REVENUE - Loyalty Program Revenue (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 3,137	$ 2,232
Mileage Plan Revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	523	412
Passenger \| Mileage Plan Revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	316	248
Mileage plan other revenue \| Mileage Plan Revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 207	$ 164

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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- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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