Defined Benefit Plans - Amounts in Accumulated Other Comprehensive loss that have not yet been Recognized as Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Recognition of actuarial loss	$ (0.8)	$ (3.2)	$ (34.1)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Recognition of actuarial loss	32.4	(70.6)
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Recognition of actuarial loss	0.7	(0.2)
Other Accumulated Other Comprehensive Income | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance	86.5	87.7
Recognition of actuarial loss	(1.1)	(2.7)
Current year actuarial (gain) loss	(45.8)	2.1
Net actuarial loss due to curtailment		(0.6)
Ending Balance	39.6	86.5	87.7
Other Accumulated Other Comprehensive Income | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance	0.6	(0.3)
Recognition of actuarial loss	0.3	(0.1)
Current year actuarial (gain) loss	(0.9)	1.0
Ending Balance	$ 0.0	$ 0.6	$ (0.3)