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Income Taxes - Roll-forward of Unrecognized Tax Benefits and Associated Accrued Interest and Penalties (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Income Tax Contingency [Line Items] |  |  |
Opening balance at January 1 | $ 14.8 | $ 13.4 | $ 16.3
Reductions for tax positions of prior periods | (15.6) | 0.0 | (3.1)
Additions for tax positions of prior periods | 0.8 | 1.4 | 0.2
Closing balance at December 31 | 0.0 | 14.8 | 13.4
Current | 0.0 | (1.2) | 0.0
Non-current | 0.0 | 13.6 | 13.4
Unrecognized Tax Benefits [Member] |  |  |
Income Tax Contingency [Line Items] |  |  |
Opening balance at January 1 | 10.5 | 10.2 | 13.2
Reductions for tax positions of prior periods | (10.5) | 0.0 | (3.1)
Additions for tax positions of prior periods | 0.0 | 0.3 | 0.1
Closing balance at December 31 | 0.0 | 10.5 | 10.2
Current | 0.0 | (1.0) | 0.0
Non-current | 0.0 | 9.5 | 10.2
Interest and Penalties [Member] |  |  |
Income Tax Contingency [Line Items] |  |  |
Opening balance at January 1 | 4.3 | 3.2 | 3.1
Reductions for tax positions of prior periods | (5.1) | 0.0 | 0.0
Additions for tax positions of prior periods | 0.8 | 1.1 | 0.1
Closing balance at December 31 | 0.0 | 4.3 | 3.2
Current | 0.0 | (0.2) | 0.0
Non-current | $ 0.0 | $ 4.1 | $ 3.2

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