Commitments and Contingencies (Guarantees, Surety Bonds and Letters of Credit) (Detail)	9 Months Ended
	Sep. 30, 2021 USD ($) Guarantee
Guarantee Obligations [Line Items]
Guarantee liability	$ 3,851,000,000	[1]
Financial Guarantee | Equity Method Investee | Cove Point
Guarantee Obligations [Line Items]
Number of Guarantee | Guarantee	4
Guarantees with Maximum Limit [Member] | Equity Method Investee | Cove Point
Guarantee Obligations [Line Items]
Number of Guarantee | Guarantee	2
Guarantee liability	$ 1,900,000,000
Guarantees with No Maximum Limit [Member] | Equity Method Investee | Cove Point
Guarantee Obligations [Line Items]
Number of Guarantee | Guarantee	2
Guarantee liability	$ 0
Additional Guarantees [Member]
Guarantee Obligations [Line Items]
Guarantee liability	25,000,000
Surety Bond
Guarantee Obligations [Line Items]
Guarantee liability	169,000,000
Surety Bond | Virginia Electric and Power Company
Guarantee Obligations [Line Items]
Guarantee liability	95,000,000
Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability	$ 99,000,000

[1] Excludes Dominion Energy's guarantees for the new corporate office property and an offshore wind installation vessel discussed in Note 15 to the Consolidated Financial Statements in the Companies’ Annual Report on Form 10-K for the year ended December 31, 2020.