Electric utility segment - Commitments and contingencies (Details)									1 Months Ended										3 Months Ended	9 Months Ended	14 Months Ended	15 Months Ended	25 Months Ended
	Oct. 12, 2017 USD ($)	Aug. 21, 2017 USD ($)	Jul. 11, 2017	Dec. 16, 2016 USD ($)	Sep. 19, 2016 USD ($)	Aug. 11, 2016 USD ($)	Aug. 01, 2016	Jan. 05, 2016 USD ($)	Jun. 30, 2017 USD ($) $ / kWh	May 31, 2017 USD ($)	Jul. 31, 2016 MW	Sep. 30, 2015 USD ($)	Jun. 30, 2015 MW	Aug. 31, 2012 MW	May 31, 2012 MW	Oct. 31, 2004 MW	Oct. 31, 1988 MW	Mar. 31, 1988 MW	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)
Regulatory Projects and Legal Obligations [Line Items]
Power purchase agreement, termination period							60 days
Purchase commitment, period (in years)																		30 years
Minimum power volume required (in megawatts) | MW														186				180
Additional capacity requirement (in megawatts) | MW													9
ERP/EAM cost recovery cap						$ 77,600,000
Public utility, ERP/EAM required pass through savings to customers						$ 244,000,000
ERP/EAM project service period (in years)						12 years
AFUDC rate (as a percent)						1.75%
ERP/EAM implementation project costs																					$ 23,600,000
ERP/EAM implementation project, operations and management																					4,600,000
ERP/EAM implementation project, capital costs																					1,400,000
ERP/EAM implementation project, deferred costs																					17,600,000
Schofield generating station facility capacity (in megawatts) | MW														50
Schofield generating station project, budgetary cap								$ 157,300,000				$ 167,000,000
Percent of costs recoverable through recovery mechanisms other than base rates (as a percent)												90.00%
Decrease in project costs								$ 9,700,000
Project lease term (in years)								35 years
Project cost incurred																							$ 105,700,000
West Lock PV Project, energy generated (in megawatts) | MW											20
West Lock PV Project, cost cap									$ 67,000,000
West Lock PV Project, maximum energy cost (in dollars per kilowatt hours) | $ / kWh									0.0956
West Lock PV Project, project costs incurred																						$ 700,000
Accounts receivable and unbilled revenues, net																			$ 264,426,000	$ 264,426,000	264,426,000	264,426,000	264,426,000	$ 237,950,000
Environmental regulation
Decoupling order, service reliability performance, historical measurement period (in years)										10 years
Maximum penalty as a percent of equity (as a percent)										0.20%
Service reliability, maximum penalty										$ 6,000,000
Dead band percentage above or below the target (as a percent)										3.00%
Maximum incentive, percent of return on equity (as a percent)										0.08%
Call center performance, maximum penalty										$ 1,200,000
Threshold of capital expenditures in excess of customer contributions for qualification for major project interim recovery										$ 2,500,000.0
General rate increase, revenue				$ 106,400,000
General rate increase, revenue, percent				6.90%
General rate increase, revenue, calculation assumptions, rate of return				8.28%
General rate increase, revenue, calculation assumptions, rate of return, ROACE				10.60%
General rate increase, revenue, calculation assumptions, rate of return, common equity capitalization percentage				57.40%
General rate increase, revenue, calculation assumptions, rate base				$ 2,000,000,000.0
Requirement for application for general rate case (in years)																				3 years
PCB Contamination
Environmental regulation
Valuation allowances and reserves																			4,900,000	$ 4,900,000	4,900,000	4,900,000	4,900,000
Hu Honua Bioenergy, LLC
Regulatory Projects and Legal Obligations [Line Items]
Minimum power volume required (in megawatts) | MW															21.5
Hawaiian Telcom
Regulatory Projects and Legal Obligations [Line Items]
Accounts receivable and unbilled revenues, net																			22,200,000	22,200,000	22,200,000	22,200,000	22,200,000
Reserve for interest accrued																			4,900,000	4,900,000	4,900,000	4,900,000	4,900,000
Hawaiian Electric Company | Hawaiian Telcom
Regulatory Projects and Legal Obligations [Line Items]
Accounts receivable and unbilled revenues, net																			14,900,000	14,900,000	14,900,000	14,900,000	14,900,000
Hawaii Electric Light Company, Inc. (HELCO)
Environmental regulation
General rate increase, revenue					$ 19,300,000
General rate increase, revenue, percent					6.50%
General rate increase, revenue, calculation assumptions, rate of return					8.44%
General rate increase, revenue, calculation assumptions, rate of return, ROACE					10.60%
General rate increase, ROACE, percentage decrease			0.25%
Stipulated ROACE rate		9.50%	9.75%
Interim general rate increase granted		$ 9,900,000
Hawaii Electric Light Company, Inc. (HELCO) | Hawaiian Telcom
Regulatory Projects and Legal Obligations [Line Items]
Accounts receivable and unbilled revenues, net																			6,000,000	6,000,000	6,000,000	6,000,000	6,000,000
Maui Electric
Environmental regulation
Additional accrued investigation and estimated cleanup costs																			3,100,000	3,100,000	3,100,000	3,100,000	3,100,000
Maui Electric | Subsequent Event
Environmental regulation
General rate increase, revenue	$ 30,100,000
General rate increase, revenue, percent	9.30%
General rate increase, revenue, calculation assumptions, rate of return	8.05%
General rate increase, revenue, calculation assumptions, rate of return, ROACE	10.60%
General rate increase, revenue, calculation assumptions, rate of return, common equity capitalization percentage	56.90%
General rate increase, revenue, calculation assumptions, rate base	$ 473,000,000
Conditional general rate increase, revenue	$ 46,600,000
Conditional general rate increase, revenue, percentage	14.30%
Maui Electric | Hawaiian Telcom
Regulatory Projects and Legal Obligations [Line Items]
Accounts receivable and unbilled revenues, net																			1,300,000	1,300,000	1,300,000	1,300,000	1,300,000
Hawaiian Electric Company, Inc. and Subsidiaries
Environmental regulation
Reversal of asset retirement obligations																			24,400,000
Asset retirement obligation																			$ 700,000	$ 700,000	$ 700,000	$ 700,000	$ 700,000		$ 26,200,000
Kalaeloa Partners, L.P. (Kalaeloa) | Hawaiian Electric Company
Regulatory Projects and Legal Obligations [Line Items]
Power purchase capacity that Increases from initial capacity (in megawatts) | MW																	180
Power purchase agreement term																	25 years
Increased power purchase commitment capacity (in megawatts) | MW																208