30%	0.20%	1.20%
Reversal of excess deferred income taxes	(2.00%)
Federal legislative change	1.50%	(27.50%)
State legislative change	(0.60%)		(0.60%)
AFUDC-equity	(0.80%)	(1.40%)	(0.60%)
Employee stock ownership plan deduction	(0.40%)	(0.60%)	(0.60%)
Other, net	(0.90%)	(1.70%)	(1.40%)
Effective tax rate	18.50%	(1.00%)	22.90%
Virginia Electric and Power Company
Effective Income Tax Computation [Line Items]
U.S. statutory rate	21.00%	35.00%	35.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	4.70%	3.70%	3.80%
Investment tax credits	(3.50%)	(0.80%)
Production tax credits	(0.70%)	(0.40%)	(0.50%)
Valuation allowances			0.10%
Reversal of excess deferred income taxes	(3.20%)
Federal legislative change	1.30%	(4.00%)
AFUDC-equity	(0.50%)	(0.60%)	(0.60%)
Other, net	(0.10%)	0.60%	(0.40%)
Effective tax rate	19.00%	33.50%	37.40%
Dominion Energy Gas Holdings, LLC
Effective Income Tax Computation [Line Items]
U.S. statutory rate	21.00%	35.00%	35.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	3.20%	2.40%	0.50%
Valuation allowances	1.80%	0.30%
Reversal of excess deferred income taxes	(1.70%)
Federal legislative change	(2.80%)	(29.50%)
State legislative change	0.20%
AFUDC-equity	(0.60%)	(0.90%)	(0.20%)
Other, net	1.20%	0.40%	0.10%
Effective tax rate	22.30%	7.70%	35.40%