GENERAL AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Passenger, Mainline	$ 796	$ 723
Passenger, Regional	182	173
Total passenger revenue	978	896
Freight and mail	26	24
Other - net	129	119
Total Operating Revenues	1,133	1,039
Scenario, Previously Reported [Member]
Passenger, Mainline		764
Passenger, Regional		186
Total passenger revenue		950
Freight and mail		24
Other - net		65
Total Operating Revenues		$ 1,039