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Electric utility segment - Commitments and contingencies (Details) |  | 1 Months Ended | 12 Months Ended | 36 Months Ended |
--- | --- | --- | --- | --- | ---
Aug. 11, 2016 | Jun. 30, 2017 USD ($) $ / kWh MW | Jun. 30, 2015 MW | May 31, 2012 MW | Mar. 31, 1988 MW | Dec. 31, 1988 MW | Jun. 30, 2019 USD ($) | Jun. 10, 2019 USD ($)
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |
AFUDC rate | 1.75% |  |  |  |  |  |  |
Project costs, accrued carrying costs once put into service |  |  |  |  |  |  | $ 58,900,000 |
Future O&M expense reductions |  |  |  |  |  |  |  | $ 150,000,000
Future cost avoidance related to capital cost and tax costs |  |  |  |  |  |  |  | $ 96,000,000
ERP/EAM project service period (in years) | 12 years |  |  |  |  |  |  |
Regulatory liability for O&M expense reductions |  |  |  |  |  |  | 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 |  |  |  |  |  |  | 46,500,000 |
PCB Contamination |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |
Valuation allowances and reserves |  |  |  |  |  |  | 4,700,000 |
AES Hawaii |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |
Purchase commitment, period (in years) |  |  |  |  | 30 years |  |  |
Minimum power volume required (in megawatts) | MW |  |  |  |  | 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 |  |  |  |
Maui Electric |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |
Additional accrued investigation and estimated cleanup costs |  |  |  |  |  |  | $ 2,700,000 |
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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