Commitments and Contingencies (Guarantees, Surety Bonds and Letters of Credit) (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($) Guarantee
Guarantee Obligations [Line Items]
Guarantee liability	$ 3,527,000,000	[1]
Equity Method Investee | Cove Point
Guarantee Obligations [Line Items]
Number of guarantees with maximum limit | Guarantee	2
Number of guarantees with no maximum limit | Guarantee	2
Guarantees with Maximum Limit [Member] | Equity Method Investee | Cove Point
Guarantee Obligations [Line Items]
Guarantee liability	$ 1,900,000,000
Guarantees with No Maximum Limit [Member] | Equity Method Investee | Cove Point
Guarantee Obligations [Line Items]
Guarantee liability	$ 0
Financial Guarantee | Equity Method Investee | Cove Point
Guarantee Obligations [Line Items]
Number of Guarantee | Guarantee	4
Surety Bond
Guarantee Obligations [Line Items]
Guarantee liability	$ 157,000,000
Surety Bond | Virginia Electric and Power Company
Guarantee Obligations [Line Items]
Guarantee liability	88,000,000
Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability	$ 100,000,000

[1] Excludes Dominion Energy’s guarantees for the new corporate office properties and an offshore wind installation vessel discussed in Note 15.