Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 2,303,642	$ 2,390,884	$ 2,321,293	$ 2,337,502	$ 2,390,884	$ 2,337,502
Current period other comprehensive income (loss)	(87,840)	(117,159)	16,472	(44,016)	(204,999)	(27,544)
Ending balance	2,233,504	2,303,642	2,367,329	2,321,293	2,233,504	2,367,329
AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(169,692)	(52,533)	(45,280)	(1,264)	(52,533)	(1,264)
Current period other comprehensive income (loss)	(87,840)	(117,159)	16,472	(44,016)
Ending balance	(257,532)	(169,692)	(28,808)	(45,280)	(257,532)	(28,808)
Net unrealized gains (losses) on securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(32,037)		19,986	(32,037)	19,986
Current period other comprehensive income (loss)					(209,264)	(28,801)
Ending balance	(241,301)		(8,815)		(241,301)	(8,815)
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(3,638)		(3,363)	(3,638)	(3,363)
Current period other comprehensive income (loss)					3,911	861
Ending balance	273		(2,502)		273	(2,502)
Retirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(16,858)		(17,887)	(16,858)	(17,887)
Current period other comprehensive income (loss)					354	396
Ending balance	(16,504)		(17,491)		(16,504)	(17,491)
Hawaiian Electric Company, Inc. and Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	2,276,884	2,261,899	2,157,385	2,141,918	2,261,899	2,141,918
Current period other comprehensive income (loss)	51	51	35	34	102	69
Ending balance	2,289,595	2,276,884	2,171,396	2,157,385	2,289,595	2,171,396
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3,229)	(3,280)	(2,885)	(2,919)	(3,280)	(2,919)
Current period other comprehensive income (loss)	51	51	35	34
Ending balance	(3,178)	(3,229)	(2,850)	(2,885)	(3,178)	(2,850)
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ (3,280)		$ (2,919)	(3,280)	(2,919)
Current period other comprehensive income (loss)					102	69
Ending balance	$ (3,178)		$ (2,850)		$ (3,178)	$ (2,850)