Retirement Plans, Postretirement and Postemployment Benefits - Net Periodic Benefit Cost Recognized in Comprehensive Earnings (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain)	$ 1.0	$ (1.7)	$ 1.2
Pension
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss (gain)	11.7	32.1	13.3
Net prior service cost (credit)	6.4
Prior service (cost) credit		(0.1)	(0.3)
Actuarial gain (loss)	(16.0)	(12.8)	(14.1)
Settlement (charge) credit		(2.9)
Total	2.1	16.3	(1.1)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net prior service cost (credit)			(3.9)
Prior service (cost) credit	0.8	2.1	1.7
Actuarial gain (loss)	0.5	0.2	0.4
Total	$ 2.3	$ 0.6	$ (0.6)