Significant Financing Transactions (Narrative) (Detail)		1 Months Ended									3 Months Ended			9 Months Ended		12 Months Ended
		Nov. 30, 2021 USD ($)	Aug. 31, 2021 USD ($) shares	Jul. 31, 2021 USD ($) shares	Jun. 30, 2021 USD ($)	Apr. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($) agreement shares	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) shares		Nov. 30, 2020 USD ($)	Jul. 31, 2020 USD ($)
Debt Instrument [Line Items]
Facility Limit	[1]											$ 6,000,000,000		$ 6,000,000,000
Credit facility, amount borrowed												900,000,000		900,000,000
Short-term debt												3,885,000,000		3,885,000,000		$ 895,000,000	[2]
Debt, amount redeemed			$ 39,000,000
Other long-term debt												$ 849,000,000		$ 849,000,000		881,000,000	[2]
Preferred stock shares authorized | shares												20,000,000		20,000,000
Stock purchase contract liability												$ 65,000,000		$ 65,000,000		129,000,000
Corporate units stock purchase contract liability payments														64,000,000	$ 62,000,000
Issuance of common stock														144,000,000	159,000,000
Issuance of stock												$ 195,000,000	$ 333,000,000	$ 292,000,000	481,000,000
Stock repurchased, value													2,385,000,000		2,385,000,000
Number of prepaid accelerated share repurchase agreements | agreement								2
Decrease in common stock													1,500,000,000
Common stock worth based on closing Price								$ 1,500,000,000					$ 1,500,000,000		$ 1,500,000,000
Common Stock
Debt Instrument [Line Items]
Issuance of stock (in shares) | shares			600,000	1,400,000				4,100,000				3,000,000	4,000,000	4,000,000	6,000,000
Issuance of stock			$ 45,000,000	$ 104,000,000								$ 195,000,000	$ 333,000,000	$ 292,000,000	$ 481,000,000
Stock repurchase program, authorized amount																		$ 1,000,000,000.0	$ 3,000,000,000.0
Stock repurchased, shares | shares								4,100,000					28,000,000	0	28,000,000
Stock repurchased, value								$ 323,000,000					$ 2,385,000,000		$ 2,385,000,000
Accelerated share repurchase, payments								$ 1,500,000,000					$ 1,500,000,000		$ 1,500,000,000
Accelerated share repurchase, cash paid for number of shares exchange | shares								17,200,000					17,200,000		17,200,000
Common Stock | Open Market Agreement
Debt Instrument [Line Items]
Stock repurchased, shares | shares													7,200,000
Stock repurchased, value													$ 562,000,000
Series A Preferred Stock
Debt Instrument [Line Items]
Recorded dividend												$ 7,000,000	$ 7,000,000	$ 21,000,000	$ 21,000,000
Recorded dividends per share | $ / shares												$ 4.375	$ 4.375	$ 13.125	$ 13.125
Conversion of stock, description														Series A Preferred Stock be settled, at Dominion Energy’s election, either entirely in cash or in cash up to the first $1,000 per share and in shares of Dominion Energy common stock, cash or any combination thereof for any amounts in excess of $1,000 per share.
Series A Preferred Stock | Scenario Forecast
Debt Instrument [Line Items]
Reclassifications of permanent to mezzanine equity											$ 1,600,000
Series B Preferred Stock
Debt Instrument [Line Items]
Recorded dividend												$ 9,000,000	$ 9,000,000	$ 27,000,000	$ 27,000,000
Recorded dividends per share | $ / shares												$ 11.625	$ 11.625	$ 34.875	$ 34.875
Interest Rate Swaps
Debt Instrument [Line Items]
Derivative notional value									$ 2,000,000,000.0
Derivative maturity month and year									2024-12
Other long-term debt																326,000,000
Various Programs
Debt Instrument [Line Items]
Issuance of common stock														$ 292,000,000	$ 481,000,000
Issuance of stock (in shares) | shares														4,000,000	6,200,000
Floating Rate Demand Notes
Debt Instrument [Line Items]
Short-term debt												$ 391,000,000		$ 391,000,000		268,000,000
Floating Rate Demand Notes | Shelf Registration for Sale of Demand Notes
Debt Instrument [Line Items]
Facility Limit																3,000,000,000.0
Senior Notes Due in 2051 | PSNC
Debt Instrument [Line Items]
Total Long-term Debt							$ 150,000,000
Interest rate percentage							3.10%
Debt maturity year							2051
Senior Notes Due in 2026
Debt Instrument [Line Items]
Total Long-term Debt						$ 600,000,000
Interest rate percentage						1.45%
Debt maturity year						2026
Senior Notes Due in 2041
Debt Instrument [Line Items]
Total Long-term Debt						$ 500,000,000
Interest rate percentage						3.30%
Debt maturity year						2041
2.0% Senior Notes Due August 2021
Debt Instrument [Line Items]
Debt maturity month and year				2021-08
Interest rate percentage				2.00%
Debt, amount redeemed				$ 400,000,000
Senior Notes Due in 2031
Debt Instrument [Line Items]
Total Long-term Debt			$ 1,000,000,000.0
Interest rate percentage			2.25%
Debt maturity year			2031
July 2016 Hybrids | Unsecured Junior Subordinated Notes
Debt Instrument [Line Items]
Debt maturity year			2076
Debt, amount redeemed			$ 800,000,000
Expenses related to early redemption of hybrids			23,000,000
DESC
Debt Instrument [Line Items]
Facility Limit												500,000,000		500,000,000
Short-term indebtedness outstanding							$ 2,200,000,000
Debt maturity month and year							2023-03
DESC | 3.22% First Mortgage Bond Due October 2021
Debt Instrument [Line Items]
Debt maturity month and year				2021-10
Interest rate percentage				3.22%
Debt, amount redeemed				$ 30,000,000
Questar Gas
Debt Instrument [Line Items]
Facility Limit												250,000,000		250,000,000
Questar Gas | 2.21% Senior Notes Due In 2031
Debt Instrument [Line Items]
Total Long-term Debt			$ 125,000,000
Interest rate percentage			2.21%
Debt maturity year			2031
Questar Gas | 3.15% Senior Notes Due In 2051
Debt Instrument [Line Items]
Total Long-term Debt			$ 125,000,000
Interest rate percentage			3.15%
Debt maturity year			2051
GENCO
Debt Instrument [Line Items]
Short-term indebtedness outstanding							$ 200,000,000
Debt maturity month and year							2023-03
SBL Holdco | Credit Facilities, Maturing in December 2017 with 1 year Automatic Renewals through 2023
Debt Instrument [Line Items]
Facility Limit												30,000,000		$ 30,000,000
Automatic renewal period														1 year
Short-term debt												0		$ 0		0
Dominion Solar Projects III, Inc | Credit Facilities, Maturing in May 2018 with 1 year Automatic Renewals through 2024
Debt Instrument [Line Items]
Facility Limit												25,000,000		$ 25,000,000
Automatic renewal period														1 year
Short-term debt												0		$ 0		0
Virginia Electric and Power Company
Debt Instrument [Line Items]
Facility Limit	[3]											6,000,000,000		6,000,000,000
Short-term debt												896,000,000		896,000,000		45,000,000	[4]
Other long-term debt												$ 495,000,000		$ 495,000,000		480,000,000	[4]
Issuance of stock (in shares) | shares												0	0	0	0
Virginia Electric and Power Company | Interest Rate Swaps
Debt Instrument [Line Items]
Derivative notional value			$ 900,000,000
Derivative maturity month and year			2023-12
Other long-term debt																$ 443,000,000
Virginia Electric and Power Company | 2.95% Senior Notes Due In January 2022
Debt Instrument [Line Items]
Debt maturity month and year		2022-01
Interest rate percentage		2.95%
Debt, amount redeemed		$ 450,000,000
Dominion Energy
Debt Instrument [Line Items]
Preferred stock shares issued | shares												2,400,000		2,400,000		2,400,000
Preferred stock shares outstanding | shares												2,400,000		2,400,000		2,400,000
Dominion Energy | Series A Preferred Stock
Debt Instrument [Line Items]
Preferred stock shares issued | shares												1,600,000		1,600,000		1,600,000
Preferred stock shares outstanding | shares												1,600,000		1,600,000		1,600,000
Dominion Energy | Series B Preferred Stock
Debt Instrument [Line Items]
Preferred stock shares issued | shares												800,000		800,000		800,000
Preferred stock shares outstanding | shares												800,000		800,000		800,000
New Joint Revolving Credit Facility
Debt Instrument [Line Items]
Facility Limit					$ 6,000,000,000.0
Letter of Credit
Debt Instrument [Line Items]
Facility Limit												$ 2,000,000,000.0		$ 2,000,000,000.0
Letter of Credit | Credit Facility, Maturing in June 2022
Debt Instrument [Line Items]
Facility Limit												30,000,000		30,000,000
Credit facility, amount borrowed												29,000,000		$ 29,000,000		$ 30,000,000
Line of credit facility, maturity date														Jun. 30, 2022
Letter of Credit | Virginia Electric and Power Company
Debt Instrument [Line Items]
Facility Limit												2,000,000,000.0		$ 2,000,000,000.0
364-Day Revolving Credit Facility
Debt Instrument [Line Items]
Facility Limit										$ 900,000,000
Short-term debt																$ 225,000,000
Debt Instrument Term										364 days				364 days		364 days
Term Loan Credit Agreement
Debt Instrument [Line Items]
Facility Limit				$ 1,300,000,000
Sustainability Revolving Credit Agreement | Credit Facility, Maturing in June 2024
Debt Instrument [Line Items]
Facility Limit					$ 900,000,000
Credit facility, amount borrowed												$ 900,000,000		$ 900,000,000
Line of credit facility, maturity date					Jun. 30, 2024
Fund used for environmental sustainability and social investment initiatives					$ 250,000,000
Fund used for general corporate purposes					$ 650,000,000

[1] This credit facility matures in June 2026, with the potential to be extended by the borrowers to June 2028, and can be used by the borrowers under the credit facility to support bank borrowings and the issuance of commercial paper, as well as to support up to a combined $2.0 billion of letters of credit.

[2] Dominion Energy’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.

[3] The full amount of the facility is available to Virginia Power, less any amounts outstanding to co-borrowers Dominion Energy, Questar Gas and DESC. The sub-limit for Virginia Power is set pursuant to the terms of the facility but can be changed at the option of the borrowers multiple times per year. At September 30, 2021, the sub-limit for Virginia Power was $1.75 billion. If Virginia Power has liquidity needs in excess of its sub-limit, the sub-limit may be changed or such needs may be satisfied through short-term intercompany borrowings from Dominion Energy. This credit facility matures in June 2026, with the potential to be extended by the borrowers to June 2028. The credit facility can be used to support bank borrowings and the issuance of commercial paper, as well as to support up to $2.0 billion (or the sub-limit, whichever is less) of letters of credit.

[4] Virginia Power’s Consolidated Balance Sheet at December 31, 2020 has been derived from the audited Consolidated Balance Sheet at that date.