Commitments and Contingencies (Narrative) (Detail) shares in Millions		1 Months Ended														3 Months Ended		6 Months Ended
	Oct. 31, 2014 MGD Facility	Jul. 31, 2023 USD ($)	Jun. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	May 31, 2022 shares	Aug. 31, 2021 shares	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Oct. 31, 2020	Nov. 30, 2019 gal	Jun. 30, 2018 USD ($)	Sep. 30, 2017 Petition	Apr. 30, 2017 Petition	Aug. 31, 2016 T	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Jun. 30, 2023 USD ($) Indicator Product Facility	Dec. 31, 2022 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
Measurement of groundwater withdrawals | gal											3,000,000
Number of manufacturing gas plant decommissioned sites that contain residues of byproduct chemicals | Product																		4
Estimated environmental remediation activities at manufacturing gas plant sites																		$ 20,000,000
Environmental remediation costs recognized in regulatory assets			$ 38,000,000													$ 38,000,000		$ 38,000,000
Number of facilities inactive subject to final rule | Facility																		3
Reserves for litigation and regulatory proceedings			66,000,000													66,000,000		$ 66,000,000	$ 94,000,000
Insurance receivables			72,000,000													72,000,000		72,000,000	68,000,000
Proportionate ownership share in project												100.00%
Proposed assessment amount from SCDOR audit												$ 410,000,000
Litigation settlement expense awarded									$ 165,000,000
Real estate transfer to satisfy obligation under settlement					$ 51,000,000
SCDOR
Loss Contingencies [Line Items]
Fair value of certain additional utility property transferred																			3,000,000
Fair value of certain remaining utility property transferred			11,000,000
Fair value of certain non-utility property transferred				$ 28,000,000
Fair value of certain utility property transferred																	$ 10,000,000
Gain from transferred utility property																		9,000,000
Gain from transferred utility property, after tax																		7,000,000
Gain from transferred remaining utility property																11,000,000		11,000,000
Gain from transferred remaining utility property, after tax																8,000,000		$ 8,000,000
Common Stock | Dominion Energy
Loss Contingencies [Line Items]
Litigation settlement through cash								$ 43,000,000
Shares issued on settlement | shares						0.9	0.6
Unfavorable Regulatory Action | CWA
Loss Contingencies [Line Items]
Number of mandatory facility specific factors. | Indicator																		5
Number of optional facility specific factors | Indicator																		6
Personal Injury or Wrongful Death Cases
Loss Contingencies [Line Items]
Reserves for litigation and regulatory proceedings			62,000,000													62,000,000		$ 62,000,000	68,000,000
Insurance receivables			$ 62,000,000													$ 62,000,000		$ 62,000,000	$ 68,000,000
Maximum [Member] | Subsequent Event | SCDOR
Loss Contingencies [Line Items]
Cash payment		$ 1,000,000
Carbon Regulations [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Significant emission rate per year CO2 equivalent | T															75,000
EPA
Loss Contingencies [Line Items]
Number of petition agreed for reconsideration | Petition													2
EPA | Unfavorable Regulatory Action | CWA | 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
EPA | Minimum [Member] | Unfavorable Regulatory Action | CWA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Loss contingencies Individual circumstances period										2021
EPA | Maximum [Member] | Unfavorable Regulatory Action | CWA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Loss contingencies Individual circumstances period										2028