LEASES - Components of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Lessee, Lease, Description [Line Items]
Short-term lease cost	$ 2	$ 2	$ 1
Variable lease cost	1,733	1,447	1,406
Amortization of finance lease liabilities	44	106	112
Interest on finance lease liabilities	5	15	19
Total net lease cost	2,059	1,842	1,823
Sublease income	7	17	41
Aircraft
Lessee, Lease, Description [Line Items]
Operating lease cost	186	188	204
Other
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 89	$ 84	$ 81