COMMITMENTS (DETAILS) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012 carriers	Jun. 30, 2011	Jun. 30, 2012 carriers	Jun. 30, 2011
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Rent Expense	$ 67.9	$ 69.4	$ 137.9	$ 138.5
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	181.8		181.8
2013	333.2		333.2
2014	194.6		194.6
2015	48.0		48.0
2016	18.4		18.4
Thereafter	36.8		36.8
Total	812.8		812.8
Capacity Purchase Agreements[Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Remainder of 2012	9.7		9.7
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	107.6		107.6
Engine Maintenance [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Remainder of 2012	20.9		20.9
2013	31.9		31.9
2014	26.4		26.4
2015	10.1		10.1
2016	0		0
Thereafter	0		0
Total	89.3		89.3
Aircraft Leases [Member]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Remainder of 2012	41.8		41.8
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	626.5		626.5
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	31.8		31.8
2013	42.5		42.5
2014	38.5		38.5
2015	27.0		27.0
2016	17.2		17.2
Thereafter	137.9		137.9
Total	294.9		294.9
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]
Option 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
Commited to Purchase (in Aircraft)	3		3
Number of Aircraft Purchased	1		1
B737-900ER [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Commited to Purchase (in Aircraft)	22		22
Q400 [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Number to be Aircraft Sold	2		2
Option to Purchase Additional (in Aircraft)	10		10
Number of Aircraft Purchased	2		2