Electric utility segment - Condensed consolidating statement of comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 63,415	$ 63,872	$ 64,358	$ 65,032	$ 48,887	$ 33,420	$ 191,645	$ 147,339
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	2,853			6,324			14,871	17,720
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,799)			(5,721)			(14,421)	(16,038)
Other comprehensive income (loss), net of taxes	(11,305)	16,472	(44,016)	1,440	(332)	18,212	(38,849)	19,320
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	52,110			66,472			152,796	166,659
Hawaiian Electric Consolidated
Condensed Statement of Income Captions [Line Items]
Net income for common stock	50,342	41,901	43,358	60,065	42,329	23,905	135,601	126,299
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	2,905			5,769			14,596	16,137
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,799)			(5,721)			(14,421)	(16,038)
Other comprehensive income (loss), net of taxes	106	$ 35	$ 34	48	$ 25	$ 26	175	99
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	50,448			60,113			135,776	126,398
Hawaiian Electric Consolidated | Reportable Legal Entities | Hawaiian Electric Industries, Inc.
Condensed Statement of Income Captions [Line Items]
Net income for common stock	50,342			60,065			135,601	126,299
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	2,905			5,769			14,596	16,137
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(2,799)			(5,721)			(14,421)	(16,038)
Other comprehensive income (loss), net of taxes	106			48			175	99
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	50,448			60,113			135,776	126,398
Hawaiian Electric Consolidated | Reportable Legal Entities | Hawaii Electric Light
Condensed Statement of Income Captions [Line Items]
Net income for common stock	4,888			8,060			17,187	21,306
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	393			885			2,062	2,384
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(391)			(887)			(2,059)	(2,382)
Other comprehensive income (loss), net of taxes	2			(2)			3	2
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	4,890			8,058			17,190	21,308
Hawaiian Electric Consolidated | Reportable Legal Entities | Maui Electric
Condensed Statement of Income Captions [Line Items]
Net income for common stock	7,140			6,852			18,095	16,186
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	393			770			1,915	2,072
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(393)			(767)			(1,915)	(2,072)
Other comprehensive income (loss), net of taxes	0			3			0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	7,140			6,855			18,095	16,186
Hawaiian Electric Consolidated | Reportable Legal Entities | Other subsidiaries
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 (loss), net of taxes	0			0			0	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	0			0			0	0
Hawaiian Electric Consolidated | Consolidating adjustments
Condensed Statement of Income Captions [Line Items]
Net income for common stock	(12,028)			(14,912)			(35,282)	(37,492)
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	(786)			(1,655)			(3,977)	(4,456)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	784			1,654			3,974	4,454
Other comprehensive income (loss), net of taxes	(2)			(1)			(3)	(2)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	$ (12,030)			$ (14,913)			$ (35,285)	$ (37,494)