Retirement Plans, Postretirement and Postemployment Benefits - Net Periodic Benefit Credit or Cost Not Yet Recognized (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Pension
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) - Gross	$ 42.4	$ 48.2
Actuarial (gain) loss - Gross	63.4	43.2
Total - Gross	105.8	91.4
Prior service cost (credit) - Net of tax	20.0	20.3
Actuarial (gain) loss - Net of tax	29.9	18.2
Total - Net of tax	49.9	38.5
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) - Gross	(0.4)	(0.7)
Actuarial (gain) loss - Gross	(3.7)	(4.1)
Total - Gross	(4.1)	(4.8)
Prior service cost (credit) - Net of tax	(0.2)	(0.3)
Actuarial (gain) loss - Net of tax	(1.7)	(1.7)
Total - Net of tax	$ (1.9)	$ (2.0)