Income Taxes (Reconciliation of Income Taxes at the U.S. Statutory Federal Income Tax Rate) (Detail)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Effective Income Tax Computation [Line Items]
U.S. statutory rate	21.00%	21.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	3.50%	3.30%
Investment tax credits	(3.80%)	(7.00%)
Production tax credits	(0.30%)	(0.80%)
Reversal of excess deferred income taxes	(2.20%)	(7.80%)
AFUDC - equity	(0.40%)	(0.70%)
Other, net		1.70%
Effective tax rate	17.80%	9.70%
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%	4.80%
Investment tax credits	(6.60%)	(6.40%)
Production tax credits	(0.60%)	(0.80%)
Reversal of excess deferred income taxes	(2.20%)	(8.10%)
AFUDC - equity	(0.70%)	(0.70%)
Other, net	0.30%	0.30%
Effective tax rate	15.70%	10.10%