Share-Based Compensation Expenses (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-Based Payment Arrangement [Abstract]
Option awards	$ 2.0	$ 2.5	$ 9.7	$ 9.7
Other share-based awards	7.9	12.8	24.7	28.6
Total share-based compensation before tax	9.9	15.3	34.4	38.3
Tax benefit	2.4	3.7	8.2	9.2
Total share-based compensation expense included in net income	$ 7.5	$ 11.6	$ 26.2	$ 29.1