MILEAGE PLAN MILEAGE PLAN (DETAILS) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Mileage Plan [Line Items]
Other accrued liabilities	$ 537.0		$ 537.0		$ 513.3
Deferred revenue	423.4		423.4		410.2
Other liabilities	213.0		213.0		176.7
Total passenger revenue	1,102.7	1,031.7	3,049.2	2,805.8
Other - net	139.9	136.5	390.9	383.8
Total Operating Revenues	1,272.2	1,198.1	3,524.7	3,273.5
Liabilities From Mileage Plan [Member]
Mileage Plan [Line Items]
Other accrued liabilities	292.1		292.1		271.4
Deferred revenue	408.0		408.0		392.2
Other liabilities	17.1		17.1		16.9
Liabilities	717.2		717.2		680.5
Revenue From Mileage Plan [Member]
Mileage Plan [Line Items]
Total passenger revenue	46.6	51.7	137.4	156.2
Other - net	55.6	51.0	158.3	148.2
Total Operating Revenues	$ 102.2	$ 102.7	$ 295.7	$ 304.4