Commitments and Contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Environmental Remediation Obligations [Abstract]
Balance at the beginning of the year	$ 99.7	$ 103.4	$ 117.5
Additions charged to expense, net	0.7	0.3	3.1
Payments, net	(1.9)	(4.0)	(17.2)
Changes in currency exchange rates and other	0.1
Balance at the end of the year	98.6	99.7	103.4
Amounts recognized in our Consolidated Balance Sheet at the end of the year:
Current liabilities				$ 3.4	$ 4.5	$ 6.5
Noncurrent liabilities				95.2	95.2	96.9
Total	$ 98.6	$ 99.7	$ 103.4	$ 98.6	$ 99.7	$ 103.4