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Income Taxes - Roll-forward of Unrecognized Tax Benefits and Associated Accrued Interest and Penalties (Detail) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2024 | Dec. 31, 2023
Income Tax Contingency [Line Items] |  |
Opening balance at January 1 | $ 14.8 |
Increase for tax positions of prior periods | 0.8 |
Decrease for settlement of tax positions | (4.6) |
Closing balance at September 30 | 11.0 |
Current | 0.0 | $ (1.2)
Non-current | 11.0 | $ 13.6
Interest and Penalties [Member] |  |
Income Tax Contingency [Line Items] |  |
Opening balance at January 1 | 4.3 |
Increase for tax positions of prior periods | 0.8 |
Decrease for settlement of tax positions | (1.3) |
Closing balance at September 30 | 3.8 |
Current | 0.0 |
Non-current | 3.8 |
Unrecognized Tax Benefits [Member] |  |
Income Tax Contingency [Line Items] |  |
Opening balance at January 1 | 10.5 |
Increase for tax positions of prior periods | 0.0 |
Decrease for settlement of tax positions | (3.3) |
Closing balance at September 30 | 7.2 |
Current | 0.0 |
Non-current | $ 7.2 |

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