Commitments and Contingencies (Guarantees, Surety Bonds and Letters of Credit) (Detail)	Sep. 30, 2020 USD ($)
Guarantee Obligations [Line Items]
Maximum Exposure	$ 5,717,000,000	[1]
Financial Guarantee | Third Parties
Guarantee Obligations [Line Items]
Maximum Exposure	10,000,000
Surety Bond
Guarantee Obligations [Line Items]
Maximum Exposure	156,000,000
Surety Bond | Virginia Electric and Power Company
Guarantee Obligations [Line Items]
Maximum Exposure	90,000,000
Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Maximum Exposure	$ 96,000,000

[1] Excludes Dominion Energy's guarantees for the new corporate office properties discussed in Note 15 to the Consolidated Financial Statements in the Companies’ Annual Report on Form 10-K for the year ended December 31, 2019 and in Note 14 in this report.