Quarterly report pursuant to Section 13 or 15(d)

EMPLOYEE BENEFIT PLANS - Additional Information (Detail)

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EMPLOYEE BENEFIT PLANS - Additional Information (Detail)
$ in Millions
 3 Months Ended 9 Months Ended
Dec. 31, 2007
USD ($)
Jun. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
Dec. 31, 2017
USD ($)
Employees
Defined Benefit Plan Disclosure [Line Items]        
Defined benefit plan, net actuarial gain   $ 569    
Defined benefit plan, curtailments   1,525    
Defined benefit plan, net actuarial loss   $ 956    
Defined benefit plan, assumptions used calculating benefit obligation, discount rate   0.32%    
Defined benefit plan,actual return on plan assets   2.75%    
Actuarial gain loss corridor threshold   10.00%    
Multiemployer Plans, Payment Term     44 years  
Number of employees under a national master agreement and various supplemental agreements with local unions affiliated with Teamsters | Employees       280,000
Number of pilots under a collective bargaining agreement with the Independent Pilots Association | Employees       2,700
Majority of ground mechanics not employed under agreements | Employees       3,100
Multiemployer Plans, Pension [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Multi-employer Plans, Withdrawal Obligation, Fair Value Disclosure     $ 836 $ 921
Multiemployer Plans, Pension [Member] | Central States Pension Fund        
Defined Benefit Plan Disclosure [Line Items]        
Payment of withdrawal liability $ 6,100      
Pension liability     4,000  
Other noncurrent liabilities | Multiemployer Plans, Pension [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Multiemployer Plans, Withdrawal Obligation, Present Value     854 859
Other current liabilities | Multiemployer Plans, Pension [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Multiemployer Plans, Withdrawal Obligation, Present Value     $ 7 $ 8
Minimum [Member] | Non-union employees        
Defined Benefit Plan Disclosure [Line Items]        
Employer contribution percentage     5.00%  
Maximum [Member] | Non-union employees        
Defined Benefit Plan Disclosure [Line Items]        
Employer contribution percentage     8.00%  
Defined Benefit Pension Plan        
Defined Benefit Plan Disclosure [Line Items]        
Estimated future employer contributions to defined benefit plan, current fiscal year     $ 24  
Defined Benefit Pension Plan | U.S. Pension Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Amount contributed to company- sponsored benefit plans     74  
U.S. Postretirement Medical Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Amount contributed to company- sponsored benefit plans     63  
Estimated future employer contributions to defined benefit plan, current fiscal year     $ 16