MILEAGE PLAN (DETAILS) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Mileage Plan [Line Items]
Accrued Liabilities, Current	$ 491.0		$ 491.0		$ 501.2
Deferred Air Traffic Revenue Noncurrent	394.0		394.0		403.5
Other Liabilities, Noncurrent	170.3		170.3		123.0
Passenger Revenue	1,100.8	977.3	2,993.9	2,615.5
Other Revenue, Net	67.4	61.3	195.7	177.8
Total Operating Revenues	1,198.1	1,068.0	3,273.5	2,873.8
Liabilities From Mileage Plan [Member]
Mileage Plan [Line Items]
Accrued Liabilities, Current	274.7		274.7		278.0
Deferred Air Traffic Revenue Noncurrent	375.2		375.2		382.1
Other Liabilities, Noncurrent	14.8		14.8		13.8
Liabilities	664.7		664.7		673.9
Revenue From Mileage Plan [Member]
Mileage Plan [Line Items]
Passenger Revenue	51.7	49.9	156.2	142.0
Other Revenue, Net	51.0	47.5	148.2	138.1
Total Operating Revenues	$ 102.7	$ 97.4	$ 304.4	$ 280.1