Retirement benefits - Changes in Projected Benefit Obligations and Fair Value of Plan Assets and Amounts Recognized in OCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined benefit pension and other postretirement benefit plans liability	$ (321,780)	$ (530,532)
Pension benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, balance at the beginning of the period	2,624,530	2,278,283
Service cost	81,432	73,387	$ 62,135
Interest cost	75,361	81,335	84,267
Actuarial (gains) losses	(43,300)	275,973
Participants contributions	0	0
Benefits paid and expenses	(93,384)	(84,448)
Benefit obligation, balance at the end of the period	2,644,639	2,624,530	2,278,283
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, balance at the beginning of the period	2,089,491	1,799,200
Actual return on plan assets	271,443	302,566
Employer contributions	51,777	70,844
Participants contributions	0	0
Benefits paid and expenses	(91,966)	(83,119)
Fair value of plan assets, balance at the end of the period	2,320,745	2,089,491	1,799,200
Accrued benefit asset (liability), balance	(323,894)	(535,039)
Other assets	23,675	25,851
Defined benefit pension and other postretirement benefit plans liability	(347,569)	(560,890)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income [Roll Forward]
AOCI debit/(credit), balance at beginning of the period (excluding impact of PUC D&Os)	557,564	503,821
Recognized during year – prior service credit (cost)	0	(8)
Recognized during year – net actuarial loss	(27,245)	(33,456)
Occurring during year – net actuarial loss (gain)	(182,520)	87,207
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os)	347,799	557,564	503,821
Cumulative impact of PUC D&Os	(324,162)	(534,594)
AOCI debit/(credit), balance at end of the period	23,637	22,970
Net actuarial loss (gain)	347,799	557,564
Prior service gain	0	0
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os)	347,799	557,564	503,821
Income taxes (benefits)	(6,199)	(5,988)
AOCI debit/(credit), net of taxes (benefits) balance at the end of the period	17,438	16,982
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, balance at the beginning of the period	2,440,758	2,110,904
Service cost	79,463	71,604	60,461
Interest cost	70,235	75,484	77,851
Actuarial (gains) losses	(39,755)	260,102
Participants contributions	0	0
Benefits paid and expenses	(85,425)	(77,336)
Transfers	(332)	0
Benefit obligation, balance at the end of the period	2,464,944	2,440,758	2,110,904
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, balance at the beginning of the period	1,909,730	1,640,417
Actual return on plan assets	266,922	276,453
Employer contributions	51,079	69,720
Participants contributions	0	0
Benefits paid and expenses	(84,852)	(76,860)
Other	(262)	0
Fair value of plan assets, balance at the end of the period	2,142,617	1,909,730	1,640,417
Accrued benefit asset (liability), balance	(322,327)	(531,028)
Other assets	0	0
Other liabilities (short-term)	(547)	(535)
Defined benefit pension and other postretirement benefit plans liability	(321,780)	(530,493)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income [Roll Forward]
AOCI debit/(credit), balance at beginning of the period (excluding impact of PUC D&Os)	538,521	478,078
Recognized during year – prior service credit (cost)	0	(9)
Recognized during year – net actuarial loss	(27,534)	(30,566)
Occurring during year – net actuarial loss (gain)	(181,342)	91,018
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os)	329,645	538,521	478,078
Cumulative impact of PUC D&Os	(324,162)	(534,594)
AOCI debit/(credit), balance at end of the period	5,483	3,927
Net actuarial loss (gain)	329,645	538,521
Prior service gain	0	0
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os)	329,645	538,521	478,078
Income taxes (benefits)	(1,412)	(1,011)
AOCI debit/(credit), net of taxes (benefits) balance at the end of the period	4,071	2,916
Other benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, balance at the beginning of the period	226,421	215,639
Service cost	2,827	2,537	2,209
Interest cost	6,122	7,407	8,004
Actuarial (gains) losses	(8,527)	9,785
Participants contributions	2,943	2,768
Benefits paid and expenses	(11,635)	(11,715)
Benefit obligation, balance at the end of the period	218,151	226,421	215,639
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, balance at the beginning of the period	219,873	200,831
Actual return on plan assets	28,130	27,678
Employer contributions	0	0
Participants contributions	2,943	2,768
Benefits paid and expenses	(11,635)	(11,404)
Fair value of plan assets, balance at the end of the period	239,311	219,873	200,831
Accrued benefit asset (liability), balance	21,160	(6,548)
Other assets	21,663	0
Defined benefit pension and other postretirement benefit plans liability	(503)	(6,548)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income [Roll Forward]
AOCI debit/(credit), balance at beginning of the period (excluding impact of PUC D&Os)	2,395	6,610
Recognized during year – prior service credit (cost)	1,533	1,761
Recognized during year – net actuarial loss	(203)	(208)
Occurring during year – net actuarial loss (gain)	(23,700)	(5,768)
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os)	(19,975)	2,395	6,610
Cumulative impact of PUC D&Os	19,166	(1,177)
AOCI debit/(credit), balance at end of the period	(809)	1,218
Net actuarial loss (gain)	(18,172)	5,731
Prior service gain	(1,803)	(3,336)
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os)	(19,975)	2,395	6,610
Income taxes (benefits)	209	(313)
AOCI debit/(credit), net of taxes (benefits) balance at the end of the period	(600)	905
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, balance at the beginning of the period	217,074	207,073
Service cost	2,802	2,515	2,191
Interest cost	5,875	7,103	7,673
Actuarial (gains) losses	(7,779)	9,151
Participants contributions	2,886	2,717
Benefits paid and expenses	(11,388)	(11,485)
Transfers	0	0
Benefit obligation, balance at the end of the period	209,470	217,074	207,073
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, balance at the beginning of the period	216,315	197,564
Actual return on plan assets	27,712	27,207
Employer contributions	0	0
Participants contributions	2,886	2,717
Benefits paid and expenses	(11,388)	(11,173)
Other	0	0
Fair value of plan assets, balance at the end of the period	235,525	216,315	197,564
Accrued benefit asset (liability), balance	26,055	(759)
Other assets	26,055	0
Other liabilities (short-term)	0	(720)
Defined benefit pension and other postretirement benefit plans liability	0	(39)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income [Roll Forward]
AOCI debit/(credit), balance at beginning of the period (excluding impact of PUC D&Os)	1,181	5,730
Recognized during year – prior service credit (cost)	1,530	1,758
Recognized during year – net actuarial loss	(206)	(207)
Occurring during year – net actuarial loss (gain)	(22,736)	(6,100)
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os)	(20,231)	1,181	5,730
Cumulative impact of PUC D&Os	19,166	(1,177)
AOCI debit/(credit), balance at end of the period	(1,065)	4
Net actuarial loss (gain)	(18,434)	4,508
Prior service gain	(1,797)	(3,327)
AOCI debit/(credit), balance at end of the period (excluding impact of PUC D&Os)	(20,231)	1,181	$ 5,730
Income taxes (benefits)	274	(1)
AOCI debit/(credit), net of taxes (benefits) balance at the end of the period	$ (791)	$ 3