DERIVATIVE INSTRUMENTS - BALANCE SHEET CLASSIFICATION (DETAILS) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Accumulated other comprehensive (loss)	$ (305)	$ (310)
Posted collateral	5	3
Fuel hedge contracts [Member] \| Derivative Instruments Not Designated as Hedges [Member] \| Fuel hedge contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	3	3
Fuel hedge contracts [Member] \| Derivative Instruments Not Designated as Hedges [Member] \| Fuel hedge contracts, noncurrent assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Noncurrent	2	4
Interest rate swaps agreements [Member] \| Derivative Instruments Designated as Hedges [Member] \| Other accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Current	(6)	(6)
Interest rate swaps agreements [Member] \| Derivative Instruments Designated as Hedges [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities, Noncurrent	(15)	(13)
Interest rate swaps agreements [Member] \| Derivative Instruments Designated as Hedges [Member] \| Gains (losses) in AOCL [Member]
Derivatives, Fair Value [Line Items]
Accumulated other comprehensive (loss)	(21)	(19)
Derivative Gain (Loss) in Accumulated Other Comprehensive Loss To Be Reclassified Within Next Twelve Months	$ (6)

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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-Publisher SEC

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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The estimated net amount of unrealized gains or losses on price risk cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

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