Commitments and Contingencies - Changes in Accrued Environmental Remediation and Related Costs (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Environmental Remediation Obligations [Abstract]
Balance at the beginning of the year	$ 103.4
Additions charged (credited) to expense, net	(0.7)
Payments, net	(1.2)
Other, net	0.6
Balance at the end of period	102.1
Amounts recognized in our Condensed Consolidated Balance Sheet at the end of the period:
Current liabilities		$ 6.2	$ 6.5
Noncurrent liabilities		95.9	96.9
Total	$ 103.4	$ 102.1	$ 103.4