Commitments and Contingencies (Other Contingencies) (Detail) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2012 a	Jul. 31, 2006
Loss Contingencies [Line Items]
Airplane operating lease period, years				7
Fair Value Of Residual Value Guarantee	$ 11.1			$ 11.1
Fair Value Of Residual Value Guarantee, Fair Value of Operating Lease Asset Threshold	14.4			14.4
Payments for airplane				6.7
Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Gross Settlement And Defense Incurred Costs	41.1	$ 16.8		55.9	$ 44.8	$ 88.3
Environmental Claims For A Site In Goodyear Arizona
Loss Contingencies [Line Items]
Estimated liability	36.2			36.2
Amount of additional remediation activities			$ 49.0
Accrued environmental loss contingencies current	9.4			9.4
Loss contingency reimbursement rate								21.00%
Other receivables	$ 7.7			$ 7.7
Environmental Claims For Crab Orchard National Wildlife Refuge Superfund Site
Loss Contingencies [Line Items]
Approximate size of referenced site, acres | a							55,000