Retirement Plans, Postretirement and Postemployment Benefits - Change in Projected Benefit Obligation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension
Defined Benefit Plan Disclosure [Line Items]
Net projected benefit obligation at beginning of year	$ 857.6	$ 1,135.5
Service cost	32.9	48.1	$ 46.2
Interest cost	51.3	41.2	35.7
Actuarial loss (gain)	72.6	(363.3)
Gross benefits paid	(45.2)	(52.0)
Plan amendments	0.0	48.1
Net projected benefit obligation at end of year	969.2	857.6	1,135.5
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net projected benefit obligation at beginning of year	8.9	11.4
Interest cost	0.5	0.4	0.3
Participants' contributions	0.7	0.6
Actuarial loss (gain)	(0.1)	(1.9)
Gross benefits paid	(1.7)	(1.6)
Net projected benefit obligation at end of year	$ 8.3	$ 8.9	$ 11.4