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Income taxes - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Changes in total unrecognized tax benefits |  |  |
Unrecognized tax benefits, at the beginning of the period | $ 12.7 | $ 2.2 | $ 2.1
Additions based on tax positions taken during the year | 2.8 | 0.2 | 0.5
Reductions based on tax positions taken during the year | (0.5) | 0.0 | 0.0
Additions for tax positions of prior years | 7.6 | 11.6 | 0.1
Reductions for tax positions of prior years | (5.5) | (0.1) | (0.2)
Lapses of statute of limitations | 0.0 | (0.2) | (0.3)
Settlement | 0.0 | (1.0) | 0.0
Unrecognized tax benefits, at the end of the period | 17.1 | 12.7 | 2.2
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Changes in total unrecognized tax benefits |  |  |
Unrecognized tax benefits, at the beginning of the period | 12.7 | 1.7 | 1.6
Additions based on tax positions taken during the year | 0.3 | 0.2 | 0.5
Reductions based on tax positions taken during the year | 0.0 | 0.0 | 0.0
Additions for tax positions of prior years | 0.2 | 11.6 | 0.1
Reductions for tax positions of prior years | (1.6) | (0.1) | (0.2)
Lapses of statute of limitations | 0.0 | (0.2) | (0.3)
Settlement | 0.0 | (0.5) | 0.0
Unrecognized tax benefits, at the end of the period | $ 11.6 | $ 12.7 | $ 1.7

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