Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 2,390,884	$ 2,337,502
Current period other comprehensive income (loss)	(117,159)	(44,016)
Ending balance	2,303,642	2,321,293
AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(52,533)	(1,264)
Current period other comprehensive income (loss)	(117,159)	(44,016)
Ending balance	(169,692)	(45,280)
Net unrealized gains (losses) on securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(32,037)	19,986
Current period other comprehensive income (loss)	(120,407)	(45,777)
Ending balance	(152,444)	(25,791)
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,638)	(3,363)
Current period other comprehensive income (loss)	3,072	1,562
Ending balance	(566)	(1,801)
Retirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(16,858)	(17,887)
Current period other comprehensive income (loss)	176	199
Ending balance	(16,682)	(17,688)
Hawaiian Electric Company, Inc. and Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	2,261,899	2,141,918
Current period other comprehensive income (loss)	51	34
Ending balance	2,276,884	2,157,385
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,280)	(2,919)
Current period other comprehensive income (loss)	51	34
Ending balance	(3,229)	(2,885)
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,280)	(2,919)
Current period other comprehensive income (loss)	51	34
Ending balance	$ (3,229)	$ (2,885)