Commitments and Contingencies (Narrative) (Detail) $ in Millions	1 Months Ended														12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Aug. 31, 2020 USD ($)	Jun. 30, 2020 T	Apr. 30, 2020 USD ($)	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	Dec. 31, 2020 USD ($) Facility Indicator site gal	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Impairment of assets and other charges															$ 2,105.0	$ 1,520.0	$ 12.0
Property, plant and equipment, net	$ 57,848.0						$ 57,200.0								57,848.0	57,200.0
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	208.0						696.0								208.0	696.0
Other expense															25.0
Other expense, after tax															25.0
Escrow account						$ 160.0
Litigation settlement, amount received from SCANA			$ 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
SCANA | Corporate and Other
Loss Contingencies [Line Items]
Impairment of assets and other charges															90.0	641.0
Impairment of assets and other charges, after tax															68.0	480.0
SCANA | Other Receivables
Loss Contingencies [Line Items]
Insurance receivables	8.0						111.0								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%
Litigation settlement paid	165.0
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 awarded to other party					$ 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															1,093.0	757.0
Property, plant and equipment, net	$ 32,569.0						$ 32,882.0								$ 32,569.0	32,882.0
DESC | NND Project Costs
Loss Contingencies [Line Items]
Percentage ownership in total units	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]
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 | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Number of facilities that are subject to final regulations | Facility															9
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
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
Environmental remediation expense															$ 14.0		16.0
Environmental remediation expense net of tax															$ 11.0		12.0
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															$ 42.0	34.0
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
Environmental remediation expense															$ 10.0		16.0
Environmental remediation expense net of tax															$ 7.0		$ 12.0
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															$ 26.0	$ 16.0