Electric utility segment - Condensed consolidating statement of comprehensive income (loss) (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
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	2,615			5,259			7,621	15,755
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,493)			(4,725)			(7,089)	(14,174)
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
Consolidating adjustments
Condensed Statement of Income Captions [Line Items]
Net income for common stock	(11,048)			(16,636)			(30,983)	(35,041)
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	(696)			(1,311)			(1,978)	(3,931)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	696			1,311			1,976	3,930
Other comprehensive income (loss), net of taxes	0			0			(2)	(1)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	(11,048)			(16,636)			(30,985)	(35,042)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	46,779			49,712			111,479	108,356
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	2,519			4,753			7,162	14,259
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,493)			(4,725)			(7,089)	(14,174)
Other comprehensive income (loss), net of taxes	26			28			73	85
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	46,805			49,740			111,552	108,441
HELCO | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	5,269			9,175			15,104	19,039
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	387			705			1,091	2,114
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(387)			(705)			(1,089)	(2,113)
Other comprehensive income (loss), net of taxes	0			0			2	1
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	5,269			9,175			15,106	19,040
Maui Electric | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	5,779			7,461			15,879	16,002
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	309			606			887	1,817
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(309)			(606)			(887)	(1,817)
Other comprehensive income (loss), net of taxes	0			0			0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	5,779			7,461			15,879	16,002
Other subsidiaries | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	0			0			0	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 tax benefits	0			0			0	0
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	0			0			0	0
Other comprehensive income (loss), net of taxes	0			0			0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	0			0			0	0
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income for common stock	46,779	32,574	32,126	49,712	31,169	27,475	111,479	108,356
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	2,519			4,753			7,162	14,259
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,493)			(4,725)			(7,089)	(14,174)
Other comprehensive income (loss), net of taxes	26	$ 23	$ 24	28	$ 26	$ 31	73	85
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	$ 46,805			$ 49,740			$ 111,552	$ 108,441