Commitments and Contingencies (Narrative) (Detail) shares in Millions, $ in Millions	1 Months Ended																3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2021 shares	Jul. 31, 2021 USD ($) shares	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)		Oct. 31, 2020	Sep. 30, 2020 USD ($)	Aug. 31, 2020 USD ($)	Jul. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)	Aug. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Aug. 31, 2017 USD ($)	Apr. 30, 2017 Petition	Aug. 31, 2016 T	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Indicator Facility site gal	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)		Dec. 31, 2018 USD ($)	Mar. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Impairment of assets and other charges																	$ (222.0)	$ 1,151.0	$ 194.0	$ 1,963.0
Property, plant and equipment, net				$ 57,848.0	[1]												58,386.0		58,386.0		$ 57,848.0	[1]
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]
Other expense																				25.0
Other expense, after tax																				25.0
Impairment of assets and other charges																		44.0	100.0	44.0
Impairment of assets and other charges, after tax																		33.0	75.0	33.0
Escrow account																								$ 160.0
Litigation settlement expense								$ 32.5		$ 192.5
Litigation settlement paid				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 | State Court Derivative Case
Loss Contingencies [Line Items]
Litigation settlement paid			$ 33.0
SCANA | Federal Court Merger Case
Loss Contingencies [Line Items]
Litigation settlement paid			63.0
SCANA | Other Current Liabilities
Loss Contingencies [Line Items]
Reserves for SCANA legal proceedings				208.0													196.0		196.0		208.0
SCANA | Other Receivables
Loss Contingencies [Line Items]
Insurance receivables				8.0													41.0		41.0		8.0
DESC
Loss Contingencies [Line Items]
Litigation settlement expense		$ 99.0
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																	(230.0)	$ 200.0	(269.0)	$ 1,008.0
Property, plant and equipment, net				32,569.0	[2]												$ 33,876.0		$ 33,876.0		32,569.0	[2]
Virginia Electric and Power Company | EPA and State Regulatory Agencies
Loss Contingencies [Line Items]
Number of facilities to assess the applicability of section 316(b) | Facility																			3
Hydroelectric Facilities | EPA and State Regulatory Agencies
Loss Contingencies [Line Items]
Number of facilities to assess the applicability of section 316(b) | Facility																			8
Dominion Energy South Carolina Inc | NND Project
Loss Contingencies [Line Items]
Noncontrolling partnership interest																	55.00%		55.00%
Contesting amount for filed liens in Fairfield country												$ 285.0
Dominion Energy South Carolina Inc | SCDOR
Loss Contingencies [Line Items]
Litigation settlement paid				$ 165.0
Proposed assessment amount from audit													$ 410.0
Proportional share of NND project													100.00%
Dominion Energy South Carolina Inc | SOUTH CAROLINA
Loss Contingencies [Line Items]
Amount claimed by plaintiffs in legal matter														$ 100.0
Percentage claimed by plaintiffs in legal matter														100.00%
Dominion Energy South Carolina Inc | DESC | Common Stock
Loss Contingencies [Line Items]
Litigation settlement through stock issuance | shares		1.4
Dominion Energy South Carolina Inc | DESC | Common Stock | SCDOR
Loss Contingencies [Line Items]
Initial litigation settlement through stock issuance | shares	0.6
Dominion Energy South Carolina Inc | Minimum | SCDOR
Loss Contingencies [Line Items]
Initial litigation settlement amount through stock issuance			$ 43.0
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]
Public Utilities Significant Emission Rate Per Year 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																			15
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 | 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 | 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 | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Loss contingencies individual circumstances period						2028
CWA | Unfavorable Regulatory Action | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Number of facilities that are subject to final regulations | Facility																			9
Waste Management and Remediation | Unfavorable Regulatory Action | EPA
Loss Contingencies [Line Items]
Number of sites remediation work substantially completed | site																			12
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																			12
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																			$ 40.0		42.0
Waste Management and Remediation | Unfavorable Regulatory Action | Virginia Electric and Power Company | EPA
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 | Virginia Electric and Power Company | EPA | Former Gas Plant Site With Post Closure Groundwater Monitoring Program
Loss Contingencies [Line Items]
Environmental remediation reserves																			$ 25.0		$ 26.0

[1] Dominion Energy’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.

[2] Virginia Power’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.