GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - MILEAGE PLAN (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Mileage Plan [Line Items]
Other accrued liabilities	$ 878	$ 661
Other liabilities	417	362
Deferred revenue	640	431
Deferred revenue from Mileage Plan awards issued but not yet flown	43	37
Passenger revenues	5,006	4,793	$ 4,579
Other-net revenues	817	697	675
Total Operating Revenues	5,931	5,598	5,368
Revenue From Mileage Plan [Member]
Mileage Plan [Line Items]
Passenger revenues	293	267	246
Other-net revenues	429	329	295
Total Operating Revenues	722	596	541
Commission revenue	329	280	$ 261
Liabilities From Mileage Plan [Member]
Mileage Plan [Line Items]
Other accrued liabilities	484	368
Other liabilities	21	19
Deferred revenue	638	427
Liabilities	$ 1,143	$ 814