Electric utility segment - Consolidating Statement of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 50,485	$ 65,032	$ 48,887	$ 33,420	$ 66,263	$ 63,419	$ 42,512	$ 45,688	$ 197,824	$ 217,882	$ 201,774
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									(60,529)	10,914	(28,101)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									23,689	10,107	21,015
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									39,860	(16,177)	8,325
Other comprehensive income (loss), net of taxes									18,775	30,571	(8,669)
Comprehensive income									216,599	248,453	193,105
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 43,041	$ 60,065	$ 42,329	$ 23,905	$ 45,361	$ 46,779	$ 32,574	$ 32,126	169,340	156,840	143,653
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									(63,050)	5,249	(26,019)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									21,550	9,550	19,012
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									39,860	(16,177)	8,325
Other comprehensive income (loss), net of taxes									(1,640)	(1,378)	1,318
Comprehensive income									167,700	155,462	144,971
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Hawaiian Electric (parent only)
Condensed Statement of Income Captions [Line Items]
Net income for common stock									169,340	156,840	143,653
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									(63,050)	5,249	(26,019)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									21,550	9,550	19,012
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									39,860	(16,177)	8,325
Other comprehensive income (loss), net of taxes									(1,640)	(1,378)	1,318
Comprehensive income									167,700	155,462	144,971
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | HELCO
Condensed Statement of Income Captions [Line Items]
Net income for common stock									27,493	20,817	24,481
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									(9,424)	373	(6,090)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									3,179	1,455	2,819
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									6,025	(1,840)	3,305
Other comprehensive income (loss), net of taxes									(220)	(12)	34
Comprehensive income									27,273	20,805	24,515
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Maui Electric
Condensed Statement of Income Captions [Line Items]
Net income for common stock									20,011	22,350	20,912
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									(10,897)	(204)	(5,004)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									2,763	1,182	2,423
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									8,000	(1,152)	2,788
Other comprehensive income (loss), net of taxes									(134)	(174)	207
Comprehensive income									19,877	22,176	21,119
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
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									(47,504)	(43,167)	(45,393)
Retirement benefit plans:
Net gains (losses) arising during the period, net of (taxes) benefits									20,321	(169)	11,094
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits									(5,942)	(2,637)	(5,242)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits									(14,025)	2,992	(6,093)
Other comprehensive income (loss), net of taxes									354	186	(241)
Comprehensive income									$ (47,150)	$ (42,981)	$ (45,634)