DEBT - Debt Obligations (Details) - USD ($) $ in Millions	Feb. 12, 2026	Dec. 31, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Less debt issuance costs and other		$ (45)	$ (46)
Total debt		5,309	4,933
Less current portion		540	442
Long-term debt, less current portion		$ 4,769	$ 4,491
Weighted-average fixed-interest rate		3.90%	3.90%
Weighted-average variable-interest rate		5.20%	6.30%
Fixed-rate notes payable due through 2037
Debt Instrument [Line Items]
Total debt, gross		$ 115	$ 56
Fixed-rate PSP notes payable due through 2031
Debt Instrument [Line Items]
Total debt, gross		630	688
Fixed-rate EETCs payable due through 2027
Debt Instrument [Line Items]
Total debt, gross		715	864
Fixed-rate Japanese Yen denominated notes payable due through 2031
Debt Instrument [Line Items]
Total debt, gross		51	88
Variable-rate Japanese Yen denominated notes payable through 2033
Debt Instrument [Line Items]
Total debt, gross		149	0
Variable-rate PSP notes payable due through 2030
Debt Instrument [Line Items]
Total debt, gross		62	0
Variable-rate notes payable due through 2037
Debt Instrument [Line Items]
Total debt, gross		1,639	1,283
Loyalty financing, variable-rate term loan facility due through 2031
Debt Instrument [Line Items]
Total debt, gross		743	750
Loyalty financing, fixed-rate notes due through 2031
Debt Instrument [Line Items]
Total debt, gross		$ 1,250	$ 1,250
Fixed Rate-Notes Payable, Due Through 2038 | Subsequent Event
Debt Instrument [Line Items]
Total debt, gross	$ 111