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Electric utility segment - Utility projects (Details) - USD ($) $ in Millions |  | 3 Months Ended |
--- | --- | --- | ---
Jun. 10, 2019 | Mar. 31, 2022 | Oct. 31, 2018
ERP/EAM Implementation Project |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
ERP/EAM project service period (in years) | 12 years |  |
Future O&M expense reductions | $ 150.0 |  |
Future cost avoidance related to capital cost and tax costs | $ 96.0 |  |
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
Regulatory liability for O&M expense reductions |  | $ 9.1 |
Hawaiian Electric, Parent | PCB Contamination |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Valuation allowances and reserves |  | 10.1 |
Hawaiian Electric, Parent | ERP/EAM Implementation Project |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory liability for O&M expense reductions |  | 5.1 |
HELCO | ERP/EAM Implementation Project |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory liability for O&M expense reductions |  | 1.6 |
Maui Electric |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Additional accrued investigation and estimated cleanup costs |  | 2.7 |
Maui Electric | ERP/EAM Implementation Project |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory liability for O&M expense reductions |  | $ 2.4 |
Regulatory liability, amortization period |  | 5 years |

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