DERIVATIVE INSTRUMENTS - FAIR VALUE OF HEDGE POSITIONS (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
Derivative [Line Items]
Net cash received (paid) to for new positions and settlements	$ (11.1)	$ 9.6	$ (17.5)	$ 15.0
B737-800 [Member]
Derivative [Line Items]
Operating Leases, Number of Units (in Aircraft)	6.0		6.0
Not Designated as Hedging Instrument [Member] | Fuel hedge contracts [Member]
Derivative [Line Items]
Fuel hedge contracts outstanding (in barrels)	10,300,000		10,300,000