REVENUE RECOGNITION - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred revenue recognized	$ 120
Deferred revenue refund payments	13
Payments received from travelers	329
Liabilities for loyalty program incentives	87		$ 73
Reduction in loyalty program liability		$ (27)
Deferred Merchant Bookings
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred revenue in deferred merchant bookings	$ 345		$ 149

Contract With Customer, Liability, Cancellation Refunds

No definition available.

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- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

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- Definition

Value of deferred revenue or cost to provide products or services, which is expected to be recognized in income or incurred within one year or the normal operating cycle, if longer, resulting from customer loyalty program. Excludes liability associated with frequent flier programs. Includes liability associated with customer loyalty programs for other businesses, for example, but is not limited to, hotels, supermarkets, credit card companies, automobile rental companies, and book sellers.

+ References

No definition available.

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- Definition

Increase (decrease) in the liability arising from revenue deferred or cost to provide future products or services resulting from customer loyalty program. Excludes liability associated with frequent flier programs. Includes liability associated with customer loyalty programs for other businesses, for example, but not limited to, hotels, supermarkets, credit card companies, automobile rental companies, and book sellers.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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- Definition

Cash receipts from customers during the current period which are usually for sales of goods and services.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 25
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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.

+ References

No definition available.

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