Commitments and Contingencies (Nuclear Operations) (Narrative) (Detail) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Maximum liability protection per nuclear incident in summer per year			$ 14,000,000
NRC minimum requirement for nuclear power plant licensees			1,060,000,000.00
Maximum assessment for premiums on insurance policy			31,000,000
Maximum assessment for insurance policy			81,000,000
Spent Nuclear Fuel
Loss Contingencies [Line Items]
Receivables			52,000,000	$ 49,000,000
Maximum
Loss Contingencies [Line Items]
Amount that could be assessed for each licensed reactor			138,000,000
Amount that could be assessed for each licensed reactor per reactor			21,000,000
Nuclear Obligations
Loss Contingencies [Line Items]
Maximum liability protection per nuclear incident amount		$ 14,100,000,000	13,900,000,000
Virginia Electric and Power Company
Loss Contingencies [Line Items]
Maximum assessment for premiums on insurance policy			50,000,000
Maximum assessment for insurance policy			10,000,000
Virginia Electric and Power Company | Spent Nuclear Fuel
Loss Contingencies [Line Items]
Receivables			35,000,000	30,000,000
DESC
Loss Contingencies [Line Items]
Maximum liability protection per nuclear incident amount			138,000,000
Minimum Liability Protection Per Nuclear Incident Amount			21,000,000
Maximum liability protection per nuclear incident in summer			92,000,000
Public liability claims			14,000,000.0
Maximum of Claim Liability Insured			450,000,000
DESC | NEIL
Loss Contingencies [Line Items]
Maximum loss for any single loss occurrence			2,750,000,000
Annual Premium			24,000,000
DESC | Nuclear Obligations | NEIL
Loss Contingencies [Line Items]
Property insurance coverage			2,750,000,000
DESC | Non-nuclear Obligation | NEIL
Loss Contingencies [Line Items]
Property insurance coverage			2,330,000,000
DESC | Non-nuclear Obligation | European Mutual Association
Loss Contingencies [Line Items]
Property insurance coverage			415,000,000
Annual Premium			2,000,000
Surry and North Anna
Loss Contingencies [Line Items]
Settlement amount			15,000,000	16,000,000	$ 22,000,000
Millstone
Loss Contingencies [Line Items]
Settlement amount			11,000,000	$ 13,000,000	$ 14,000,000
Millstone | Dominion Energy and Virginia Electric and Power
Loss Contingencies [Line Items]
Amount of coverage purchased from commercial insurance pools			450,000,000
Millstone Unit 1
Loss Contingencies [Line Items]
Minimum financial assurance			2,800,000,000
Kewaunee
Loss Contingencies [Line Items]
Maximum assessment for premiums on insurance policy	$ 50,000,000
Kewaunee | Nuclear Obligations
Loss Contingencies [Line Items]
Maximum liability protection per nuclear incident amount			100,000,000
Kewaunee | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Minimum financial assurance			1,800,000,000
Summer Unit
Loss Contingencies [Line Items]
Settlement amount			$ 3,000,000