Description Of Business (Details)	12 Months Ended
	Dec. 31, 2017 mi
Description Of Business [Line Items]
Electrification area	400
Matanuska Electric Association, Inc. [Member]
Description Of Business [Line Items]
Long-term Contract for Purchase of Electric Power, Date of Contract Extension	Apr. 30, 2015
Golden Valley Electric Association, Inc. [Member]
Description Of Business [Line Items]
Power contracts expiration date	Mar. 31, 2015