Electric utility segment - Condensed consolidating statement of comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 48,887	$ 33,420	$ 42,512	$ 45,688	$ 82,307	$ 88,200
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	5,690		2,503		11,396	5,006
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(5,159)		(2,298)		(10,317)	(4,596)
Other comprehensive income (loss), net of taxes	(332)	18,212	13,699	9,241	17,880	22,940
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	48,555		56,211		100,187	111,140
Consolidating adjustments
Condensed Statement of Income Captions [Line Items]
Net income for common stock	(13,776)		(8,086)		(22,580)	(19,935)
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	(1,401)		(641)		(2,801)	(1,282)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	1,401		640		2,800	1,280
Other comprehensive income (loss), net of taxes	0		(1)		(1)	(2)
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	(13,776)		(8,087)		(22,581)	(19,937)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	42,329		32,574		66,234	64,700
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	5,184		2,321		10,368	4,643
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(5,159)		(2,298)		(10,317)	(4,596)
Other comprehensive income (loss), net of taxes	25		23		51	47
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	42,354		32,597		66,285	64,747
HELCO | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	7,179		4,666		13,246	9,835
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	751		352		1,499	704
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(748)		(351)		(1,495)	(702)
Other comprehensive income (loss), net of taxes	3		1		4	2
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	7,182		4,667		13,250	9,837
Maui Electric | Reportable Legal Entities
Condensed Statement of Income Captions [Line Items]
Net income for common stock	6,597		3,420		9,334	10,100
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	650		289		1,302	578
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(653)		(289)		(1,305)	(578)
Other comprehensive income (loss), net of taxes	(3)		0		(3)	0
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	6,594		3,420		9,331	10,100
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 (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	42,329	23,905	32,574	32,126	66,234	64,700
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	5,184		2,321		10,368	4,643
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes	(5,159)		(2,298)		(10,317)	(4,596)
Other comprehensive income (loss), net of taxes	25	$ 26	23	$ 24	51	47
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	$ 42,354		$ 32,597		$ 66,285	$ 64,747