Employee Benefit Plans - Schedule of Other Comprehensive (Income) Loss Related to Pension Benefit Plans (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	[1]	$ (21.2)	$ (9.8)	$ 7.6
Tax expense		(5.7)	(2.4)	(0.0)
Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss		(8.0)	1.0	21.4
Amortization of net actuarial gain (loss)		(15.7)	(12.7)	(14.2)
Tax expense		6.4	2.9
Other comprehensive loss (income), net of tax		(17.3)	(8.8)	7.2
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss			(0.7)	(2.1)
Amortization of net actuarial gain (loss)		2.5	2.6	2.5
Tax expense		(0.7)	(0.5)
Other comprehensive loss (income), net of tax		$ 1.8	$ 1.4	$ 0.4

[1] The amount of the pension liability adjustment recognized in the Consolidated Statements of Operations within other expense (income), net was $13.2 million, $10.1 million, and $11.7 million during the years ended December 31, 2020, 2019, and 2018, respectively.