Retirement benefits - Components of NPBC (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension benefits
Defined benefit plans
Service cost	$ 60,555	$ 66,260	$ 49,264
Interest cost	81,549	76,960	72,202
Expected return on plan assets	(98,559)	(88,554)	(81,355)
Amortization of net prior service (gain) cost	(57)	4	88
Amortization of net actuarial loss (gain)	24,832	36,800	20,304
Net periodic pension/benefit cost	68,320	91,470	60,503
Impact of PUC D&Os	(18,117)	(40,011)	(13,324)
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	50,203	51,459	47,179
Amounts amortized from AOCI or regulatory assets into net periodic pension benefit cost during 2015
Prior service credit	(100)
Net actuarial loss	26,100
Defined benefit plans - ABOs	1,700,000	1,600,000
Aggregate accumulated benefit obligations	1,600,000	1,500,000
Plan assets	1,300,000	1,200,000
Aggregate projected benefit obligations	1,800,000	1,700,000
Plan assets	1,300,000	1,200,000
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Service cost	58,796	64,262	47,597
Interest cost	74,808	70,529	65,979
Expected return on plan assets	(91,633)	(82,541)	(72,661)
Amortization of net prior service (gain) cost	13	40	62
Amortization of net actuarial loss (gain)	22,693	33,371	18,459
Net periodic pension/benefit cost	64,677	85,661	59,436
Impact of PUC D&Os	(18,117)	(40,011)	(13,324)
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	46,560	45,650	46,112
Amounts amortized from AOCI or regulatory assets into net periodic pension benefit cost during 2015
Prior service credit	0
Net actuarial loss	24,000
Defined benefit plans - ABOs	1,500,000	1,400,000
Aggregate accumulated benefit obligations	1,500,000	1,400,000
Plan assets	1,200,000	1,100,000
Aggregate projected benefit obligations	1,800,000	1,600,000
Plan assets	1,200,000	1,100,000
Other benefits
Defined benefit plans
Service cost	3,331	3,927	3,490
Interest cost	9,670	9,011	8,550
Expected return on plan assets	(12,273)	(11,664)	(10,902)
Amortization of net prior service (gain) cost	(1,793)	(1,793)	(1,793)
Amortization of net actuarial loss (gain)	804	1,796	(11)
Net periodic pension/benefit cost	(261)	1,277	(666)
Impact of PUC D&Os	1,343	(240)	1,976
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	1,082	1,037	1,310
Amounts amortized from AOCI or regulatory assets into net periodic pension benefit cost during 2015
Prior service credit	(1,800)
Net actuarial loss	1,500
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans
Service cost	3,284	3,870	3,392
Interest cost	9,337	8,700	8,234
Expected return on plan assets	(12,096)	(11,495)	(10,739)
Amortization of net prior service (gain) cost	(1,803)	(1,804)	(1,804)
Amortization of net actuarial loss (gain)	793	1,754	0
Net periodic pension/benefit cost	(485)	1,025	(917)
Impact of PUC D&Os	1,343	(240)	1,976
Net periodic pension/benefit cost (adjusted for impact of PUC D&Os)	858	$ 785	$ 1,059
Amounts amortized from AOCI or regulatory assets into net periodic pension benefit cost during 2015
Prior service credit	(1,800)
Net actuarial loss	$ 1,400