REVENUE - Air Traffic Liability - Loyalty Program Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Air traffic liability
Beginning balance	$ 5,189	$ 4,789
Amounts deferred associated with points awarded	3,466	3,506
Ending balance	4,916	5,189
Passenger Customer
Air traffic liability
Revenue recognized from points redeemed	(3,639)	(3,028)
Other
Air traffic liability
Revenue recognized from points redeemed	$ (100)	$ (78)