Postretirement Benefit Plans - Summary of Funded Status of Postretirement Benefit Plans and Presentation of Such Balances within Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0.5	$ 0.5	$ 321.8
Projected benefit obligation	214.3	242.8	525.4
Funded status	(213.8)	(242.3)
Amounts reported within:
Non-current assets	0.2	0.2
Accrued liabilities	(14.1)	(15.0)
Non-current liabilities	(199.9)	(227.5)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	0.5
Projected benefit obligation	107.9	124.5
Funded status	(107.4)	(124.0)
Amounts reported within:
Non-current assets	0.2	0.2
Accrued liabilities	(5.5)	(5.8)
Non-current liabilities	(102.1)	(118.4)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0	1.3
Projected benefit obligation	106.4	118.3	$ 116.6
Funded status	(106.4)	(118.3)
Amounts reported within:
Non-current assets	0.0	0.0
Accrued liabilities	(8.6)	(9.2)
Non-current liabilities	$ (97.8)	$ (109.1)