Defined Benefit Plans - Components of Net Periodic Benefit Cost for Pension and Postretirement Benefits (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 losses (gains)	$ 0.8	$ 3.2	$ 34.1
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	0.4
Interest cost	24.0	28.3
Recognition of actuarial losses (gains)	(32.4)	70.6
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.6	0.4
Interest cost	0.4	0.2
Recognition of actuarial losses (gains)	(0.7)	0.2
Net Periodic Benefit Cost | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	0.4	0.4
Interest cost	24.0	28.3	32.9
Expected return on plan assets	(34.9)	(32.8)	(35.2)
Recognition of actuarial losses (gains)	1.1	2.7	34.1
Settlement/Curtailment losses (gains)		0.6	0.1
Amortization of prior service credits
Net periodic benefit (income) cost	(9.4)	(0.8)	32.3
Net Periodic Benefit Cost | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.6	0.4	0.2
Interest cost	0.4	0.2	0.2
Recognition of actuarial losses (gains)	(0.3)	0.1	0.6
Settlement/Curtailment losses (gains)			(0.1)
Amortization of prior service credits			0.2
Net periodic benefit (income) cost	$ 0.7	$ 0.7	$ 1.1