SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment, net (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Less: accumulated depreciation and amortization	$ (21,707)	$ (20,370)
Total property and equipment, net	35,486	33,109
Flight equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 40,976	38,091
Flight equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	25 years
Flight equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	34 years
Ground property and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 9,986	8,996
Ground property and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Ground property and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years
Information technology-related assets
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3,307	3,375
Information technology-related assets | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Information technology-related assets | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Flight and ground equipment under finance leases
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,862	1,950
Less: accumulated depreciation and amortization	(525)	(463)
Advance payments for equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,062	$ 1,067