GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - RECENTLY ISSUED ACCOUNTING PRONOUNCEMENTS (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue	$ 699	$ 640
Decrease in air traffic liability	937	849
Overall impact to equity	4,454	3,568
Liabilities From Mileage Plan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue	$ 699	638
Minimum [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]]] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in air traffic liability		(70)
Overall impact to equity			$ 165
Minimum [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]]] | Accounting Standards Update 2014-09 [Member] | Liabilities From Mileage Plan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue		345
Maximum [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]]] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in air traffic liability		(80)
Overall impact to equity			$ 175
Maximum [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]]] | Accounting Standards Update 2014-09 [Member] | Liabilities From Mileage Plan [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue		$ 365