Significant Accounting Policies - Noncurrent Deferred Tax Assets Recorded in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Equity [Abstract]
Balance at beginning of period, Pension and Postretirement Benefit Plans	$ 80.2	$ 88.7	$ 69.7	$ 89.4
Tax effect of other comprehensive loss (earnings)	(0.7)	(0.8)	9.8	(1.5)
Balance at end of period, Pension and Postretirement Benefit Plans	$ 79.5	$ 87.9	$ 79.5	$ 87.9