DERIVATIVE INSTRUMENTS - BALANCE SHEET CLASSIFICATION (DETAILS) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	$ 5.2
Fuel hedge contracts [Member] | Derivatvie Instruments Not Designated as Hedges [Member] | Fuel hedge contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	46.7	61.4
Derivative Liabilities, Current	10.3	0
Fuel hedge contracts [Member] | Derivatvie Instruments Not Designated as Hedges [Member] | Fuel hedge contracts, noncurrent assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Noncurrent	70.2	69.9
Interest rate swaps agreements [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Current	(5.2)	(6.0)
Interest rate swaps agreements [Member] | Derivatvie Instruments Designated as Hedges [Member] | Other accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Current	(5.2)	(6.0)
Interest rate swaps agreements [Member] | Derivatvie Instruments Designated as Hedges [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Noncurrent	(23.6)	(2.8)
Interest rate swaps agreements [Member] | Derivatvie Instruments Designated as Hedges [Member] | Gains (losses) in AOCL [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Noncurrent	$ (20.0)	$ 11.2