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
 9 Months Ended 12 Months Ended
Dec. 31, 2007
USD ($)
Sep. 30, 2019
USD ($)
Dec. 31, 2018
USD ($)
Employees
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer Plans, Payment Term   43 years  
Number of employees under a national master agreement and various supplemental agreements with local unions affiliated with Teamsters | Employees     283,000
Number of pilots under a collective bargaining agreement with the Independent Pilots Association | Employees     2,800
Ground mechanics employed under Teamster Local 272 | Employees     1,400
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   $ 941 $ 832
Multiemployer Plans, Pension [Member] | Central States Pension Fund      
Defined Benefit Plan Disclosure [Line Items]      
Payment of withdrawal liability $ 6,100    
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)     1,600
Pension liability   4,000  
Long term debt | Multiemployer Plans, Pension [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer Plans, Withdrawal Obligation, Present Value   847 852
Other current liabilities | Multiemployer Plans, Pension [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer Plans, Withdrawal Obligation, Present Value   7 $ 7
Defined Benefit Pension Plan | U.S. Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Amount contributed to company- sponsored benefit plans   2,065  
Estimated future employer contributions to defined benefit plan, current fiscal year   22,000  
U.S. Postretirement Medical Benefits | U.S. Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Amount contributed to company- sponsored benefit plans   256  
Pro Forma | Maximum [Member] | Multiemployer Plans, Pension [Member] | Central States Pension Fund      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)   $ 2,400