Commitments and Contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Environmental Remediation Obligations [Abstract]
Balance at the beginning of the year	$ 103.4
Payments, net	(3.4)
Balance at the end of the period	100.0
Amounts recognized in our Condensed Consolidated Balance Sheet at the end of the period:
Current liabilities		$ 4.5	$ 6.5
Noncurrent liabilities		95.5	96.9
Total	$ 103.4	$ 100.0	$ 103.4