Retirement benefits - Components of NPPC and NPBC (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension benefits
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 73,387	$ 62,135	$ 68,987
Interest cost	81,335	84,267	77,374
Expected return on plan assets	(113,800)	(111,989)	(108,953)
Amortization of net prior service gain	8	(42)	(42)
Amortization of net actuarial losses	33,456	15,479	30,084
Net periodic pension/benefit cost	74,386	49,850	67,450
Impact of PUC D&Os	20,997	48,143	25,828
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	95,383	97,993	93,278
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	71,604	60,461	67,359
Interest cost	75,484	77,851	71,294
Expected return on plan assets	(107,369)	(104,632)	(102,368)
Amortization of net prior service gain	9	7	8
Amortization of net actuarial losses	30,566	14,658	27,302
Net periodic pension/benefit cost	70,294	48,345	63,595
Impact of PUC D&Os	20,997	48,143	25,828
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	91,291	96,488	89,423
Other benefits
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	2,537	2,209	2,721
Interest cost	7,407	8,004	7,933
Expected return on plan assets	(12,124)	(12,356)	(12,908)
Amortization of net prior service gain	(1,761)	(1,806)	(1,805)
Amortization of net actuarial losses	208	(13)	95
Net periodic pension/benefit cost	(3,733)	(3,962)	(3,964)
Impact of PUC D&Os	3,179	3,258	3,842
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	(554)	(704)	(122)
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	2,515	2,191	2,704
Interest cost	7,103	7,673	7,628
Expected return on plan assets	(11,957)	(12,180)	(12,713)
Amortization of net prior service gain	(1,758)	(1,803)	(1,803)
Amortization of net actuarial losses	207	0	98
Net periodic pension/benefit cost	(3,890)	(4,119)	(4,086)
Impact of PUC D&Os	3,179	3,258	3,842
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	$ (711)	$ (861)	$ (244)