Quarterly report pursuant to Section 13 or 15(d)

EMPLOYEE BENEFIT PLANS - Additional Information (Details)

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EMPLOYEE BENEFIT PLANS - Additional Information (Details)
$ in Millions
 1 Months Ended 3 Months Ended
Jan. 31, 2023
USD ($)
Mar. 31, 2024
USD ($)
employee
Dec. 31, 2023
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer plans, payment term   39 years  
Central States Pension Fund      
Defined Benefit Plan Disclosure [Line Items]      
Government assistance, amount $ 35,800    
National Master Agreement and Various Supplemental Agreements      
Defined Benefit Plan Disclosure [Line Items]      
Number of employees covered | employee   310,000  
Teamsters      
Defined Benefit Plan Disclosure [Line Items]      
Number of employees covered | employee   10,000  
Independent Pilots Association      
Defined Benefit Plan Disclosure [Line Items]      
Number of employees covered | employee   3,300  
Teamsters Local 2727      
Defined Benefit Plan Disclosure [Line Items]      
Number of employees covered | employee   1,900  
International Association Of Machinists And Aerospace Workers      
Defined Benefit Plan Disclosure [Line Items]      
Number of employees covered | employee   3,000  
Defined Benefit Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Multi-employer plans, withdrawal obligation, fair value   $ 685 $ 710
Defined Benefit Pension Plan | Long term debt      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer plans, withdrawal obligation, present value   811 813
Defined Benefit Pension Plan | Other current liabilities      
Defined Benefit Plan Disclosure [Line Items]      
Multiemployer plans, withdrawal obligation, present value   9 $ 9
Defined Benefit Pension Plan | U.S. Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Amount contributed to company- sponsored benefit plans   19  
U.S. Postretirement Medical Benefits | U.S. Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Amount contributed to company- sponsored benefit plans   31  
Estimated future employer contributions to defined benefit plan, current fiscal year   $ 87