Income Taxes (Reconciliation of Income Taxes at the U.S. Statutory Federal Income Tax Rate) (Detail)	6 Months Ended
	Jun. 30, 2021	Jun. 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	2.30%	4.10%
Investment tax credits	(5.30%)	(19.50%)
Production tax credits	(0.40%)	(1.60%)
Reversal of excess deferred income taxes	(3.50%)	(6.50%)
State legislative change	(1.50%)
AFUDC - equity	(0.50%)	(2.10%)
Other, net	(0.40%)	1.20%
Effective tax rate	11.70%	(3.40%)
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%	4.90%
Investment tax credits	(5.80%)	(11.30%)
Production tax credits	(0.60%)	(2.00%)
Reversal of excess deferred income taxes	(2.10%)	(0.80%)
State legislative change	(1.70%)
AFUDC - equity	(0.60%)	(0.60%)
Other, net	0.30%	1.10%
Effective tax rate	15.00%	12.30%