Bank segment - Comprehensive income data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 65,900	$ 60,073	$ 152,201	$ 132,927
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of tax benefits (taxes) of $1,876, $(137), $8,335 and $(1,619), respectively	(5,123)	208	(22,768)	2,452
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $141, $138, $968 and $675, respectively	5,259	3,942	15,755	11,793
Other comprehensive income (loss), net of taxes	(4,589)	554	(21,187)	3,909
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	61,311	60,627	131,014	136,836
Net unrealized gains (losses) on securities arising during the period, (taxes) benefits	1,876	(137)	8,335	(1,619)
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, taxes (benefits)	(1,832)	(2,516)	(5,486)	(7,526)
American Savings Bank (ASB)
Condensed Statement of Income Captions [Line Items]
Net income for common stock	21,221	17,592	60,742	50,138
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of tax benefits (taxes) of $1,876, $(137), $8,335 and $(1,619), respectively	(5,123)	208	(22,768)	2,452
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $141, $138, $968 and $675, respectively	382	209	1,970	1,023
Other comprehensive income (loss), net of taxes	(4,741)	417	(20,798)	3,475
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	16,480	18,009	39,944	53,613
Net unrealized gains (losses) on securities arising during the period, (taxes) benefits	1,876	(137)	8,335	(1,619)
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, taxes (benefits)	$ (141)	$ (138)	$ (968)	$ (675)