Shareholders' equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 1,534,432	$ 1,505,876	$ 1,479,089	$ 1,085,273	$ 2,377,380	$ 2,344,841	$ 1,479,089	$ 2,344,841
Current period other comprehensive income (loss)	(734)	(306)	(460)	39,360	1,594	(9,801)	(1,500)	31,153
Ending balance	1,563,836	1,534,432	1,505,876	1,577,041	1,085,273	2,377,380	1,563,836	1,577,041
AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	2,695	3,001	3,461	(297,557)	(299,151)	(289,350)	3,461	(289,350)
Current period other comprehensive income (loss)	(734)	(306)	(460)	39,360	1,594	(9,801)
Ending balance	1,961	2,695	3,001	(258,197)	(297,557)	(299,151)	1,961	(258,197)
Net unrealized gains (losses) on securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			0			(282,963)	0	(282,963)
Current period other comprehensive income (loss)							0	31,260
Ending balance	0			(251,703)			0	(251,703)
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			2,120			1,638	2,120	1,638
Current period other comprehensive income (loss)							(1,466)	(220)
Ending balance	654			1,418			654	1,418
Retirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			1,341			(8,025)	1,341	(8,025)
Current period other comprehensive income (loss)							(34)	113
Ending balance	1,307			(7,912)			1,307	(7,912)
Hawaiian Electric Company, Inc. and Subsidiaries
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1,521,617	1,492,244	1,156,955	1,192,842	2,435,282	2,409,110	1,156,955	2,409,110
Current period other comprehensive income (loss)	(24)	(47)	(47)	2	(46)	(49)	(118)	(93)
Ending balance	1,548,581	1,521,617	1,492,244	1,110,259	1,192,842	2,435,282	1,548,581	1,110,259
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	2,692	2,739	2,786	2,754	2,800	2,849	2,786	2,849
Current period other comprehensive income (loss)	(24)	(47)	(47)	2	(46)	(49)
Ending balance	2,668	$ 2,692	2,739	2,756	$ 2,754	2,800	2,668	2,756
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 2,786			$ 2,849	2,786	2,849
Current period other comprehensive income (loss)							(118)	(93)
Ending balance	$ 2,668			$ 2,756			$ 2,668	$ 2,756