Shareholders' equity - Accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	$ 2,291,398		$ 2,280,260	$ 2,208,586	$ 2,183,515	$ 2,162,280	$ 2,280,260	$ 2,162,280
Current period other comprehensive income (loss)	1,440	$ (332)	18,212	3,297	13,699	9,241	19,320	26,237
Ending Balance	2,323,231	2,291,398		2,242,689	2,208,586	2,183,515	2,323,231	2,242,689
AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(2,159)		(20,039)	(27,670)	(41,369)	(50,610)	(20,039)	(50,610)
Current period other comprehensive income (loss)	1,440	(332)	18,212	3,297	13,699	9,241	19,320	26,237
Ending Balance	(719)	(2,159)		(24,373)	(27,670)	(41,369)	(719)	(24,373)
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)							19,767	27,368
Ending Balance	22,248			2,945			22,248	2,945
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)							(2,129)	(1,663)
Ending Balance	(3,742)			(2,099)			(3,742)	(2,099)
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)							1,682	532
Ending Balance	(19,225)			(25,219)			(19,225)	(25,219)
Hawaiian Electric Company, Inc. and Subsidiaries
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	2,060,069	2,044,499	2,047,352	1,971,762	1,964,478	1,957,641	2,047,352	1,957,641
Current period other comprehensive income (loss)	48	25	26	26	23	24	99	73
Ending Balance	2,093,398	2,060,069	2,044,499	1,993,254	1,971,762	1,964,478	2,093,398	1,993,254
Hawaiian Electric Company, Inc. and Subsidiaries | AOCI
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Beginning Balance	(1,228)	(1,253)	(1,279)	146	123	99	(1,279)	99
Current period other comprehensive income (loss)	48	25	26	26	23	24
Ending Balance	(1,180)	$ (1,228)	(1,253)	172	$ 146	123	(1,180)	172
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)							99	73
Ending Balance	$ (1,180)			$ 172			$ (1,180)	$ 172