Income Taxes - Roll-forward of Unrecognized Tax Benefits and Associated Accrued Interest and Penalties (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Income Tax Contingency [Line Items]
Opening balance at January 1	$ 13.4
Net change for tax positions of prior periods	0.7
Closing balance at September 30	14.1
Current	0.0
Non-current	14.1	$ 13.4
Interest and Penalties [Member]
Income Tax Contingency [Line Items]
Opening balance at January 1	3.2
Net change for tax positions of prior periods	0.7
Closing balance at September 30	3.9
Current	0.0
Non-current	3.9
Unrecognized Tax Benefits [Member]
Income Tax Contingency [Line Items]
Opening balance at January 1	10.2
Net change for tax positions of prior periods	0.0
Closing balance at September 30	10.2
Current	0.0
Non-current	$ 10.2