DERIVATIVE INSTRUMENTS - BALANCE SHEET CLASSIFICATION (DETAILS) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Accumulated other comprehensive loss	$ 436	$ 390
Derivative, Collateral, Right to Reclaim Cash	15	1	0
Fuel hedge contracts [Member] | Derivative Instruments Not Designated as Hedges [Member] | Fuel Hedge Contracts, Current [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	26	47
Fuel hedge contracts [Member] | Derivative Instruments Not Designated as Hedges [Member] | Fuel Hedge Contracts, Noncurrent [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Noncurrent	39	70
Fuel hedge contracts [Member] | Derivative Instruments Not Designated as Hedges [Member] | Other Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Current	(1)	(10)
Interest rate swaps agreements [Member] | Derivative Instruments Designated as Hedges [Member] | Other Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Current	(6)	(5)
Interest rate swaps agreements [Member] | Derivative Instruments Designated as Hedges [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Noncurrent	(27)	(24)
Interest rate swaps agreements [Member] | Derivative Instruments Designated as Hedges [Member] | Accumulated Other Comprehensive Loss [Member]
Derivatives, Fair Value [Line Items]
Accumulated other comprehensive loss	$ (33)	$ (29)