COMMITMENTS (DETAILS) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012 carriers	Sep. 30, 2011	Sep. 30, 2012 carriers	Sep. 30, 2011
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Rent Expense	$ 68.8	$ 69.4	$ 206.7	$ 207.9
Airline, Capacity Purchase Arrangements, Carriers	3		3
Airline, Capacity Purchase Arrangements, Percent	100.00%		100.00%
Aircraft Commitments [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Remainder of 2012	113.7		113.7
2013	351.2		351.2
2014	215.7		215.7
2015	49.1		49.1
2016	18.4		18.4
Thereafter	36.8		36.8
Total	784.9		784.9
Capacity Purchase Agreements [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Remainder of 2012	4.3		4.3
2013	17.4		17.4
2014	17.7		17.7
2015	18.0		18.0
2016	18.3		18.3
Thereafter	26.5		26.5
Total	102.2		102.2
Engine Maintenance [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Remainder of 2012	10.4		10.4
2013	31.7		31.7
2014	25.3		25.3
2015	9.2		9.2
2016	0		0
Thereafter	0		0
Total	76.6		76.6
Aircraft Leases [Member]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Remainder of 2012	16.9		16.9
2013	141.6		141.6
2014	126.1		126.1
2015	104.4		104.4
2016	81.9		81.9
Thereafter	130.7		130.7
Total	601.6		601.6
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Operating Leases, Number of Units (in Aircraft)	63		63
Facility Leases [Member]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Remainder of 2012	17.8		17.8
2013	47.2		47.2
2014	42.1		42.1
2015	31.7		31.7
2016	23.0		23.0
Thereafter	157.8		157.8
Total	319.6		319.6
Assets Leased to Others [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Operating Leases, Number of Units (in Aircraft)	14		14
B737 [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Options to Purchase Additional (in Aircraft)	39		39
B737-700 [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Sale Leaseback Transaction, Deferred Gain, Net	$ 3.2		$ 3.2
B737-700 [Member] | Aircraft Leases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Sale Leaseback Leases, Number of Units (in Aircraft)	3		3
B737-800 [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Operating Leases, Number of Units (in Aircraft)	6.0		6.0
Committed to Purchase (in Aircraft)	3		3
B737-900ER [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Committed to Purchase (in Aircraft)	22		22
Q400 [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Number to be Aircraft Sold	2		2
Options to Purchase Additional (in Aircraft)	10		10