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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
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