Other Current and Non-Current Liabilities - Schedule of Other Non-Current Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Other Liabilities Noncurrent [Abstract]
Deferred consideration payable from acquisitions	$ 25.3	$ 24.4
Uncertain tax positions, including interest and penalties	25.0	24.8
Contingent consideration obligation		213.6
Accrued payables from acquisitions	25.0	136.0
Other non-current liabilities	3.0	2.3
Total other non-current liabilities	$ 78.3	$ 401.1