Retirement Plans, Postretirement and Postemployment Benefits - Change in Projected Benefit Obligation (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	$ (1.6)
Pension
Defined Benefit Plan Disclosure [Line Items]
Net projected benefit obligation at beginning of year	847.9	879.3
Service cost	30.8	31.7	$ 26.9
Interest cost	37.6	33.2	36.1
Actuarial loss (gain)	95.2	(54.6)
Plan amendments	6.4
Gross benefits paid	(40.1)	(41.7)
Net projected benefit obligation at end of year	977.8	847.9	879.3
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net projected benefit obligation at beginning of year	13.3	15.3
Service cost	0.1	0.1	0.1
Interest cost	0.6	0.5	0.7
Participants' contributions	1.2	0.3
Gross benefits paid	(3.2)	(1.3)
Net projected benefit obligation at end of year	$ 13.0	$ 13.3	$ 15.3