Electric utility segment - Condensed consolidating statement of comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 65,032	$ 48,887	$ 33,420	$ 63,419	$ 42,512	$ 45,688	$ 147,339	$ 151,619
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	6,324			2,615			17,720	7,621
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(5,721)			(2,493)			(16,038)	(7,089)
Other comprehensive income, net of taxes	1,440	(332)	18,212	3,297	13,699	9,241	19,320	26,237
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	66,472			66,716			166,659	177,856
Consolidating adjustments
Condensed Statement of Income Captions [Line Items]
Net income for common stock	(14,912)			(11,048)			(37,492)	(30,983)
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	(1,655)			(696)			(4,456)	(1,978)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	1,654			696			4,454	1,976
Other comprehensive income, net of taxes	(1)			0			(2)	(2)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	(14,913)			(11,048)			(37,494)	(30,985)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	60,065			46,779			126,299	111,479
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	5,769			2,519			16,137	7,162
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(5,721)			(2,493)			(16,038)	(7,089)
Other comprehensive income, net of taxes	48			26			99	73
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	60,113			46,805			126,398	111,552
HELCO | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	8,060			5,269			21,306	15,104
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	885			387			2,384	1,091
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(887)			(387)			(2,382)	(1,089)
Other comprehensive income, net of taxes	(2)			0			2	2
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	8,058			5,269			21,308	15,106
Maui Electric | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	6,852			5,779			16,186	15,879
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	770			309			2,072	887
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(767)			(309)			(2,072)	(887)
Other comprehensive income, net of taxes	3			0			0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	6,855			5,779			16,186	15,879
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 taxes	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, 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	60,065	42,329	23,905	46,779	32,574	32,126	126,299	111,479
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	5,769			2,519			16,137	7,162
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(5,721)			(2,493)			(16,038)	(7,089)
Other comprehensive income, net of taxes	48	$ 25	$ 26	26	$ 23	$ 24	99	73
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	$ 60,113			$ 46,805			$ 126,398	$ 111,552