Bank segment - Comprehensive income data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 60,073	$ 127,142	$ 132,927	$ 203,622
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $(137), $1,417, $(1,619) and $(5,413), respectively	208	(2,147)	2,452	8,197
Reclassification adjustment for net realized gains included in net income, net of taxes	0	0	0	(360)
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 $138, $144, $675 and $421, respectively	3,942	3,641	11,793	10,877
Other comprehensive income (loss), net of taxes	554	(1,669)	3,909	9,239
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	60,627	125,473	136,836	212,861
Net unrealized gains (losses) on securities arising during the period, taxes (benefits)	137	(1,417)	1,619	5,413
Reclassification adjustment for sale of securities, tax (benefits)	0	0	0	238
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, tax benefits	(2,516)	(2,324)	(7,526)	(6,943)
American Savings Bank (ASB)
Condensed Statement of Income Captions [Line Items]
Net income for common stock	17,592	15,104	50,138	41,062
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $(137), $1,417, $(1,619) and $(5,413), respectively	208	(2,147)	2,452	8,197
Reclassification adjustment for net realized gains included in net income, net of taxes	0	0	0	(360)
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 $138, $144, $675 and $421, respectively	209	219	1,023	638
Other comprehensive income (loss), net of taxes	417	(1,928)	3,475	8,475
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	18,009	13,176	53,613	49,537
Net unrealized gains (losses) on securities arising during the period, taxes (benefits)	137	(1,417)	1,619	5,413
Reclassification adjustment for sale of securities, tax (benefits)	0	0	0	238
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, tax benefits	$ (138)	$ (144)	$ (675)	$ (421)