Commitments and Contingencies (Narrative) (Detail) gal in Millions, MMcf in Millions, $ in Millions		1 Months Ended										3 Months Ended		12 Months Ended
	Feb. 01, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jul. 31, 2019 USD ($)	May 31, 2019 USD ($) T	Mar. 31, 2019 USD ($) MMcf	Feb. 28, 2019 USD ($)	Jan. 31, 2019 USD ($)	Aug. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Aug. 31, 2016 T	Apr. 30, 2015 Facility	Mar. 31, 2019 USD ($) MMcf	Jun. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) Facility gal		Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
ARO incurred														$ 2,413.0	[1]	$ 20.0
Regulatory liability														11,498.0		7,196.0
Impairment of assets and other charges														1,535.0		403.0	$ 15.0
Property, Plant and Equipment, Net														$ 69,082.0		54,560.0
DESC
Loss Contingencies [Line Items]
Contesting amount for filed liens in Fairfield country								$ 285.0
DESC | NND Project costs
Loss Contingencies [Line Items]
Equity method investment, ownership percentage														55.00%
SCDOR | DESC
Loss Contingencies [Line Items]
Proposed assessment amount from audit									$ 410.0
Proportionate Share of NND Project									100.00%
SOUTH CAROLINA | DESC
Loss Contingencies [Line Items]
Amount claimed by plaintiffs in legal matter						$ 100.0
Percentage claimed by plaintiffs in legal matter						100.00%
DESC Ratepayer Case
Loss Contingencies [Line Items]
Litigation settlement paid	$ 520.0
Virginia Electric and Power Company
Loss Contingencies [Line Items]
ARO incurred														$ 2,408.0	[1]	14.0
Regulatory liability														5,241.0		4,946.0
Asset Impairment Charges After Tax							$ 119.0
Impairment of assets and other charges							$ 160.0							757.0
Property, Plant and Equipment, Net														32,882.0		$ 30,521.0
Litigation settlement paid				$ 7.0
Virginia Electric and Power Company | Future Ash Pond and Landfill Closure Costs
Loss Contingencies [Line Items]
ARO incurred												$ 202.0
Virginia Electric and Power Company | Increase In Property Plant And Equipment
Loss Contingencies [Line Items]
ARO incurred												1,300.0	$ 46.0
Virginia Electric and Power Company | Increase in Regulatory Assets
Loss Contingencies [Line Items]
ARO incurred													4.0
Virginia Electric and Power Company | Cost of Landfills and Beneficial Reuse
Loss Contingencies [Line Items]
ARO incurred												2,400.0	131.0
Virginia Electric and Power Company | Other operations and maintenance
Loss Contingencies [Line Items]
ARO incurred												113.0	81.0
ARO incurred, after tax												$ 84.0	$ 60.0
Virginia Electric and Power Company | Impairment Of Assets And Other Charges [Member]
Loss Contingencies [Line Items]
Asset Impairment Charges After Tax		$ 12.0		46.0	$ 257.0
Impairment of assets and other charges		$ 17.0		$ 62.0	346.0
Virginia Electric and Power Company | Minimum
Loss Contingencies [Line Items]
Proposed revenue requirement					$ 225.0
SCANA
Loss Contingencies [Line Items]
Reserves														696.0
SCANA | DESC Ratepayer Case
Loss Contingencies [Line Items]
Credit in future electric rate relief														2.0
Escrow account														2.0
Cash payment			$ 117.0											115.0
Property, Plant and Equipment, Net			$ 54.0
SCANA | Other Receivables [Member]
Loss Contingencies [Line Items]
Insurance receivables														111.0
SCANA | Impairment Of Assets And Other Charges [Member]
Loss Contingencies [Line Items]
Asset Impairment Charges After Tax														480.0
Impairment of assets and other charges														641.0
SCANA | Minimum | DESC Ratepayer Case
Loss Contingencies [Line Items]
Proceeds from sale of property														60.0
SCANA | Maximum | DESC Ratepayer Case
Loss Contingencies [Line Items]
Proceeds from sale of property														$ 85.0
CWA | EPA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Compliance date														2023-12
CWA | EPA | 2015 Effluent Limitations Guidelines Rule for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Compliance date														2020-11
CCR | Virginia Electric and Power Company | Minimum
Loss Contingencies [Line Items]
Cubic yards of CCR required by legislation to be beneficially reused | MMcf					6.8							6.8
Carbon Regulations
Loss Contingencies [Line Items]
Significant emission rate per rear CO2 equivalent | T										75,000
Unfavorable Regulatory Action | EPA
Loss Contingencies [Line Items]
Electric generating station facilities heightened entrainment analysis per day | gal														125
Unfavorable Regulatory Action | VDEQ
Loss Contingencies [Line Items]
Significant emission rate initial carbon cap | T				28.0
Significant emission rate ultimate carbon cap | T				19.6
Unfavorable Regulatory Action | CWA
Loss Contingencies [Line Items]
Number of facilities that may be subject to final regulations | Facility														13
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Former Gas Plant Site with Post Closure Groundwater Monitoring Program
Loss Contingencies [Line Items]
Environmental remediation reserves														$ 34.0
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | 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
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Virginia Electric and Power Company | Former Gas Plant Site with Post Closure Groundwater Monitoring Program | Other operations and maintenance
Loss Contingencies [Line Items]
Environmental Remediation Expense									$ 16.0
Environmental Remediation Expense, net of tax									$ 12.0
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | SCANA
Loss Contingencies [Line Items]
Updated remediation work plan, cost increase														$ 8.0
Unfavorable Regulatory Action | CCR | Facilities Subject to Coal Combustion Residual Final Rule | Environmental Protection Agency Final Rule Regulating Management of CCRs
Loss Contingencies [Line Items]
Number of facilities with CCR | Facility											11
U S department of treasury [member] | FERC-regulated | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Regulatory liability				$ 7.0

[1] Reflects future ash pond and landfill closure costs at certain utility generation facilities. See Note 23 for further information.