MILEAGE PLAN (DETAILS) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Mileage Plan [Line Items]
Accrued Liabilities, Current	$ 544.0		$ 544.0		$ 501.2
Deferred Air Traffic Revenue Noncurrent	386.7		386.7		403.5
Other Liabilities, Noncurrent	148.6		148.6		123.0
Passenger Revenue	1,014.2	885.8	1,893.1	1,638.2
Other Revenue, Net	66.9	62.3	128.3	116.5
Total Operating Revenues	1,110.2	976.2	2,075.4	1,805.8
Liabilities From Mileage Plan [Member]
Mileage Plan [Line Items]
Accrued Liabilities, Current	286.1		286.1		278.0
Deferred Air Traffic Revenue Noncurrent	367.0		367.0		382.1
Other Liabilities, Noncurrent	14.1		14.1		13.8
Liabilities	667.2		667.2		673.9
Revenue From Mileage Plan [Member]
Mileage Plan [Line Items]
Passenger Revenue	54.2	51.0	104.5	92.1
Other Revenue, Net	51.6	48.6	97.2	90.6
Total Operating Revenues	$ 105.8	$ 99.6	$ 201.7	$ 182.7