SUBSEQUENT EVENT (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
Subsequent Event [Line Items]
Wages and benefits	$ 255.1	$ 245.1	$ 770.6	$ 737.2
Aircraft Commitments [Member]
Subsequent Event [Line Items]
Unrecorded Unconditional Purchase Obligation	784.9		784.9
B737 [Member]
Subsequent Event [Line Items]
Options to Purchase Additional (in Aircraft)	39		39
B737-900ER [Member]
Subsequent Event [Line Items]
Committed to Purchase (in Aircraft)	22		22
Aircraft Agreement [Member] | Aircraft Commitments [Member]
Subsequent Event [Line Items]
Unrecorded Unconditional Purchase Obligation	3,000.0		3,000.0
Aircraft Agreement [Member] | B737 [Member]
Subsequent Event [Line Items]
Additional Commitment to Purchase (in Aircraft)	50		50
Committed to Purchase (in Aircraft)	75		75
Options to Purchase Additional (in Aircraft)	69		69
Aircraft Agreement [Member] | B737-900ER [Member]
Subsequent Event [Line Items]
Committed to Purchase (in Aircraft)	38		38
Aircraft Agreement [Member] | B737 MAX [Member]
Subsequent Event [Line Items]
Committed to Purchase (in Aircraft)	37		37
Tentative Pilot Union Agreement [Member]
Subsequent Event [Line Items]
Wages and benefits			$ 1.0