Income Taxes (Reconciliation of Income Taxes at the U.S. Statutory Federal Income Tax Rate) (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Computation [Line Items]
U.S. statutory rate	21.00%	21.00%	21.00%	35.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	2.00%	1.50%	4.30%
Investment tax credits	(9.60%)	(11.40%)	(2.30%)
Production tax credits	(0.70%)	(2.10%)	(0.80%)
Valuation allowances	0.90%	0.50%	0.40%
Reversal of excess deferred income taxes	(5.40%)	(3.20%)	(2.30%)
Federal legislative change	0.00%	0.00%	1.80%
State legislative change	0.00%	0.00%	(0.80%)
Write-off of regulatory assets	0.00%	21.70%	0.00%
Change in tax status	(1.70%)	(5.50%)	0.00%
AFUDC—equity	(0.20%)	(0.20%)	(0.30%)
Changes in state deferred taxes associated with assets held for sale	(3.20%)	0.00%	0.00%
Absence of tax on noncontrolling interest	3.80%	(0.20%)	(0.10%)
Employee stock ownership plan deduction	(0.90%)	(1.40%)	(0.50%)
Nondeductible goodwill	0.00%	1.80%	0.00%
Other, net	(0.10%)	1.50%	(0.40%)
Effective tax rate	5.90%	24.00%	20.00%
Virginia Electric and Power Company
Effective Income Tax Computation [Line Items]
U.S. statutory rate	21.00%	21.00%	21.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	4.80%	4.50%	4.70%
Investment tax credits	(4.50%)	(2.90%)	(3.50%)
Production tax credits	(0.70%)	(0.70%)	(0.70%)
Valuation allowances	0.00%	0.00%	0.00%
Reversal of excess deferred income taxes	(2.20%)	(3.10%)	(3.20%)
Federal legislative change	0.00%	0.00%	1.30%
State legislative change	0.00%	0.00%	0.00%
Write-off of regulatory assets	0.00%	0.00%	0.00%
Change in tax status	0.00%	0.00%	0.00%
AFUDC—equity	0.00%	0.00%	(0.50%)
Changes in state deferred taxes associated with assets held for sale		0.00%	0.00%
Absence of tax on noncontrolling interest	0.00%	0.00%	0.00%
Employee stock ownership plan deduction	0.00%	0.00%
Nondeductible goodwill	0.00%	0.00%	0.00%
Other, net	(0.10%)	(0.20%)	(0.10%)
Effective tax rate	18.30%	18.60%	19.00%