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Electric utility segment - Power purchase agreements (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Oct. 31, 2021 | Jul. 31, 2018 MW | May 31, 2012 MW | Mar. 31, 1988 MW | Sep. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) MW | Sep. 30, 2020 USD ($) | Dec. 31, 1988 MW
Kalaeloa | Subsequent Event |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchase commitment, extension period | 10 years |  |  |  |  |  |  |  |
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 |  |  |  |  |  |
Molokai New Energy Partners |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Total contracted PV capacity (in megawatts) | MW |  | 4.88 |  |  |  |  |  |  |
Total contracted battery energy storage system capacity | MW |  | 3 |  |  |  |  |  |  |
Maximum power volume to be delivered (in megawatts) | MW |  | 2.64 |  |  |  |  |  |  |
Hawaiian Electric, Parent |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchased power |  |  |  |  | $ 186 | $ 149 | $ 491 | $ 426 |
Hawaiian Electric, Parent | Kalaeloa |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchased power |  |  |  |  | 56 | 39 | 142 | 111 |
Increased power purchase commitment capacity (in megawatts) | MW |  |  |  |  |  |  |  |  | 208
Hawaiian Electric, Parent | AES Hawaii |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchased power |  |  |  |  | 32 | 33 | 98 | 96 |
Hawaiian Electric, Parent | HPOWER |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchased power |  |  |  |  | 20 | 18 | 51 | 52 |
Hawaiian Electric, Parent | Hamakua Energy |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchased power |  |  |  |  | 15 | 12 | 38 | 36 |
Hawaiian Electric, Parent | Puna Geothermal Venture |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchased power |  |  |  |  | 9 | 0 | 20 | 0 |
Hawaiian Electric, Parent | Wind IPPs |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchased power |  |  |  |  | 38 | 30 | 95 | 83 |
Hawaiian Electric, Parent | Solar IPPs |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchased power |  |  |  |  | 12 | 17 | 40 | 45 |
Hawaiian Electric, Parent | Other IPPs |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |
Purchased power |  |  |  |  | $ 4 | $ 0 | $ 7 | $ 3 |

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