Commitments and Contingencies - Schedule of Subsidiary Guarantees (Detail)	Sep. 30, 2020 USD ($)
Guarantee Obligations [Line Items]
Maximum Exposure	$ 5,717,000,000	[1]
Commodity Transactions
Guarantee Obligations [Line Items]
Maximum Exposure	2,220,000,000	[2]
Nuclear Obligations
Guarantee Obligations [Line Items]
Maximum Exposure	224,000,000	[3]
Solar
Guarantee Obligations [Line Items]
Maximum Exposure	453,000,000	[4]
Other
Guarantee Obligations [Line Items]
Maximum Exposure	920,000,000	[5]
Cove Point
Guarantee Obligations [Line Items]
Maximum Exposure	$ 1,900,000,000	[6]

[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.

[2] Guarantees related to commodity commitments of certain subsidiaries. These guarantees were provided to counterparties in order to facilitate physical and financial transaction related commodities and services.

[3] Guarantees primarily related to certain DGI subsidiaries regarding all aspects of running a nuclear facility.

[4] Includes guarantees to facilitate the development of solar projects. Also includes guarantees entered into by DGI on behalf of certain subsidiaries to facilitate the acquisition and development of solar projects.

[5] Guarantees related to other miscellaneous contractual obligations such as leases, environmental obligations, construction projects and insurance programs. Due to the uncertainty of workers’ compensation claims, the parental guarantee has no stated limit.

[6] Guarantees related to Cove Point, in support of terminal services, transportation and construction. Cove Point has two guarantees that have no maximum limit and, therefore, are not included in this amount. As discussed in Note 3, in November 2020 Cove Point became an equity method investment of Dominion Energy.