Regulatory restrictions on net assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Regulatory restrictions on net assets
Distribution restrictions, percent of earnings in current year and 5 preceding years if capitalization rate is less than 35%	80.00%
Total capitalization rate of HEI's electric utility subsidiaries	57.00%
Common stock equity	$ 2,162,280	$ 2,097,386	$ 2,066,753	$ 1,927,640
Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory restrictions on net assets
Restrictions on transfer of net assets to the parent in the form of cash dividends, loans and advances	782,000
Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory restrictions on net assets
Common stock equity	1,957,641	1,845,283	$ 1,799,787	$ 1,728,325
American Savings Bank (ASB)
Regulatory restrictions on net assets
Common stock equity	634,389	$ 606,847
Restrictions on transfer of net assets to the parent in the form of cash dividends, loans and advances	$ 474,000