MILEAGE PLAN MILEAGE PLAN (DETAILS) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Mileage Plan [Line Items]
Other accrued liabilities	$ 558.5		$ 558.5		$ 513.3
Deferred revenue	414.0		414.0		410.2
Other liabilities	204.8		204.8		176.7
Total passenger revenue	1,050.3	953.2	1,946.5	1,774.1
Other - net	132.3	127.9	251.0	247.3
Total Operating Revenues	1,213.2	1,110.2	2,252.5	2,075.4
Liabilities From Mileage Plan [Member]
Mileage Plan [Line Items]
Other accrued liabilities	289.1		289.1		271.4
Deferred revenue	397.8		397.8		392.2
Other liabilities	17.2		17.2		16.9
Liabilities	704.1		704.1		680.5
Revenue From Mileage Plan [Member]
Mileage Plan [Line Items]
Total passenger revenue	48.2	54.2	90.8	104.5
Other - net	55.2	51.6	102.7	97.2
Total Operating Revenues	$ 103.4	$ 105.8	$ 193.5	$ 201.7