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
 6 Months Ended
Jun. 30, 2018
USD ($)
Dec. 31, 2017
USD ($)
Employees
Dec. 31, 2007
USD ($)
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  
Central States Pension Fund      
Defined Benefit Plan Disclosure [Line Items]      
Withdrawal liability     $ 6,100
Pension liability $ 4,000    
Multiemployer Plans, Pension [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Multi-employer Plans, Withdrawal Obligation, Fair Value Disclosure 841 $ 921  
Other noncurrent liabilities | Multiemployer Plans, Pension [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer Plans, Withdrawal Obligation, Present Value 856 859  
Other current liabilities | Multiemployer Plans, Pension [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer Plans, Withdrawal Obligation, Present Value $ 8 $ 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 48    
Defined Benefit Pension Plan | U.S. Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Amount contributed to company- sponsored benefit plans $ 50    
U.S. Postretirement Medical Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Amount contributed to company- sponsored benefit plans $ 42    
Estimated future employer contributions to defined benefit plan, current fiscal year 37