Bank segment - Comprehensive income data (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 63,419	$ 42,512	$ 45,688	$ 65,900	$ 46,054	$ 40,247	$ 151,619	$ 152,201
Net unrealized gains (losses) on available-for-sale investment securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $(1,557), $1,876, $(10,194) and $8,335, respectively	4,253			(5,123)			27,846	(22,768)
Reclassification adjustment for net realized gains included in net income, net of taxes of $175, nil, $175, and nil, respectively	(478)			0			(478)	0
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of (taxes) benefits of $13, $141, $(1,109) and $968, respectively	2,615			5,259			7,621	15,755
Other comprehensive income (loss), net of taxes	3,297	$ 13,699	$ 9,241	(4,589)	$ (3,825)	$ (12,773)	26,237	(21,187)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	66,716			61,311			177,856	131,014
Net unrealized gains (losses) on securities arising during the period, (taxes) benefits	(1,557)			1,876			(10,194)	8,335
Reclassification adjustment for net realized gains included in net income, taxes	175			0			175	0
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, (taxes) benefits	741			1,832			2,482	5,486
American Savings Bank (ASB)
Condensed Statement of Income Captions [Line Items]
Net income for common stock	22,888			21,221			60,743	60,742
Net unrealized gains (losses) on available-for-sale investment securities:
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of (taxes) benefits of $(1,557), $1,876, $(10,194) and $8,335, respectively	4,253			(5,123)			27,846	(22,768)
Reclassification adjustment for net realized gains included in net income, net of taxes of $175, nil, $175, and nil, respectively	(478)			0			(478)	0
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of (taxes) benefits of $13, $141, $(1,109) and $968, respectively	34			382			(3,032)	1,970
Other comprehensive income (loss), net of taxes	3,809			(4,741)			24,336	(20,798)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	26,697			16,480			85,079	39,944
Net unrealized gains (losses) on securities arising during the period, (taxes) benefits	(1,557)			1,876			(10,194)	8,335
Reclassification adjustment for net realized gains included in net income, taxes	175			0			175	0
Amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, (taxes) benefits	$ 13			$ 141			$ (1,109)	$ 968