v3.24.2
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, 2024
Jun. 30, 2023
Jun. 30, 2024
Jun. 30, 2023
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]        
Net periodic pension cost     $ 5.1 $ 0.7
Defined Benefit Pension Plan [Member]        
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]        
Interest cost $ 4.1 $ 4.3 8.2 8.6
Actuarial loss (gain) amortization 3.3 2.1 6.6 4.2
Less: Expected return on plan assets (4.4) (5.6) (8.8) (11.1)
Net periodic pension cost 3.0 0.8 6.0 1.7
Other Postretirement Benefits Plan [Member]        
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]        
Interest cost 0.1 0.1 0.2 0.2
Actuarial loss (gain) amortization (0.6) (0.6) (1.1) (1.2)
Net periodic pension cost $ (0.5) $ (0.5) $ (0.9) $ (1.0)