For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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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.

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Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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Amount of cash outflow to customers for refund payments of revenue that was previously reported as deferred or unearned revenue.

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Amount of revenue recognized that was previously reported as deferred or unearned revenue.

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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.

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

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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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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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 RECOGNITION - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ 15,953,078		$ 15,953,078		$ 14,127,408	$ 13,938,869
Reduction in customer incentive liability			27,000
Customer incentive liability	80,600		80,600			104,700
Revenues	3,537,094	$ 3,024,556	6,465,295	$ 5,443,960
Deferred revenue for merchant revenue transactions	293,000		293,000			$ 151,200
Revenue recognized related to the deferred revenue balance			97,600
Deferred Revenue, Refund Payments			9,100
Cash payments received from travelers reservations			287,300
Difference between Revenue Guidance in Effect before and after Topic 606 \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ (139,366)		$ (139,366)		188,539
Deferred revenue for merchant revenue transactions					$ (32,400)
Sales Revenue, Net [Member] \| Product Concentration Risk [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Concentration Risk, Percentage	86.00%		86.00%