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Retirement benefits - Narrative (Details) - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2024 | Jun. 30, 2023
Retirement benefits |  |
Contributions made to defined benefit plans | $ 3.0 | $ 4.0
Contributions expected to be paid in current year | 8.0 |
Expected payments for remainder of fiscal year | 3.0 |
Retirement benefits expense | $ 23.0 | 22.0
Number of years for which regulatory asset/liability for each utility will be amortized, beginning with respective utility's next rate case (in years) | 5 years |
Defined contribution plan, expenses recognized | $ 5.8 | 4.2
Cash contributions by the employer to defined contribution plan | 5.8 | 5.0
Hawaiian Electric Company, Inc. and Subsidiaries |  |
Retirement benefits |  |
Contributions made to defined benefit plans | 3.0 | 4.0
Contributions expected to be paid in current year | 8.0 |
Expected payments for remainder of fiscal year | 1.0 |
Retirement benefits expense | 23.0 | 22.0
Defined contribution plan, expenses recognized | 3.5 | 2.6
Cash contributions by the employer to defined contribution plan | $ 3.5 | $ 2.6

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