DEBT - Summary of Long-Term Debt (Details) - USD ($)	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Long term debt	$ 24,837,000,000	$ 29,352,000,000
Less: unamortized debt discount, premiums and debt issuance costs	(184,000,000)	(277,000,000)
Less: current portion of long-term debt	(2,973,000,000)	(4,018,000,000)
Long-term debt, net	21,680,000,000	25,057,000,000
Secured Debt \| Equipment Notes
Debt Instrument [Line Items]
Long term debt	$ 12,983,000,000	12,508,000,000
Secured Debt \| Equipment Notes \| Minimum
Debt Instrument [Line Items]
Fixed interest rate	2.70%
Basis spread on variable rate	0.64%
Secured Debt \| Equipment Notes \| Maximum
Debt Instrument [Line Items]
Fixed interest rate	6.51%
Basis spread on variable rate	2.00%
Secured Debt \| MileagePlus Senior Secured Notes
Debt Instrument [Line Items]
Fixed interest rate	6.50%
Long term debt	$ 1,900,000,000	2,660,000,000
Secured Debt \| MileagePlus Term Loan Facility
Debt Instrument [Line Items]
Long term debt	0	2,100,000,000
Secured Debt \| 2026 and 2029 Notes
Debt Instrument [Line Items]
Long term debt	$ 4,000,000,000	4,000,000,000
Secured Debt \| 2026 and 2029 Notes \| Minimum
Debt Instrument [Line Items]
Fixed interest rate	4.38%
Secured Debt \| 2026 and 2029 Notes \| Maximum
Debt Instrument [Line Items]
Fixed interest rate	4.63%
Secured Debt \| 2021 Term Loans
Debt Instrument [Line Items]
Long term debt	$ 0	3,870,000,000
Basis spread on variable rate	2.00%
Secured Debt \| 2024 Term Loans
Debt Instrument [Line Items]
Fixed interest rate	6.63%
Long term debt	$ 2,082,000,000	0
Unsecured \| Notes
Debt Instrument [Line Items]
Fixed interest rate	4.88%
Long term debt	$ 315,000,000	596,000,000
Unsecured \| PSP Notes
Debt Instrument [Line Items]
Fixed interest rate	1.00%
Long term debt	$ 3,181,000,000	3,181,000,000
Basis spread on variable rate	2.00%
Unsecured \| PSP1 Note
Debt Instrument [Line Items]
Aggregate principal amount of debt	$ 1,500,000,000
Term of debt	10 years
Unsecured \| PSP2 Note
Debt Instrument [Line Items]
Aggregate principal amount of debt	$ 900,000,000
Term of debt	10 years
Unsecured \| PSP3 Note
Debt Instrument [Line Items]
Aggregate principal amount of debt	$ 800,000,000
Term of debt	10 years
Unsecured \| Other unsecured debt
Debt Instrument [Line Items]
Long term debt	$ 376,000,000	$ 437,000,000
Unsecured \| Other unsecured debt \| Minimum
Debt Instrument [Line Items]
Fixed interest rate	4.00%
Unsecured \| Other unsecured debt \| Maximum
Debt Instrument [Line Items]
Fixed interest rate	5.75%

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt classified as current. Excludes lease obligation.

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Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt classified as noncurrent. Excludes lease obligation.

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