FINANCIAL DERIVATIVE INSTRUMENTS - (Gain) Loss by Hedging Relationship (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Fuel derivative contracts
Derivative Instruments, (Gain) Loss
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other (gains) losses, net	Other (gains) losses, net
Cash Flow Hedging
Derivative Instruments, (Gain) Loss
(Gain) Loss recognized in AOCI on derivatives, net of tax	$ 231	$ (508)
Cash Flow Hedging \| Fuel derivative contracts
Derivative Instruments, (Gain) Loss
(Gain) Loss recognized in AOCI on derivatives, net of tax	238	(494)
Cash Flow Hedging \| Interest rate derivatives
Derivative Instruments, (Gain) Loss
(Gain) Loss recognized in AOCI on derivatives, net of tax	(7)	(14)
Not Designated as Hedging Instrument \| Fuel derivative contracts
Derivative Instruments, (Gain) Loss
(Gain) Loss recognized in income on derivatives	$ (17)	$ (41)

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4A

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Indicates line item in statement of income or comprehensive income that includes gain (loss) from derivative.

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4E
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4E

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Amount, before tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-11

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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-SubTopic 10
-Topic 815
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4C

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