Retirement Plans - Amounts Recognized in Other Comprehensive Income (Loss) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of Net actuarial loss (gain)	$ 10.0
Amortization of Net prior service credit	0.1
Amounts arising during the period, Net actuarial loss	5.3
Amounts arising during the period, Net prior service cost	(0.1)
Amounts arising during the period, Settlements	1.4
Amounts arising during the period, Foreign currency (gain) loss	(0.6)
Total	16.1
OPEB
Defined Benefit Plan Disclosure [Line Items]
Amortization of Net actuarial loss (gain)	(0.7)
Amortization of Net prior service credit	(5.4)
Amounts arising during the period, Net actuarial loss	0.3
Amounts arising during the period, Net prior service cost	0.0
Amounts arising during the period, Settlements	0.0
Amounts arising during the period, Foreign currency (gain) loss	0.0
Total	$ (5.8)