LEASES - Related Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Assets
Accumulated amortization	$ 452	$ 477
Operating	1,369	1,223
Finance	102	125
Total lease assets	$ 1,471	$ 1,348
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Flight equipment	Flight equipment
Current
Operating	$ 328	$ 208
Finance	$ 22	$ 29
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Less current maturities	Less current maturities
Noncurrent
Operating	$ 1,031	$ 985
Finance	$ 69	$ 75
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term debt less current maturities	Long-term debt less current maturities
Total lease liabilities	$ 1,450	$ 1,297