Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance		$ 2,280,260	$ 2,183,515	$ 2,162,280	$ 2,280,260	$ 2,162,280
Current period other comprehensive income (loss)	$ (332)	18,212	13,699	9,241	17,880	22,940
Ending Balance	2,291,398		2,208,586	2,183,515	2,291,398	2,208,586
AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance		(20,039)	(41,369)	(50,610)	(20,039)	(50,610)
Current period other comprehensive income (loss)	(332)	18,212	13,699	9,241	17,880	22,940
Ending Balance	(2,159)		(27,670)	(41,369)	(2,159)	(27,670)
Net unrealized gains (losses) on securities
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance		2,481		(24,423)	2,481	(24,423)
Current period other comprehensive income (loss)					18,783	23,593
Ending Balance	21,264		(830)		21,264	(830)
Unrealized gains (losses) on derivatives
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance		(1,613)		(436)	(1,613)	(436)
Current period other comprehensive income (loss)					(1,982)	(1,063)
Ending Balance	(3,595)		(1,499)		(3,595)	(1,499)
Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance		(20,907)		(25,751)	(20,907)	(25,751)
Current period other comprehensive income (loss)					1,079	410
Ending Balance	(19,828)		(25,341)		(19,828)	(25,341)
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	2,044,499	2,047,352	1,964,478	1,957,641	2,047,352	1,957,641
Current period other comprehensive income (loss)	25	26	23	24	51	47
Ending Balance	2,060,069	2,044,499	1,971,762	1,964,478	2,060,069	1,971,762
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(1,253)	(1,279)	123	99	(1,279)	99
Current period other comprehensive income (loss)	25	26	23	24
Ending Balance	(1,228)	(1,253)	146	123	(1,228)	146
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance		$ (1,279)		$ 99	(1,279)	99
Current period other comprehensive income (loss)					51	47
Ending Balance	$ (1,228)		$ 146		$ (1,228)	$ 146