Retirement Plans - Amounts Recognized in Other Comprehensive Loss (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of Net actuarial loss (gain)	$ 6.1
Amortization of Net prior service credit	0.0
Amounts arising during the period, Net actuarial (gain) loss	(39.5)
Amounts arising during the period, Net prior service cost	(2.2)
Amounts arising during the period, Settlements	(0.1)
Amounts arising during the period, Foreign currency gain	(0.4)
Total	(36.1)
OPEB
Defined Benefit Plan Disclosure [Line Items]
Amortization of Net actuarial loss (gain)	(1.7)
Amortization of Net prior service credit	(5.4)
Amounts arising during the period, Net actuarial (gain) loss	3.4
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	0.0
Total	$ (3.7)