Retirement benefits - Components of NPPC and NPBC (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension benefits
Defined benefit plans
Service cost	$ 62,135	$ 68,987	$ 64,906
Interest cost	84,267	77,374	81,185
Expected return on plan assets	(111,989)	(108,953)	(102,745)
Amortization of net prior service gain	(42)	(42)	(55)
Amortization of net actuarial losses	15,479	30,084	26,496
Net periodic pension/benefit cost	49,850	67,450	69,787
Impact of PUC D&Os	48,143	25,828	(18,004)
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	97,993	93,278	51,783
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Service cost	60,461	67,359	63,059
Interest cost	77,851	71,294	74,632
Expected return on plan assets	(104,632)	(102,368)	(95,892)
Amortization of net prior service gain	7	8	8
Amortization of net actuarial losses	14,658	27,302	24,392
Net periodic pension/benefit cost	48,345	63,595	66,199
Impact of PUC D&Os	48,143	25,828	(18,004)
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	96,488	89,423	48,195
Other benefits
Defined benefit plans
Service cost	2,209	2,721	3,374
Interest cost	8,004	7,933	9,453
Expected return on plan assets	(12,356)	(12,908)	(12,326)
Amortization of net prior service gain	(1,806)	(1,805)	(1,793)
Amortization of net actuarial losses	(13)	95	1,130
Net periodic pension/benefit cost	(3,962)	(3,964)	(162)
Impact of PUC D&Os	3,258	3,842	1,211
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	(704)	(122)	1,049
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Service cost	2,191	2,704	3,353
Interest cost	7,673	7,628	9,115
Expected return on plan assets	(12,180)	(12,713)	(12,147)
Amortization of net prior service gain	(1,803)	(1,803)	(1,804)
Amortization of net actuarial losses	0	98	1,102
Net periodic pension/benefit cost	(4,119)	(4,086)	(381)
Impact of PUC D&Os	3,258	3,842	1,211
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	$ (861)	$ (244)	$ 830