DERIVATIVE INSTRUMENTS - FAIR VALUE OF HEDGE POSITIONS (Details) gallons in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) gallons aircraft	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Derivative [Line Items]
Net cash received (paid) to for new positions and settlements | $	$ (17)	$ (9)	$ 5
B737-800 [Member]
Derivative [Line Items]
Capital Leased Assets, Number of B737-800 Aircraft | aircraft	6
Not Designated as Hedging Instrument [Member] | Fuel hedge contracts [Member]
Derivative [Line Items]
Fuel hedge contracts outstanding (in gallons) | gallons	273