Retirement Plans, Postretirement and Postemployment Benefits - Net Periodic Benefit Credit or Cost Not Yet Recognized (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit) - Gross	$ 6.4
Actuarial (gain) loss - Gross	229.4	$ 233.7
Total - Gross	235.8	233.7
Prior service cost (credit) - Net of tax	4.0
Actuarial (gain) loss - Net of tax	144.5	146.6
Total - Net of tax	148.5	146.6
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit) - Gross	(3.0)	(3.8)
Actuarial (gain) loss - Gross	(2.7)	(4.2)
Total - Gross	(5.7)	(8.0)
Prior service cost (credit) - Net of tax	(1.9)	(2.4)
Actuarial (gain) loss - Net of tax	(1.7)	(2.7)
Total - Net of tax	$ (3.6)	$ (5.1)