Share-Based Compensation (Costs Associated with Share-Based Compensation Plans) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 9.7	$ 8.9	$ 42.5	$ 40.9
RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	7.0	6.5	32.8	32.3
PRSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	1.1	1.0	4.6	3.5
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 1.6	$ 1.4	$ 5.1	$ 5.1