Number of Partner AIrlines

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Percent of Mileage Breakage

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Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer.

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Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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Total costs of sales and operating expenses for the period.

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Value of revenue deferred or cost to provide future services associated with points or miles outstanding and awards that expect to be redeemed through customer loyalty programs and the value of transportation services sold but as yet used by the passenger. Used to reflect the current portion of the liability (within one year or within the normal operating cycle if longer).

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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.

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REVENUE FROM CONTRACTS WITH CUSTOMERS - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) airline	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Deferred Revenue Arrangement [Line Items]
Number of airline partners \| airline			15
Breakage rate	17.40%	17.40%	17.40%	17.40%
Air traffic liability	$ 950		$ 950		$ 806
Receivable	422		422		341
Contract cost recognized	57	$ 61	166	$ 183
Prepaid Expenses and Other Current Assets [Member]
Deferred Revenue Arrangement [Line Items]
Contract costs	27		27		24
Mileage Plan Revenue [Member]
Deferred Revenue Arrangement [Line Items]
Receivable	106		106		$ 101
Mileage Plan Revenue [Member] \| Mileage plan other revenue [Member]
Deferred Revenue Arrangement [Line Items]
Contract liability revenue recognized			(66)	(54)
Passenger Revenue [Member]
Deferred Revenue Arrangement [Line Items]
Contract liability revenue recognized	$ 27	$ 23	$ 540	$ 543