Bank segment (HEI only) - Statements of Comprehensive Income - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Statement of Income Captions [Line Items]
Net unrealized loss on available-for-sale securities, tax benefits	$ 3,468	$ 2,886	$ 3,763
Reclassification adjustment for net realized gains included in net income, tax expenses	0	0	238
Net gains (losses) arising during the period, retirement benefits, taxes	9,810	(41,129)	27,703
Amortization of net loss, prior service gain and transition obligation included in net periodic benefit cost, tax benefits	7,317	10,041	9,267
American Savings Bank (ASB)
Condensed Statement of Income Captions [Line Items]
Net unrealized loss on available-for-sale securities, tax benefits	3,468	2,886	3,763
Reclassification adjustment for net realized gains included in net income, tax expenses	0	0	238
Net gains (losses) arising during the period, retirement benefits, taxes	0	0	0
Amortization of net loss, prior service gain and transition obligation included in net periodic benefit cost, tax benefits	$ 1,108	$ 812	$ 566