DERIVATIVE INSTRUMENTS - BALANCE SHEET CLASSIFICATION (DETAILS) (USD $) In Millions, unless otherwise specified	3 Months Ended									3 Months Ended
	Mar. 31, 2012	Mar. 31, 2012 Fuel hedge contracts [Member] Derivative Instruments Not Designated as Hedges [Member]	Dec. 31, 2011 Fuel hedge contracts [Member] Derivative Instruments Not Designated as Hedges [Member]	Mar. 31, 2012 Fuel hedge contracts [Member] Derivative Instruments Not Designated as Hedges [Member] Fuel hedge contracts, noncurrent assets [Member]	Dec. 31, 2011 Fuel hedge contracts [Member] Derivative Instruments Not Designated as Hedges [Member] Fuel hedge contracts, noncurrent assets [Member]	Mar. 31, 2012 Interest rate swaps agreements [Member] Derivative Instruments Designated as Hedges [Member] Other accrued liabilities [Member]	Dec. 31, 2011 Interest rate swaps agreements [Member] Derivative Instruments Designated as Hedges [Member] Other accrued liabilities [Member]	Mar. 31, 2012 Interest rate swaps agreements [Member] Derivative Instruments Designated as Hedges [Member] Other liabilities [Member]	Dec. 31, 2011 Interest rate swaps agreements [Member] Derivative Instruments Designated as Hedges [Member] Other liabilities [Member]	Mar. 31, 2012 Interest rate swaps agreements [Member] Derivative Instruments Designated as Hedges [Member] Gains (losses) in AOCL [Member]	Mar. 31, 2011 Interest rate swaps agreements [Member] Derivative Instruments Designated as Hedges [Member] Gains (losses) in AOCL [Member]
Derivatives, Fair Value [Line Items]
Document Period End Date	Mar. 31, 2012
Derivative Assets, Current		$ 58.7	$ 46.7
Derivative Assets, Noncurrent				72.8	70.2
Derivative Liabilities, Current		0	(10.3)			(5.2)	(5.2)
Derivative Liabilities, Noncurrent								(20.4)	(23.6)
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	5.2
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net										$ 3.2	$ (20.0)