Employee Benefit Plans - Components of Net Periodic Cost for Defined Benefit Pension Plan and for Postretirement Benefit Plan (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic pension cost			$ 2.4	$ 4.4
Defined Benefit Pension Plan [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	$ 2.2	$ 1.7	4.4	3.4
Actuarial loss (gain) amortization	3.4	4.3	6.8	8.6
Less: Expected return on plan assets	(4.0)	(3.3)	(7.9)	(6.6)
Net periodic pension cost	1.6	2.7	3.3	5.4
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	0.1	0.1	0.1	0.1
Actuarial loss (gain) amortization	(0.5)	(0.5)	(1.0)	(1.0)
Prior service credit amortization		(0.1)		(0.1)
Net periodic pension cost	$ (0.4)	$ (0.5)	$ (0.9)	$ (1.0)