Income Taxes (Schedule of Deductible Loss and Credit Carryforwards) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Deductible loss and credit carryforwards [Line Items]
Deductible amount	$ 4,830
Losses, Deferred tax asset	1,561
Losses, Valuation allowance	(155)
Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Losses, Deferred tax asset	354
Losses, Valuation allowance	(6)
Federal
Deductible loss and credit carryforwards [Line Items]
Deductible amount	1,169
Losses, Deferred tax asset	$ 246
Losses, Expiration Period	2037
Federal | Investment Credits
Deductible loss and credit carryforwards [Line Items]
Tax credits, Deferred tax asset	$ 736
Federal | Investment Credits | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax credits, Deferred tax asset	$ 294
Federal | Investment Credits | Earliest Tax Year
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2036
Federal | Investment Credits | Earliest Tax Year | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2036
Federal | Investment Credits | Latest Tax Year
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2040
Federal | Investment Credits | Latest Tax Year | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2040
Federal | Federal production credits
Deductible loss and credit carryforwards [Line Items]
Tax credits, Deferred tax asset	$ 86
Federal | Federal production credits | Earliest Tax Year
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2036
Federal | Federal production credits | Latest Tax Year
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2040
Federal | Federal Production And Other Credits
Deductible loss and credit carryforwards [Line Items]
Tax credits, Deferred tax asset	$ 14
Federal | Federal Production And Other Credits | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax credits, Deferred tax asset	$ 51
Federal | Federal Production And Other Credits | Earliest Tax Year
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2036
Federal | Federal Production And Other Credits | Earliest Tax Year | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2036
Federal | Federal Production And Other Credits | Latest Tax Year
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2039
Federal | Federal Production And Other Credits | Latest Tax Year | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2040
State
Deductible loss and credit carryforwards [Line Items]
Deductible amount	$ 3,661
Losses, Deferred tax asset	198
Losses, Valuation allowance	(61)
State minimum tax credits	$ 139
State | Earliest Tax Year
Deductible loss and credit carryforwards [Line Items]
Losses, Expiration Period	2020
State | Latest Tax Year
Deductible loss and credit carryforwards [Line Items]
Losses, Expiration Period	2040
State | Investment Credits | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Losses, Valuation allowance	$ (6)
Tax credits, Deferred tax asset	$ 9
Tax Credits, Expiration Period	2024
State | Investment And Other Credit
Deductible loss and credit carryforwards [Line Items]
Losses, Valuation allowance	$ (94)
Tax credits, Deferred tax asset	$ 142
State | Investment And Other Credit | Earliest Tax Year
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2020
State | Investment And Other Credit | Latest Tax Year
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2031