SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2024 USD ($) segment	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) aircraft
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reimbursement costs	$ 390		$ 55
Accrued expense on settlement		$ 107
Impairment charges						$ 28
Number of aircraft under accelerated retirement | aircraft						10
Impaired of assets to be retired				$ 0	$ 0
Total operating revenues				27,483	26,091	$ 23,814
Advertising costs				346	266	224
Capitalized computer software, net		1,000		1,100	1,000
Computer software depreciation expense				$ 271	246	232
Length of agreements with co-brand, payment, and loyalty partners (in years)				10 years
Number of operating segments | segment				1
Number of reportable segments | segment				1
Workforce Subject to Collective Bargaining Arrangements | Unionized Employees concentration risk
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Full-time employees unionized (as a percent)				82.00%
Latin America
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total operating revenues				$ 798	828	811
North America
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total operating revenues				26,700	25,000	$ 23,000
Other Intangible Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross carrying amount of indefinite-lived intangible assets		296		$ 296	296
Ground property and equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Minimum percentage of cost estimated residual value (as a percent)				0.00%
Maximum percentage of cost estimated as residual value (as a percent)				10.00%
Aircraft Residual Value
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Minimum percentage of cost estimated residual value (as a percent)				14.00%
Maximum percentage of cost estimated as residual value (as a percent)				20.00%
Maximum | Flight equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life (in years)				25 years
Maximum | Ground property and equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life (in years)				30 years
Maximum | Software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life (in years)				15 years
Minimum | Ground property and equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life (in years)				5 years
Minimum | Software
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Useful life (in years)				5 years
Designated as Hedging Instrument
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross amounts offset in the balance sheet		0		$ 0	0
Fuel derivative contracts
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Collateral deposits		50		22	50
Fuel derivative contracts | Other assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross amounts offset in the balance sheet		35		18	35
Fuel derivative contracts | Other assets | Designated as Hedging Instrument
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross amounts offset in the balance sheet		0		0	0
Interest Rate Swap
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Collateral deposits		0		0	0
Interest Rate Swap | Other assets | Designated as Hedging Instrument
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross amounts offset in the balance sheet		$ 0		$ 0	$ 0