Employee Benefits - Components of Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Curtailment gain	$ (0.3)
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.4	$ 0.4
Interest cost	3.7	4.1
Expected return on assets	(3.8)	(4.1)
Settlement expense	1.7
Curtailment gain	(0.2)
Recognized actuarial (gain) loss	1.0	1.1
Net periodic benefit cost (credit)	2.8	1.5
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.1
Interest cost	0.4	0.5
Curtailment gain	(0.1)
Recognized actuarial (gain) loss	(1.8)	(2.1)
Net periodic benefit cost (credit)	$ (1.4)	$ (1.6)