Commitments and Contingencies (Narrative) (Detail)			1 Months Ended										3 Months Ended			12 Months Ended
	Apr. 30, 2015 Facility	Oct. 31, 2014 MGD Facility	Dec. 31, 2020 USD ($)	Oct. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Aug. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jul. 31, 2019 USD ($)	Feb. 28, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Aug. 31, 2016 T	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2020 USD ($) Product	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Electric generating stations with water withdrawals under CWA | MGD		125
Electric generating stations with water withdrawals with heightened entrainment analysis under CWA | MGD		2
Number of DESC facilities subject to final regulations | Facility		5
Number of MGP decommissioned sites that contain residues of byproduct chemicals | Product																4
Estimated environmental remediation activities at MGP sites																$ 10,000,000
Estimated increase in remediation costs for Congaree River site																11,000,000
Environmental remediation costs recognized in regulatory assets			$ 22,000,000													22,000,000
Number of CCR landfills facilities subject to final rule | Facility	3
Impairment loss, NND Project														$ 1,400,000,000	$ 4,000,000				$ 1,100,000,000
Impairment loss, NND Project, after-tax														870,000,000	$ 3,000,000				$ 690,000,000
Maximum amount of capital cost recovery related to the NND Project														2,800,000,000
Impairment of assets and other charges													$ 105,000,000			(14,000,000)	$ 576,000,000	$ 1,376,000,000
Impairment of assets and other charges, after-tax													79,000,000
Customer refundable fees, alternative plan			3,288,000,000													3,288,000,000	3,466,000,000
Regulatory liability for refunds to natural gas customers													2,000,000
Regulatory liability for refunds to natural gas customers, after tax													2,000,000
Regulatory asset impairment charges committed to forgo recovery													264,000,000
Tax charge related to regulatory assets committed to forgo recovery													198,000,000
Transmission assets related to BLRA capital costs			309,000,000													309,000,000
Transmission assets related to BLRA regulatory assets			63,000,000													63,000,000
Reserves for litigation and regulatory proceedings			208,000,000													208,000,000	492,000,000
Insurance receivables			8,000,000													8,000,000	6,000,000
Proposed settlement payable by all																				$ 520,000,000
Proposed settlement payable by company									$ 100,000,000											$ 320,000,000
Proportionate ownership share in project									100.00%		100.00%
Proposed assessment amount from SCDOR audit											$ 410,000,000
Agreement in principle to resolve the SCDOR matter			165,000,000
Contesting amount for filed liens in Fairfield country																285,000,000
Reduction of liens filed																$ 60,000,000
Percentage share of reduction of liens filed																55.00%
Energy payments under power purchase contracts			64,000,000							$ 24,000,000				24,000,000		$ 64,000,000	37,000,000	24,000,000
Summer
Loss Contingencies [Line Items]
Proceeds from legal settlements of share of claims incurred in previous year																4,000,000	3,000,000
Nuclear Insurance
Loss Contingencies [Line Items]
Maximum liability each nuclear plant is insured against			450,000,000													$ 450,000,000
Inflation adjustment period for nuclear insurance																5 years
NEIL maximum insurance coverage to nuclear facility for property damage and outage costs			2,750,000,000													$ 2,750,000,000
NEIL maximum insurance coverage to nuclear facility for property damage and outage costs from non-nuclear event																2,330,000,000
NEIL aggregate maximum loss for any single loss occurrence			$ 2,750,000,000													2,750,000,000
NEIL maximum retrospective premium assessment																24,000,000
EMANI maximum insurance coverage for Summer station unit 1 for property damage and outage costs from non-nuclear event																415,000,000
EMANI maximum retrospective premium assessment																2,000,000
Common Stock | Dominion Energy
Loss Contingencies [Line Items]
Common stock issued to satisfy the settlement					$ 322,000,000
Dominion Energy South Carolina, Inc.
Loss Contingencies [Line Items]
Reduction of liens filed																33,000,000
SCANA
Loss Contingencies [Line Items]
Payment of civil monetary penalty																25,000,000
SCANA and DESC
Loss Contingencies [Line Items]
Payment of disgorgement and prejudgment interest																112,500,000
Impairment of Assets and Other Charges | Dominion Energy South Carolina, Inc.
Loss Contingencies [Line Items]
Impairment of assets and other charges																97,000,000	590,000,000
Impairment of assets and other charges, after-tax																73,000,000	$ 444,000,000
SCANA Combination
Loss Contingencies [Line Items]
Regulatory asset impairment charges committed to forgo recovery													258,000,000
Tax charge related to regulatory assets committed to forgo recovery													194,000,000
DESC Ratepayer Case
Loss Contingencies [Line Items]
Customer refundable fees, alternative plan													1,000,000,000.0
Customer refund fees alternative plan after tax													$ 756,000,000
Customer refunded estimated period													11 years
Previous existing regulatory liability													$ 1,000,000,000.0
Previous existing regulatory liability, years													20 years
Escrow amount										2,000,000,000.0				$ 2,000,000,000.0				$ 2,000,000,000.0
Credit in future electric rate relief for ratepayer case										2,000,000,000.0
Cash payment related to Ratepayer Case								$ 117,000,000		115,000,000
Property with net value transferred						$ 22,000,000
Property with net value transferred, cash contribution				$ 38,500,000
Conveyance of property with net recorded value				$ 3,000,000
DESC Ratepayer Case | Common Stock | Dominion Energy
Loss Contingencies [Line Items]
Common stock issued to satisfy the settlement																$ 322,000,000
Wrongful Death Suit of Estate of Jose Larios | Dominion Energy South Carolina, Inc.
Loss Contingencies [Line Items]
Agreement in principle to resolve the SCDOR matter							$ 19,000,000
NND Project
Loss Contingencies [Line Items]
Jointly owned utility plant, proportionate ownership share			55.00%													55.00%
Maximum [Member] | Nuclear Insurance
Loss Contingencies [Line Items]
Maximum liability protection per nuclear incident amount																$ 13,800,000,000
Amount that could be assessed for each licensed reactor			$ 138,000,000													138,000,000
Amount that could be assessed for each licensed reactor per year																21,000,000
Maximum [Member] | DESC Summer | Nuclear Insurance
Loss Contingencies [Line Items]
Amount that could be assessed for each licensed reactor			$ 92,000,000													92,000,000
Amount that could be assessed for each licensed reactor per year																$ 14,000,000
Maximum [Member] | DESC Ratepayer Case
Loss Contingencies [Line Items]
Estimated aggregate fair value of certain real estate										85,000,000
Minimum [Member] | DESC Ratepayer Case
Loss Contingencies [Line Items]
Estimated aggregate fair value of certain real estate										$ 60,000,000
Carbon Regulations [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Significant emission rate per year CO2 equivalent | T												75,000