Retirement Plans, Postretirement and Postemployment Benefits - Schedule of Funded Status (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Pension
Defined Benefit Plan Disclosure [Line Items]
Funded status of the plan at end of year	$ (74.0)	$ (109.8)
Accrued benefit cost	(74.0)	(109.8)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Funded status of the plan at end of year	(12.6)	(13.0)
Accrued benefit cost	$ (12.6)	$ (13.0)