Income Taxes - Roll-forward of Unrecognized Tax Benefits and Associated Accrued Interest and Penalties (Detail) - USD ($) $ in Millions	12 Months Ended
	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