Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Amounts Recognized on Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Noncurrent asset pension and postretirement benefits	$ 42.0
Current pension and postretirement benefits	(7.2)	$ (6.4)
Noncurrent pension, postretirement and postemployment benefits	(108.8)	(103.4)
Net amount recognized at end of year	(74.0)	(109.8)
Current pension and postretirement benefits	(1.3)	(2.0)
Noncurrent pension, postretirement and postemployment benefits	(11.3)	(11.0)
Net amount recognized at end of year	$ (12.6)	$ (13.0)