Income Taxes (Schedule of Deductible Loss and Credit Carryforwards) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Deductible loss and credit carryforwards [Line Items]
Deductible amount	$ 4,435
Losses, Deferred tax asset	1,856
Losses, Valuation allowance	(155)
Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Deferred Tax Asset	280
Valuation Allowance	(5)
Federal
Deductible loss and credit carryforwards [Line Items]
Deductible amount	1,361
Losses, Deferred tax asset	$ 286
Losses, Expiration Period	2037
Tax credits, Deferred tax asset	$ 40
Federal | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Deferred Tax Asset	213
Federal | Investment Credits
Deductible loss and credit carryforwards [Line Items]
Tax credits, Deferred tax asset	922
Federal | Federal production credits
Deductible loss and credit carryforwards [Line Items]
Tax credits, Deferred tax asset	126
Federal | Federal Production And Other Credits | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Deferred Tax Asset	58
State
Deductible loss and credit carryforwards [Line Items]
Deductible amount	3,074
Losses, Deferred tax asset	173
Losses, Valuation allowance	(57)
State minimum tax credits	165
State | Investment Credits | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Deferred Tax Asset	9
Tax Credits, Valuation allowance	$ (5)
Tax Credits, Expiration Period	2024
State | Investment and Other Credit
Deductible loss and credit carryforwards [Line Items]
Tax credits, Deferred tax asset	$ 144
Tax Credits, Valuation allowance	$ (98)
Earliest Tax Year | Federal | Investment Credits
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2035
Earliest Tax Year | Federal | Investment Credits | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2035
Earliest Tax Year | Federal | Federal production credits
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2035
Earliest Tax Year | Federal | Federal Production And Other Credits
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2035
Earliest Tax Year | Federal | Federal Production And Other Credits | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2035
Earliest Tax Year | State
Deductible loss and credit carryforwards [Line Items]
Losses, Expiration Period	2020
Earliest Tax Year | State | Investment and Other Credit
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2020
Latest Tax Year | Federal | Investment Credits
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2039
Latest Tax Year | Federal | Investment Credits | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2039
Latest Tax Year | Federal | Federal production credits
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2039
Latest Tax Year | Federal | Federal Production And Other Credits
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2038
Latest Tax Year | Federal | Federal Production And Other Credits | Virginia Electric and Power Company
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2039
Latest Tax Year | State
Deductible loss and credit carryforwards [Line Items]
Losses, Expiration Period	2038
Latest Tax Year | State | Investment and Other Credit
Deductible loss and credit carryforwards [Line Items]
Tax Credits, Expiration Period	2031