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Retirement benefits - Narrative (Details) - USD ($) $ in Millions | 9 Months Ended
--- | ---
Sep. 30, 2025 | Sep. 30, 2024
Retirement benefits |  |
Contributions made to defined benefit plans | $ 6.0 | $ 5.0
Contributions expected to be paid in current year | 12.0 | 9.0
Expected payments for remainder of fiscal year | 3.0 | 2.0
Retirement benefits expense | $ 35.0 |
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 | $ 6.2 | 5.7
Cash contributions by the employer to defined contribution plan | 6.2 | 5.7
Hawaiian Electric Company, Inc. and Subsidiaries |  |
Retirement benefits |  |
Contributions made to defined benefit plans | 6.0 | 5.0
Contributions expected to be paid in current year | 11.0 | 9.0
Expected payments for remainder of fiscal year | 1.0 | 1.0
Retirement benefits expense | 34.0 |
Defined contribution plan, expenses recognized | 5.9 | 5.5
Cash contributions by the employer to defined contribution plan | $ 5.9 | $ 5.5

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