Share-Based Compensation Expenses (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Share-Based Payment Arrangement [Abstract]
Option awards	$ 2.3	$ 1.9	$ 7.6	$ 7.7
Other share-based awards	7.9	10.6	12.9	16.8
Total share-based compensation before tax	10.2	12.5	20.5	24.5
Tax benefit	2.5	3.0	5.0	5.8
Total share-based compensation expense included in net income	$ 7.7	$ 9.5	$ 15.5	$ 18.7