Income Taxes (Reconciliation of Income Taxes at the U.S. Statutory Federal Income Tax Rate) (Detail)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 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	2.00%	1.50%
Investment tax credits	(5.60%)	(30.50%)
Production tax credits	(0.50%)	(2.40%)
Reversal of excess deferred income taxes	(3.80%)	(14.50%)
State legislative change	(1.00%)
Change in tax status		(6.10%)
AFUDC - equity	(0.50%)	(1.10%)
Changes in state deferred taxes associated with assets held for sale	(0.50%)	(11.60%)
Absence of tax on noncontrolling interest	(0.20%)	14.10%
Other, net	(1.10%)	(1.80%)
Effective tax rate	9.80%	(31.40%)
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%	4.70%
Investment tax credits	(5.80%)	(5.60%)
Production tax credits	(0.60%)	(0.90%)
Reversal of excess deferred income taxes	(2.20%)	(1.90%)
State legislative change	(1.00%)
AFUDC - equity	(0.50%)	(0.30%)
Effective tax rate	15.40%	17.00%