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Summary of significant accounting policies (Tables) | 12 Months Ended
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Dec. 31, 2022
Accounting Policies [Abstract] |
Summary of amounts in income tax expense related to investments in qualifying affordable housing projects | The table below summarizes the amounts in income tax expense related to ASB’s LIHTC investments:
Years ended December 31 | 2022 |  | 2021 |  | 2020
(in millions) |  |  |  |  |
Amounts in income taxes related to low-income housing tax credit investments |  |  |  |  |
Amortization recognized in the provision for income taxes | $ | (12.0) |  |  | $ | (10.3) |  |  | $ | (9.6) |
Tax credits and other tax benefits recognized in the provision for income taxes | 16.3 |  |  | 13.9 |  |  | 13.7 |
Net benefit to income tax expense | $ | 4.3 |  |  | $ | 3.6 |  |  | $ | 4.1 |

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