Electric utility segment - Commitments and contingencies (Details)					1 Months Ended							12 Months Ended	26 Months Ended	27 Months Ended	37 Months Ended
	Jun. 07, 2018 USD ($)	Aug. 11, 2016 USD ($)	May 23, 2016	Jan. 05, 2016 USD ($)	Jun. 30, 2017 $ / kWh	Jul. 31, 2016 MW	Sep. 30, 2015	Jun. 30, 2015 MW	Aug. 31, 2012 MW	May 31, 2012 MW	Mar. 31, 1988 MW	Dec. 31, 1988 MW	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)
Regulatory Projects and Legal Obligations [Line Items]
Power purchase agreement, termination period			60 days
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		1.75%
ERP/EAM implementation project costs													$ 73,300,000
ERP/EAM implementation project, operations and management													12,900,000
ERP/EAM implementation project, capital costs													2,600,000
ERP/EAM implementation project, deferred costs													57,800,000
Schofield generating station facility capacity (in megawatts) | MW									50
Project lease term (in years)				35 years
Schofield generating station project, budgetary cap				$ 157,300,000
Effective amount recoverable through MPIR													141,600,000	$ 141,600,000	$ 141,600,000
Percent of costs recoverable through recovery mechanisms other than base rates							90.00%
Annualized operation and maintenance expense	$ 1,800,000
Project cost incurred															142,500,000
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														28,600,000
Accounts receivable and unbilled revenues, net													336,309,000	336,309,000	336,309,000	$ 263,209,000
PCB Contamination
Environmental regulation
Valuation allowances and reserves													4,600,000	4,600,000	4,600,000
AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchase commitment, period (in years)											30 years
Minimum power volume required (in megawatts) | MW									186		180
Additional capacity requirement (in megawatts) | MW								9
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													17,400,000	17,400,000	17,400,000
Hawaiian Electric (parent only) | Hawaiian Telcom
Regulatory Projects and Legal Obligations [Line Items]
Accounts receivable and unbilled revenues, net													11,600,000	11,600,000	11,600,000
Hawaiian Telcom
Regulatory Projects and Legal Obligations [Line Items]
Accounts receivable and unbilled revenues, net													48,000,000	48,000,000	48,000,000
Hawaii Electric Light Company, Inc. (HELCO) | Hawaiian Telcom
Regulatory Projects and Legal Obligations [Line Items]
Accounts receivable and unbilled revenues, net													4,700,000	4,700,000	4,700,000
Maui Electric
Environmental regulation
Additional accrued investigation and estimated cleanup costs													2,700,000	2,700,000	2,700,000
Maui Electric | Hawaiian Telcom
Regulatory Projects and Legal Obligations [Line Items]
Accounts receivable and unbilled revenues, net													$ 1,100,000	$ 1,100,000	$ 1,100,000
Kalaeloa Partners, L.P. (Kalaeloa) | Hawaiian Electric (parent only)
Regulatory Projects and Legal Obligations [Line Items]
Increased power purchase commitment capacity (in megawatts) | MW												208