Property, Plant and Equipment (Narrative) (Detail)	1 Months Ended			3 Months Ended				9 Months Ended
	Oct. 31, 2024 USD ($)	Jul. 31, 2024 USD ($) a mi MW	Feb. 29, 2024 USD ($)	Sep. 30, 2024 USD ($)	Jun. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Property, Plant and Equipment [Line Items]
Impairment of assets and other charges				$ 122,000,000		$ 1,000,000		$ 219,000,000	$ 136,000,000
Minimum
Property, Plant and Equipment [Line Items]
Additional capital contribution percentage			67.00%
Maximum
Property, Plant and Equipment [Line Items]
Additional capital contribution percentage			83.00%
Corporate Office Building
Property, Plant and Equipment [Line Items]
Proceeds from sale of property, plant and equipment					$ 23,000,000
Level 3 | Corporate Office Building
Property, Plant and Equipment [Line Items]
Long-lived assets, estimated fair value					23,000,000		$ 35,000,000
Level 3 | Nonregulated renewable natural gas facilities | Minimum
Property, Plant and Equipment [Line Items]
Long-lived assets, estimated fair value				1,000,000	1,000,000			$ 1,000,000
Impairment of Assets and Other Charges | Corporate Office Building
Property, Plant and Equipment [Line Items]
Impairment of assets and other charges					17,000,000		91,000,000
Asset impairment charges after tax					12,000,000		$ 68,000,000
Impairment of Assets and Other Charges | Nonregulated renewable natural gas facilities
Property, Plant and Equipment [Line Items]
Impairment of assets and other charges				27,000,000	33,000,000
Asset impairment charges after tax				21,000,000	$ 25,000,000
Acquisition of Wind Project
Property, Plant and Equipment [Line Items]
Offshore wind project price expected		$ 160,000,000
Acquisition of Solar Project Foxhound Virginia
Property, Plant and Equipment [Line Items]
Date Agreement Entered								2023-03
Date Agreement Closed								February 2024
Date of Commercial Operations								April 2024
Acquisition Of Offshore Wind Project
Property, Plant and Equipment [Line Items]
Date Agreement Entered								2024-07
Date Agreement Closed								October 2024
Miles of area acquired | mi		27
Acres of area acquired | a		40,000
Power generating capacity | MW		800
CVOW Commercial Project Excluding Financing Costs | Subsequent Event
Property, Plant and Equipment [Line Items]
Total project costs	$ 9,800,000,000
CVOW Commercial Project Excluding Financing Costs Condition Two | Maximum | Subsequent Event
Property, Plant and Equipment [Line Items]
Total project costs	$ 11,300,000,000
Virginia Power and Stonepeak | Maximum
Property, Plant and Equipment [Line Items]
Total project costs			$ 11,300,000,000
Virginia Power and Stonepeak | CVOW Commercial Project
Property, Plant and Equipment [Line Items]
Remaining capital percentage			50.00%
Virginia Electric and Power Company | Subsequent Event
Property, Plant and Equipment [Line Items]
Percentage of proceeds from sale of non controlling interests in CVOW commercial project	50.00%
Virginia Electric and Power Company | Minimum
Property, Plant and Equipment [Line Items]
Total project costs			$ 13,700,000,000
Virginia Electric and Power Company | Impairment of Assets and Other Charges
Property, Plant and Equipment [Line Items]
Impairment of assets and other charges				25,000,000
Asset impairment charges after tax				$ 18,000,000
Virginia Electric and Power Company | CVOW Commercial Project
Property, Plant and Equipment [Line Items]
Ownership percentage			50.00%
Virginia Electric and Power Company | CVOW Commercial Project | Minimum | Subsequent Event
Property, Plant and Equipment [Line Items]
Initial withholding amount	$ 145,000,000
Virginia Electric and Power Company | CVOW Commercial Project Excluding Financing Costs | Subsequent Event
Property, Plant and Equipment [Line Items]
Initial withholding amount	100,000,000
Virginia Electric and Power Company | CVOW Commercial Project Excluding Financing Costs Condition Two | Subsequent Event
Property, Plant and Equipment [Line Items]
Proceeds from sale of non controlling interests in CVOW commercial project	$ 2,600,000,000
Stonepeak | Minimum
Property, Plant and Equipment [Line Items]
Total project costs			$ 11,300,000,000
Stonepeak | Maximum
Property, Plant and Equipment [Line Items]
Total project costs			13,700,000,000
Additional capital costs			$ 11,300,000,000