COMMITMENTS AND CONTINGENCIES - Narrative (Details) $ in Millions		3 Months Ended	12 Months Ended
	Dec. 31, 2024 USD ($)	Dec. 31, 2024 USD ($) aircraft	Dec. 31, 2024 USD ($) aircraft	Dec. 31, 2023 USD ($)	Apr. 30, 2023 gate	Mar. 31, 2022 gate
Payment Guarantee
Other Commitments [Line Items]
Principal amount of guarantee | $	$ 49	$ 49	$ 49
Net present value of future principal and interest payments | $	52	52	52	$ 65
Los Angeles World Airports
Other Commitments [Line Items]
New airport gates | gate					9
Projected airport improvement costs | $	2,300	2,300	2,300
Payments for airport projects | $	88
William P. Hobby Airport
Other Commitments [Line Items]
New airport gates | gate						7
Projected airport improvement costs | $	$ 470	$ 470	$ 470
737 MAX 8
Other Commitments [Line Items]
Number of aircraft deliveries | aircraft			22
B-737-700
Other Commitments [Line Items]
Number of aircraft retirements | aircraft			34
B-737-800
Other Commitments [Line Items]
Number of aircraft retirements | aircraft			2
737 MAX 7 | Year 2025
Other Commitments [Line Items]
Number of aircraft orders exercised | aircraft		8
737 MAX 7 | Year 2026
Other Commitments [Line Items]
Number of aircraft orders exercised | aircraft		5