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Income taxes - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Changes in total unrecognized tax benefits |  |  |
Unrecognized tax benefits, at the beginning of the period | $ 17.1 | $ 12.7 | $ 2.2
Additions based on tax positions taken during the year | 19.0 | 2.8 | 0.2
Reductions based on tax positions taken during the year | (3.5) | (0.5) | 0.0
Additions for tax positions of prior years | 0.6 | 7.6 | 11.6
Reductions for tax positions of prior years | (2.6) | (5.5) | (0.1)
Lapses of statute of limitations | 0.0 | 0.0 | (0.2)
Settlement | 0.0 | 0.0 | (1.0)
Unrecognized tax benefits, at the end of the period | 30.6 | 17.1 | 12.7
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Changes in total unrecognized tax benefits |  |  |
Unrecognized tax benefits, at the beginning of the period | 11.6 | 12.7 | 1.7
Additions based on tax positions taken during the year | 0.1 | 0.3 | 0.2
Reductions based on tax positions taken during the year | 0.0 | 0.0 | 0.0
Additions for tax positions of prior years | 0.2 | 0.2 | 11.6
Reductions for tax positions of prior years | (0.2) | (1.6) | (0.1)
Lapses of statute of limitations | 0.0 | 0.0 | (0.2)
Settlement | 0.0 | 0.0 | (0.5)
Unrecognized tax benefits, at the end of the period | $ 11.7 | $ 11.6 | $ 12.7

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