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 12 Months Ended
Dec. 31, 2007
USD ($)
Mar. 31, 2020
USD ($)
Dec. 31, 2019
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     290,000
Number of pilots under a collective bargaining agreement with the Independent Pilots Association | Employees     2,900
Ground mechanics employed under Teamster Local 272 | Employees     1,500
Majority of ground mechanics not employed under agreements | Employees     3,300
Multiemployer Plans, Pension [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Multi-employer Plans, Withdrawal Obligation, Fair Value Disclosure   $ 907 $ 929
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)     2,600
Pension liability   4,800  
Long term debt | Multiemployer Plans, Pension [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer Plans, Withdrawal Obligation, Present Value   843 845
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   19  
Estimated future employer contributions to defined benefit plan, current fiscal year   1,100  
U.S. Postretirement Medical Benefits | U.S. Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Amount contributed to company- sponsored benefit plans   203  
Pro Forma | Maximum | Multiemployer Plans, Pension [Member] | Central States Pension Fund      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)   $ 2,200