Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Components of Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 39.2	$ 30.8	$ 31.7
Interest cost	37.1	37.6	33.2
Expected return on assets	(58.4)	(47.9)	(46.0)
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 net periodic benefit cost (credit)	36.8	36.5	34.7
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.1	0.1
Interest cost	0.4	0.6	0.5
Prior service cost (credit)	(0.8)	(0.8)	(2.1)
Actuarial (gain) loss	(0.2)	(0.5)	(0.2)
Total net periodic benefit cost (credit)	$ (0.6)	$ (0.6)	$ (1.7)