Fuel - Effects of Derivative Instruments Gains and Losses (Details) (Cash Flow Hedging, USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Other Comprehensive Income (OCI) on Derivatives (Effective Portion)	$ 0		$ (35)		$ 7		$ 20
Amount of Gain or (Loss) Recognized from AOCL into Income (Effective Portion)	0		18		25		75
Amount of Gain or (Loss) Recognized in Income on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	[1]	(5)	[1]	(3)	[1]	(14)	[1]
Fuel Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Other Comprehensive Income (OCI) on Derivatives (Effective Portion)	0		(35)		7		20
Fuel Contracts | Fuel Expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized from AOCL into Income (Effective Portion)	0		18		25		75
Amount of Gain or (Loss) Recognized in Income on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	$ 0	[1]	$ (5)	[1]	$ (3)	[1]	$ (14)	[1]

[1] No portion of the gain or (loss) was excluded from the assessment of hedge effectiveness for the periods then ended.