GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - RECLASSIFICATIONS (DETAILS) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Passenger, Mainline	$ 3,284	$ 2,995	$ 2,595
Passenger, Regional	746	713	671
Total passenger revenue	4,030	3,708	3,266
Freight and mail	111	109	106
Other - net	516	501	460
Total Operating Revenues	4,657	4,318	3,832
Scenario, Previously Reported [Member]
Passenger, Mainline		3,176	2,763
Passenger, Regional		775	726
Total passenger revenue		3,951	3,489
Freight and mail		109	106
Other - net		258	237
Total Operating Revenues		$ 4,318	$ 3,832