Retirement Plans, Postretirement and Postemployment Benefits - Net Periodic Benefit Cost Recognized in Comprehensive Earnings (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain)	$ 0.5	$ 1.0	$ (1.7)
Pension
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain)	34.7	11.7	32.1
Net prior service cost (credit)		6.4
Prior service (cost) credit	(0.7)		(0.1)
Actuarial gain (loss)	(14.5)	(16.0)	(12.8)
Settlement (charge) credit	(3.7)		(2.9)
Total	15.8	2.1	16.3
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	0.8	0.8	2.1
Actuarial gain (loss)	0.2	0.5	0.2
Total	$ 1.5	$ 2.3	$ 0.6