Commitments and Contingencies (Asbestos Liability) (Detail)	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) Claim	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2018 USD ($) Claim	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2018	Oct. 06, 2016 USD ($)	Sep. 30, 2016 USD ($)	Apr. 22, 2016 USD ($)	Feb. 09, 2016 USD ($)	Jul. 02, 2015 USD ($)	Jun. 16, 2014 USD ($)	Sep. 17, 2013 USD ($)	Jul. 31, 2013 USD ($)	Mar. 01, 2013 USD ($)	Feb. 25, 2013 USD ($)	Oct. 23, 2012 USD ($)	Aug. 17, 2011 USD ($)	Feb. 23, 2011 USD ($)	Mar. 23, 2010 USD ($)
Loss Contingencies [Line Items]
Payments for asbestos-related fees and costs, net of insurance recoveries					$ 34,900,000	$ 28,200,000
Current portion of total estimated liability	$ 85,000,000				$ 85,000,000		$ 85,000,000
Airplane Operating Lease Period Years					7
Fair Value Of Residual Value Guarantee	11,100,000				$ 11,100,000
Fair Value Of Residual Value Guarantee, Fair Value of Operating Lease Asset Threshold	$ 14,400,000				$ 14,400,000
Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Pending claims	29,920	31,980	35,560	36,052	29,920	31,980	32,234	36,052		30,990
Payments for asbestos-related fees and costs, net of insurance recoveries	$ 32,000,000	$ 13,500,000			$ 34,900,000	$ 28,200,000	$ 62,500,000
Cumulative claims resolved | Claim	134,000				134,000
Settlement cost	$ 580,000,000				$ 580,000,000
Average settlement cost per resolved claim							7,800	$ 3,900	$ 3,100
Cumulative average settlement cost per resolved claim	4,300				4,300
Estimated payments to current and future claimants	36,000,000,000				36,000,000,000
Additional liability				$ 227,000,000
Liability for claims	559,000,000			$ 696,000,000	559,000,000			$ 696,000,000
Percentage Of Asbestos Liability Attributable To Settlement And Denfese Costs For Future Claims				80.00%				80.00%
Current portion of total estimated liability	$ 85,000,000				$ 85,000,000
Number of coverage in place agreements with excess insurer groups	11				11
Number of buyout agreements with excess insurer groups	10				10
Aggregate value of policy buyout agreements	$ 82,500,000				$ 82,500,000
Forecasted percentage of liability that would be reimbursed by insurers				21.00%				21.00%
Insurance reimbursement asset	104,000,000			$ 143,000,000	104,000,000			$ 143,000,000
Gross Settlement And Defense Incurred Costs	$ 41,100,000	16,800,000			$ 55,900,000	44,800,000	$ 88,300,000
Mesothelioma Claims Percentage Pending Asbestos Claims				10.00%				10.00%
Mesothelioma Claims Percentage Aggregate Settlement Defense Costs				90.00%				90.00%
Frank Paasch | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Jury Verdict																				$ 2,500,000
PaidJuryVerdict		300,000
Share Of Responsibility Of Verdict																				10.00%
James Nelson | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Jury Verdict																								$ 14,500,000
Share Of Responsibility Of Verdict																								9.09%
Court judgment against all parties held responsible																							$ 4,000,000
Additional interest on the compensation awarded																							$ 10,000
Larry Bell | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Share Of Responsibility Of Verdict																								5.00%
Ronald Dummitt | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court written decision																						$ 8,000,000
Court Judgment																						4,900,000
courtjudgmentwithinterest												$ 6,600,000
Jury Verdict																						$ 32,000,000
Jury verdict percentage of responsibility.																						99.00%
Frank Vincinguerra | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Jury Verdict																				$ 2,300,000
PaidJuryVerdict				$ 600,000
Share Of Responsibility Of Verdict																				20.00%
Gerald Suttner | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment																					$ 100,000
courtjudgmentwithinterest				$ 200,000				$ 200,000
Share Of Responsibility Of Verdict																					4.00%
Plaintiff's Damages																					$ 3,000,000
Ivo Peraica | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment																			$ 10,600,000
Reduced Damages											$ 4,250,000
CourtJudgmentIncludingSetoffs											1,940,000
Paid Judgment Pursuant to Appeal			$ 2,700,000
Jury Verdict Total																			35,000,000
Court_Reduced_Verdict																			$ 18,000,000
Holdsworth [Member] | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment																		$ 1,700,000
Motion to enter judgment																		1,000,000
Jury Verdict Total																		$ 3,100,000
Richard DeLisle [Member] | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment																	$ 1,300,000
Jury Verdict																	$ 8,000,000
Share Of Responsibility Of Verdict																	16.00%
Ivan Sweberg [Member] | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment																$ 5,300,000
Reduced Damages											9,500,000
CourtJudgmentIncludingSetoffs											4,730,000
Paid Judgment Pursuant to Appeal			$ 5,700,000
Jury Verdict Total																15,000,000
Court_Reduced_Verdict																10,000,000
Selwyn Hackshaw [Member] | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment																3,100,000
Reduced Damages											3,000,000
CourtJudgmentIncludingSetoffs											$ 0
Jury Verdict Total																10,000,000
Court_Reduced_Verdict																$ 6,000,000
James Poage [Member] | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Compensatory Damages															$ 1,500,000
Additional Damages															10,000,000
Court Judgment															$ 10,800,000
Valent Rabovsky [Member] | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment													$ 400,000
Jury Verdict Total														$ 1,085,000
Share Of Responsibility Of Verdict														30.00%
George Coulbourn [Member] | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Court Judgment													6,800,000
Jury Verdict Total													9,000,000
Court Reduced damages													$ 5,000,000
Share Of Responsibility Of Verdict													20.00%
Geoffrey_Anisansel [Member] | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Jury Verdict Total		$ 20,000,000				$ 20,000,000
New York | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Pending claims | Claim	18,000				18,000
Mississippi | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Pending claims | Claim	400				400
Texas | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Pending claims | Claim	400				400
Ohio | Asbestos Commitments and Contingencies
Loss Contingencies [Line Items]
Pending claims | Claim	200				200