LONG-TERM DEBT - SCHEDULE OF LONG-TERM DEBT (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended
	Jul. 31, 2024	Jun. 30, 2024	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Debt Instrument [Line Items]
Debt Issuance Costs, Net		$ (14)	$ (14)		$ (15)
Total		2,672	2,672		2,471
Less current portion		(359)	(359)		(289)
Long-term debt, less current portion		$ 2,313	$ 2,313		$ 2,182
Weighted-average fixed-interest rate		3.30%	3.30%		3.40%
Weighted-average variable-interest rate		6.90%	6.90%		6.80%
Long-term debt payments			$ 149	$ 149
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 39.06	$ 39.06
Proceeds from issuance of debt			$ 279	$ 0
Proceeds from Issuance of Long-term Debt			$ 348
Debt, Weighted Average Interest Rate		4.70%	4.70%
Proceeds from Issuance of Long-term Debt			$ 348
Line of Credit Facility, Maximum Borrowing Capacity		$ 626	626
Scheduled Debt Payments [Member]
Debt Instrument [Line Items]
Long-term debt payments			149
Fixed rate notes payable due through 2029 [Member]
Debt Instrument [Line Items]
Total		68	68		$ 80
US Treasury CARES Act Loan [Member]
Debt Instrument [Line Items]
Adjustments to Additional Paid in Capital, Warrant Issued			30
July 2020 EETC
Debt Instrument [Line Items]
Total		779	779		835
Credit Facility 1 [Member] | Secured by certain accounts receivable, spare engines, spare parts and ground service equipment [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		150	150
PSP Notes Payable through 2031
Debt Instrument [Line Items]
Total		600	600		600
Variable rate notes payable due through 2035
Debt Instrument [Line Items]
Total		1,239	1,239		$ 971
Proceeds from Issuance of Long-Term Debt, Cash proceeds [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Long-term Debt		280
Proceeds from Issuance of Long-term Debt		280
Proceeds from Issuance of Long-Term Debt, Cash proceeds [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Long-term Debt	$ 67
Proceeds from Issuance of Long-term Debt	$ 67
Proceeds from Issuance of Long-Term Debt, Noncash proceeds [Member]
Debt Instrument [Line Items]
Proceeds from Issuance of Long-term Debt			68
Proceeds from Issuance of Long-term Debt			68
Variable Rate debt with interest rate swap [Member] | Interest rate swaps agreements [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount		223	223
Derivative, Notional Amount		$ 223	$ 223