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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, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Income Tax Contingency [Line Items] |  |  |
Opening balance at January 1 | $ 13.4 | $ 16.3 | $ 16.0
Reductions for tax positions of prior periods | 0.0 | (3.1) | (1.3)
Additions for tax positions of prior periods | 1.4 | 0.2 | 1.6
Closing balance at December 31 | 14.8 | 13.4 | 16.3
Current | (1.2) | 0.0 | 0.0
Liability for Uncertainty in Income Taxes, Noncurrent | 13.6 | 13.4 | 16.3
Interest and Penalties [Member] |  |  |
Income Tax Contingency [Line Items] |  |  |
Opening balance at January 1 | 3.2 | 3.1 | 2.4
Reductions for tax positions of prior periods | 0.0 | 0.0 | 0.0
Additions for tax positions of prior periods | 1.1 | 0.1 | 0.7
Closing balance at December 31 | 4.3 | 3.2 | 3.1
Current | (0.2) | 0.0 | 0.0
Liability for Uncertainty in Income Taxes, Noncurrent | 4.1 | 3.2 | 3.1
Unrecognized Tax Benefits [Member] |  |  |
Income Tax Contingency [Line Items] |  |  |
Opening balance at January 1 | 10.2 | 13.2 | 13.6
Reductions for tax positions of prior periods | 0.0 | (3.1) | (1.3)
Additions for tax positions of prior periods | 0.3 | 0.1 | 0.9
Closing balance at December 31 | 10.5 | 10.2 | 13.2
Current | (1.0) | 0.0 | 0.0
Liability for Uncertainty in Income Taxes, Noncurrent | $ 9.5 | $ 10.2 | $ 13.2

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