Wholesale Power Contracts - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021 member MW
Wholesale Power Contracts [Line Items]
Required period for termination of wholesale power contract	3 years
Purchases under limited contract exceptions, percent of power received from owned generation or other suppliers	5.00%
Description of limited exceptions	There are two additional limited exceptions to the all-requirements nature of the contracts. One exception permits each of our member distribution cooperatives, with 180 days prior written notice, to receive up to the greater of
Purchases under limited contract exceptions, amount of power allowable under contractual exception received from owned generation or other suppliers	5
Current maximum reduction in demand and associated energy	178
Maximum [Member]
Wholesale Power Contracts [Line Items]
Exception for purchases of hydroelectric power allocated from SEPA	2.00%
Mainland Virginia [Member]
Wholesale Power Contracts [Line Items]
Principal exceptions to the all-requirements obligations by members | member	8