Commitments and Contingencies - Schedule of Subsidiary Guarantees (Detail)	Sep. 30, 2021 USD ($)
Guarantee Obligations [Line Items]
Maximum Exposure	$ 3,851,000,000	[1]
Commodity Transactions
Guarantee Obligations [Line Items]
Maximum Exposure	1,892,000,000	[2]
Nuclear Obligations
Guarantee Obligations [Line Items]
Maximum Exposure	242,000,000	[3]
Solar
Guarantee Obligations [Line Items]
Maximum Exposure	463,000,000	[4]
Other
Guarantee Obligations [Line Items]
Maximum Exposure	$ 1,254,000,000	[5]

[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.

[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. Also includes guarantees entered into by Dominion Energy RNG Holdings II, Inc. on behalf of a subsidiary to facilitate construction of renewable natural gas facilities. Due to the uncertainty of workers’ compensation claims, the parental guarantee has no stated limit.