Commitments and Contingencies (Narrative) (Detail)			1 Months Ended							3 Months Ended
	Apr. 30, 2015 Facility	Oct. 31, 2014 MGD Facility	Apr. 30, 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, 2020 USD ($) Product	Mar. 31, 2019 USD ($)	Dec. 31, 2019 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 DESC hydroelectric facilities subject to regulations | Facility		5
Number of manufacturing gas plant decommissioned sites that contain residues of byproduct chemicals | Product										4
Estimated environmental remediation activities at manufacturing gas plant sites										$ 10,000,000
Estimated increase in remediation costs for Congaree River site										8,000,000
Environmental remediation costs recognized in regulatory assets										23,000,000
Number of CCR landfills facilities subject to final rule | Facility	3
Impairment of assets and other charges										2,000,000	$ 262,000,000
Customer refundable fees, alternative plan										3,432,000,000		$ 3,466,000,000
Transmission assets related to BLRA capital costs										345,000,000
Transmission assets related to BLRA regulatory assets										43,000,000
Reserves for litigation and regulatory proceedings										492,000,000		492,000,000
Insurance receivables										6,000,000		$ 6,000,000
Settlement payable by all										520,000,000
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
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%
Nuclear Insurance
Loss Contingencies [Line Items]
Maximum liability each nuclear plant is insured against										$ 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
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
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
Maximum [Member] | Nuclear Insurance
Loss Contingencies [Line Items]
Maximum liability protection per nuclear incident amount										14,000,000,000.0
Amount that could be assessed for each licensed reactor										138,000,000
Amount that could be assessed for each licensed reactor per year										21,000,000
Dominion Energy South Carolina, Inc.
Loss Contingencies [Line Items]
Reduction of liens filed										33,000,000
SCANA | Subsequent Event
Loss Contingencies [Line Items]
Payment of civil monetary penalty			$ 25,000,000
SCANA and DESC | Subsequent Event
Loss Contingencies [Line Items]
Payment of disgorgement and prejudgment interest			$ 112,500,000
DESC Summer | Maximum [Member] | Nuclear Insurance
Loss Contingencies [Line Items]
Amount that could be assessed for each licensed reactor										92,000,000
Amount that could be assessed for each licensed reactor per year										$ 14,000,000
DESC Ratepayer Case
Loss Contingencies [Line Items]
Impairment of assets and other charges											105,000,000
Impairment of assets and other charges, after-tax											79,000,000
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
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
Escrow amount							$ 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					$ 42,000,000
DESC Ratepayer Case | Minimum [Member]
Loss Contingencies [Line Items]
Estimated aggregate fair value of certain real estate							60,000,000
DESC Ratepayer Case | Maximum [Member]
Loss Contingencies [Line Items]
Estimated aggregate fair value of certain real estate							$ 85,000,000
DESC Ratepayer Case | Dominion Energy South Carolina, Inc. | Impairment of Assets and Other Charges
Loss Contingencies [Line Items]
Impairment of assets and other charges											166,000,000
Impairment of assets and other charges, after-tax											$ 125,000,000
Wrongful Death Suit of Estate of Jose Larios | Dominion Energy South Carolina, Inc.
Loss Contingencies [Line Items]
Litigation settlement expense awarded				$ 19,000,000
Carbon Regulations [Member]
Loss Contingencies [Line Items]
Significant emission rate per year CO2 equivalent | T									75,000