Electric utility segment - Consolidating Statement of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 66,263	$ 63,419	$ 42,512	$ 45,688	$ 49,573	$ 65,900	$ 46,054	$ 40,247	$ 217,882	$ 201,774	$ 165,297
Derivatives qualified as cash flow hedges:
Reclassification adjustment to net income, net of (taxes) benefit									0	0	454
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									10,914	(28,101)	65,531
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									10,107	21,015	15,737
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									(16,177)	8,325	(78,724)
Other comprehensive income (loss), net of taxes									30,571	(8,669)	(1,372)
Comprehensive income									248,453	193,105	163,925
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 45,361	$ 46,779	$ 32,574	$ 32,126	$ 35,297	$ 49,712	$ 31,169	$ 27,475	156,840	143,653	119,951
Derivatives qualified as cash flow hedges:
Reclassification adjustment to net income, net of (taxes) benefit									0	0	454
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									5,249	(26,019)	63,105
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									9,550	19,012	14,477
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									(16,177)	8,325	(78,724)
Other comprehensive income (loss), net of taxes									(1,378)	1,318	(688)
Comprehensive income									155,462	144,971	119,263
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Parent Company
Condensed Statement of Income Captions [Line Items]
Net income for common stock									156,840	143,653	119,951
Derivatives qualified as cash flow hedges:
Reclassification adjustment to net income, net of (taxes) benefit											454
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									5,249	(26,019)	63,105
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									9,550	19,012	14,477
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									(16,177)	8,325	(78,724)
Other comprehensive income (loss), net of taxes									(1,378)	1,318	(688)
Comprehensive income									155,462	144,971	119,263
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Hawaii Electric Light
Condensed Statement of Income Captions [Line Items]
Net income for common stock									20,817	24,481	20,146
Derivatives qualified as cash flow hedges:
Reclassification adjustment to net income, net of (taxes) benefit											0
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									373	(6,090)	3,093
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									1,455	2,819	1,903
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									(1,840)	3,305	(4,994)
Other comprehensive income (loss), net of taxes									(12)	34	2
Comprehensive income									20,805	24,515	20,148
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Maui Electric
Condensed Statement of Income Captions [Line Items]
Net income for common stock									22,350	20,912	17,911
Derivatives qualified as cash flow hedges:
Reclassification adjustment to net income, net of (taxes) benefit											0
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									(204)	(5,004)	7,329
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									1,182	2,423	1,619
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									(1,152)	2,788	(9,003)
Other comprehensive income (loss), net of taxes									(174)	207	(55)
Comprehensive income									22,176	21,119	17,856
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Other subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income for common stock									0	0	0
Derivatives qualified as cash flow hedges:
Reclassification adjustment to net income, net of (taxes) benefit											0
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									0	0	0
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
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									0	0	0
Other comprehensive income (loss), net of taxes									0	0	0
Comprehensive income									0	0	0
Hawaiian Electric Company, Inc. and Subsidiaries | Consolidating Adjustments
Condensed Statement of Income Captions [Line Items]
Net income for common stock									(43,167)	(45,393)	(38,057)
Derivatives qualified as cash flow hedges:
Reclassification adjustment to net income, net of (taxes) benefit											0
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									(169)	11,094	(10,422)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									(2,637)	(5,242)	(3,522)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									2,992	(6,093)	13,997
Other comprehensive income (loss), net of taxes									186	(241)	53
Comprehensive income									$ (42,981)	$ (45,634)	$ (38,004)