Commitments and Contingencies (Narrative) (Detail)			1 Months Ended						3 Months Ended			12 Months Ended
	Apr. 30, 2015 Facility	Oct. 31, 2014 MGD Facility	Sep. 30, 2019 USD ($)	Jul. 31, 2019 USD ($)	Feb. 28, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Aug. 31, 2016 T	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) Product	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Feb. 28, 2020 USD ($)
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 MGP decommissioned sites that contain residues of byproduct chemicals | Product												4
Estimated environmental remediation activities at MGP 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 loss, NND Project										$ 1,400,000,000	$ 4,000,000			$ 1,100,000,000
Impairment loss, NND Project, after-tax										870,000,000	$ 3,000,000			690,000,000
Maximum amount of capital cost recovery related to the NND Project										2,800,000,000
Impairment of assets and other charges									$ 105,000,000			576,000,000	$ 1,376,000,000	$ 1,118,000,000
Impairment of assets and other charges, after-tax									79,000,000
Customer refundable fees, alternative plan						$ 2,390,000,000				2,390,000,000		3,466,000,000	2,390,000,000
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
Transmission assets related to BLRA capital costs												345,000,000
Transmission assets related to BLRA regulatory assets												37,000,000
Reserves for litigation and regulatory proceedings						11,000,000				11,000,000		492,000,000	11,000,000
Insurance receivables												6,000,000
Escrow amount						115,000,000				115,000,000			115,000,000
Proposed settlement payable by company					$ 100,000,000
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%
Energy payments under power purchase contracts						24,000,000				24,000,000		$ 37,000,000	24,000,000
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
Subsequent Event
Loss Contingencies [Line Items]
Proposed settlement payable by all															$ 520,000,000
Proposed settlement payable by company															$ 320,000,000
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
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
Impairment of Assets and Other Charges | Dominion Energy South Carolina, Inc.
Loss Contingencies [Line Items]
Impairment of assets and other charges												590,000,000
Impairment of assets and other charges, after-tax												$ 444,000,000
SCANA Combination
Loss Contingencies [Line Items]
Regulatory asset impairment charges committed to forgo recovery									258,000,000
Tax charge related to regulatory assets committed to forgo recovery									194,000,000
DESC Ratepayer Case
Loss Contingencies [Line Items]
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
Escrow amount						2,000,000,000.0				$ 2,000,000,000.0			$ 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
Wrongful Death Suit of Estate of Jose Larios | Dominion Energy South Carolina, Inc.
Loss Contingencies [Line Items]
Litigation settlement expense awarded			$ 19,000,000
NND Project
Loss Contingencies [Line Items]
Jointly owned utility plant, proportionate ownership share												55.00%
Carbon Regulations [Member]
Loss Contingencies [Line Items]
Significant emission rate per year CO2 equivalent | T								75,000