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Electric utility segment - Utility Projects (Details) $ in Millions |  | 1 Months Ended | 3 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Jan. 31, 2024 USD ($) | Sep. 30, 2020 MW | Mar. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Aug. 29, 2023 USD ($) | Nov. 30, 2021 USD ($) | Oct. 31, 2020 transmission_line generationUnit kV
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Public utilities, project cost recovery cap |  |  |  |  | $ 95.0 |  |
Project costs incurred |  |  | $ 1.5 |  |  |  |
Waena Switchyard/Synchronous Condenser Project | Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Number of extended transmission lines | transmission_line |  |  |  |  |  |  | 2
Number of kilovolts | kV |  |  |  |  |  |  | 69
Number of generating units converting to synchronous condensers | generationUnit |  |  |  |  |  |  | 2
Renewable energy generation project, approved funds |  |  |  |  |  | $ 38.8 |
Renewable energy generation project, incurred cost |  |  | 25.3 |  |  |  |
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 |  |  | $ 0.6 |  |  |  |
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 | 5 years |  |  |  |  |  |

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