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Electric utility segment - Utility Projects (Details) $ in Millions |  | 1 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | ---
Jan. 31, 2024 USD ($) | Jul. 31, 2025 | Sep. 30, 2020 MW | Jun. 30, 2025 USD ($) | Aug. 07, 2024 USD ($) | Dec. 31, 2023 USD ($)
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public utilities, project cost recovery cap |  |  |  |  | $ 95.0 |
Project costs incurred |  |  |  | $ 27.0 |  |
Waena Battery Energy Storage System Project |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Total contracted battery energy storage system capacity | MW |  |  | 40 |  |  |
Waena Battery Energy Storage System Project | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Renewable energy generation project, approved funds |  |  |  |  |  | $ 82.1
Renewable energy generation project, incurred cost |  |  |  | $ 9.7 |  |
Waena Battery Energy Storage System Project | Hawaiian Electric Company, Inc. and Subsidiaries | Subsequent Event |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public utilities, approved estimated capital costs (as percent) |  | 20.00% |  |  |  |
Climate Adaptation Transmission And Distribution Resilience Program | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Public utilities, electric grid project, approved funds | $ 189.7 |  |  |  |  |
Project period (in years) | 5 years |  |  |  |  |

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