Wholesale Power Contracts - Additional Information (Details)	12 Months Ended
	Dec. 31, 2016 member MW
Wholesale Power Contracts [Abstract]
Required period for termination of wholesale power contract	3 years
Wholesale Power Contracts [Line Items]
Purchases under principal contract exceptions, percent of energy requirements	2.00%
Purchases under limited contract exceptions, percent of power received from owned generation or other suppliers	5.00%
Purchases under limited contract exceptions, amount of power received from owned generation or other suppliers	5
Current impact reduction in demand and associated energy	175
Power received under limited exceptions to wholesale power contract	60
Mainland Virginia [Member]
Wholesale Power Contracts [Line Items]
Principal exceptions to the all-requirements obligations by members | member	8