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Electric utility segment - Utility projects (Details) $ in Millions | 3 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Mar. 31, 2023 USD ($) | Nov. 30, 2021 USD ($) | Oct. 31, 2020 generationUnit transmission_line kV | Jun. 10, 2019 USD ($) | Oct. 31, 2018 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Environmental loss contingency, statement of financial position, not disclosed | reserve account balance |  |  |  |
Hawaiian Electric Company, Inc. and Subsidiaries | ERP/EAM Implementation Project |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
ERP/EAM project service period (in years) | 12 years |  |  |  |
ERP/EAM project service, savings over 12 years |  |  |  |  | $ 246.0
Future O&M expense reductions |  |  |  | $ 150.0 |
Future cost avoidance related to capital cost and tax costs |  |  |  | $ 96.0 |
Regulatory liability for O&M expense reductions | $ 11.0 |  |  |  |
Hawaiian Electric Company, Inc. and Subsidiaries | Waena Switchyard/Synchronous Condenser Project |  |  |  |  |
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 | 17.1 |  |  |  |
Hawaiian Electric, Parent | PCB Contamination |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Valuation allowances and reserves | 9.9 |  |  |  |
Hawaiian Electric, Parent | ERP/EAM Implementation Project |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Regulatory liability for O&M expense reductions | 3.7 |  |  |  |
Hawaii Electric Light Company, Inc | ERP/EAM Implementation Project |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Regulatory liability for O&M expense reductions | 2.9 |  |  |  |
Maui Electric |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Additional accrued investigation and estimated cleanup costs | 2.6 |  |  |  |
Maui Electric | ERP/EAM Implementation Project |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Regulatory liability for O&M expense reductions | $ 4.4 |  |  |  |
Regulatory liability, amortization period | 5 years |  |  |  |

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