Commitments and Contingencies (Narrative) (Detail) $ in Millions	1 Months Ended														3 Months Ended				9 Months Ended		12 Months Ended
	Oct. 31, 2020	Sep. 30, 2020 USD ($)	Aug. 31, 2020 USD ($)	Apr. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)		Jul. 31, 2019 USD ($)	May 31, 2019 T	Feb. 28, 2019 USD ($)	Aug. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Apr. 30, 2017 Petition	Aug. 31, 2016 T	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Facility Indicator site gal	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)		Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Impairment of assets and other charges															$ 1,151.0			$ 85.0	$ 1,963.0	$ 1,219.0
Property, plant and equipment, net		$ 56,788.0				$ 57,200.0	[1]								56,788.0				56,788.0		$ 57,200.0	[1]
Nuclear Obligations
Loss Contingencies [Line Items]
Liability protection per nuclear incident available amount																$ 13,800.0	$ 13,900.0
Common Stock
Loss Contingencies [Line Items]
Litigation settlement, benefit fund					$ 320.0
Litigation settlement amount through stock issuance		322.0
DESC Ratepayer Case
Loss Contingencies [Line Items]
Litigation settlement, benefit fund					520.0
SCANA
Loss Contingencies [Line Items]
Reserves for SCANA legal proceedings		228.0				696.0	[1]								228.0				228.0		696.0	[1]
Other expense																			25.0
Other expense, after tax																			25.0
Impairment of assets and other charges															44.0			38.0	44.0	316.0
Impairment of assets and other charges, after tax															33.0			28.0	33.0	236.0
Escrow account					$ 160.0												$ 160.0
Litigation settlement, amount received from SCANA			$ 32.5			192.5
Payment for civil monetary penalty from SCANA				$ 25.0
SCANA | DESC Ratepayer Case
Loss Contingencies [Line Items]
Escrow account																							$ 2,000.0
Credit in future electric rate relief																							2,000.0
Cash payment								$ 117.0															115.0
Proceeds from sale of property		38.5
Property, plant and equipment, net		3.0	$ 27.0												3.0				3.0
SCANA | Other Receivables
Loss Contingencies [Line Items]
Insurance receivables		8.0				111.0									8.0				8.0		111.0
DESC
Loss Contingencies [Line Items]
Contesting amount for filed liens in Fairfield country											$ 285.0
DESC | SCDOR
Loss Contingencies [Line Items]
Proposed assessment amount from audit												$ 410.0
Proportional share of NND project												100.00%
DESC | SOUTH CAROLINA
Loss Contingencies [Line Items]
Amount claimed by plaintiffs in legal matter										$ 100.0
Percentage claimed by plaintiffs in legal matter										100.00%
SCANA and DESC
Loss Contingencies [Line Items]
Disgorgement and prejudgment interest total, amount				$ 112.5
Minimum | SCANA | DESC Ratepayer Case
Loss Contingencies [Line Items]
Proceeds from sale of property																							60.0
Maximum | SCANA | Common Stock
Loss Contingencies [Line Items]
Litigation settlement amount through stock issuance						32.5
Maximum | SCANA | DESC Ratepayer Case
Loss Contingencies [Line Items]
Proceeds from sale of property																							$ 85.0
Virginia Electric and Power Company
Loss Contingencies [Line Items]
Impairment of assets and other charges															200.0			$ 38.0	1,008.0	$ 781.0
Property, plant and equipment, net		$ 32,028.0				$ 32,882.0	[2]								$ 32,028.0				$ 32,028.0		32,882.0	[2]
DESC | NND Project Costs
Loss Contingencies [Line Items]
Percentage ownership in total units		55.00%													55.00%				55.00%
Unfavorable Regulatory Action | VDEQ
Loss Contingencies [Line Items]
Significant emission rate initial carbon cap | T									28,000,000.0
Significant emission rate carbon cap reduction percentage per year									3.00%
Significant emission rate ultimate carbon cap | T									19,600,000
Significant emission rate regional carbon cap | T									27,100,000
Unfavorable Regulatory Action | EPA
Loss Contingencies [Line Items]
Electric generating station facilities heightened entrainment analysis per day | gal																			125,000,000
Carbon Regulations
Loss Contingencies [Line Items]
Significant emission rate per rear CO2 equivalent | T														75,000
CWA | Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Number of mandatory facility-specific factors | Indicator																			5
Number of optional facility-specific factors | Indicator																			6
Number of facilities that are subject to final regulations | Facility																			13
CWA | Unfavorable Regulatory Action | Minimum
Loss Contingencies [Line Items]
Electric generating stations with water withdrawals per day | gal																			2,000,000
CWA | Unfavorable Regulatory Action | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Number of facilities that are subject to final regulations | Facility																			7
CWA | Unfavorable Regulatory Action | EPA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Number of separate petitions for reconsideration granted | Petition													2
CWA | Unfavorable Regulatory Action | EPA | Minimum | Subsequent Event | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Loss contingencies individual circumstances period	2021
CWA | Unfavorable Regulatory Action | EPA | Maximum | Subsequent Event | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Loss contingencies individual circumstances period	2028
Waste Management and Remediation | Unfavorable Regulatory Action | EPA
Loss Contingencies [Line Items]
Number of sites remediation work substantially completed | site																			11
Number of sites with remediation plans | site																			3
Number of sites with an updated work plan | site																			1
Updated work plan, cost increase																			$ 11.0
Number of additional sites which are not under investigation | site																			13
Waste Management and Remediation | Unfavorable Regulatory Action | EPA | Former Gas Plant Site With Post Closure Groundwater Monitoring Program
Loss Contingencies [Line Items]
Environmental remediation reserves																			$ 30.0		30.0
Waste Management and Remediation | Unfavorable Regulatory Action | EPA | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Number of sites with remediation plans | site																			1
Number of additional sites which are not under investigation | site																			2
Waste Management and Remediation | Unfavorable Regulatory Action | EPA | Virginia Electric and Power Company | Former Gas Plant Site With Post Closure Groundwater Monitoring Program
Loss Contingencies [Line Items]
Environmental remediation reserves																			$ 16.0		$ 16.0

[1] Dominion Energy’s Consolidated Balance Sheet at December 31, 2019 has been derived from the audited Consolidated Balance Sheet at that date.

[2] Virginia Power’s Consolidated Balance Sheet at December 31, 2019 has been derived from the audited Consolidated Balance Sheet at that date.