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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 |  |  |  |  |

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