SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) pilot in Thousands, $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2022 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) pilot	Dec. 31, 2022 USD ($) aircraft	Dec. 31, 2021 USD ($) aircraft	Dec. 31, 2020 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reimbursement costs	$ 390	$ 55
Accrued expense on settlement			$ 107
Net income (loss)			465	$ 539	$ 977
Loss on extinguishment			0	193	28
Payroll support and voluntary employee programs, net			0	0	2,960
Other (gains) losses, net			62	(12)	50
Stockholders' equity attributable to parent	10,687		10,515	10,687	10,414	$ 8,876
Impairment charges				$ 28	$ 12
Impaired of assets to be retired			0
Number of aircraft under accelerated retirement | aircraft				10	8
Total operating revenues			26,091	$ 23,814	$ 15,790
Advertising costs			266	224	185
Capitalized computer software, net	928		1,000	928
Computer software depreciation expense			$ 246	232	213
Number of pilots that voted to ratify contract extension | pilot			11
Contract extension (in years)			5 years
Length of agreements with co-brand, payment, and loyalty partners (in years)			10 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
Unionized Employees concentration risk | Workforce Subject to Collective Bargaining Arrangements
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Full-time employees unionized (as a percent)			83.00%
Unionized Employees concentration risk | Number of Employees, Total
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Full-time employees unionized (as a percent)			65.00%
Latin America
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total operating revenues			$ 828	811	475
North America
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total operating revenues			25,000	23,000	15,300
Other Intangible Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross carrying amount of indefinite-lived intangible assets	296		$ 296	296
Aircraft Residual Value
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Maximum percentage of cost estimated as residual value (as a percent)			20.00%
Minimum percentage of cost estimated residual value (as a percent)			13.00%
Ground property and equipment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Maximum percentage of cost estimated as residual value (as a percent)			10.00%
Minimum percentage of cost estimated residual value (as a percent)			0.00%
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
Fuel derivative contracts
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Collateral deposits	106		$ 50	106
Fuel derivative contracts | Other assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross amounts offset in the balance sheet	0		35	0
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 derivatives
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Collateral deposits	0		0	0
Interest rate derivatives | 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
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity attributable to parent	16,261		16,297	16,261	15,774	14,777
Accumulated other comprehensive income (loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity attributable to parent	$ 344		$ 0	$ 344	388	(105)
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity attributable to parent					(245)	0
Cumulative Effect, Period of Adoption, Adjustment | Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity attributable to parent					$ 55	20
Cumulative Effect, Period of Adoption, Adjustment | Accumulated other comprehensive income (loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity attributable to parent						$ (20)