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, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Recognition of actuarial loss	$ 1.2	$ (0.8)	$ (3.2)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Recognition of actuarial loss	155.9	26.2
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Recognition of actuarial loss	1.2	1.0
Other Accumulated Other Comprehensive Income | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance	32.4	70.1
Recognition of actuarial loss	0.3	(1.1)
Current year actuarial (gain) loss	17.0	(36.6)
Ending Balance	49.7	32.4	$ 70.1
Other Accumulated Other Comprehensive Income | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance	(0.4)
Recognition of actuarial loss	1.0	0.5
Current year actuarial (gain) loss	(1.1)	(0.9)
Ending Balance	$ (0.5)	$ (0.4)