Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	$ 26		$ (138)
(Gain) Loss reclassified from AOCI into income (effective portion)	31	[1]	27	[1]
(Gain) Loss recognized in income on derivatives (ineffective portion)	10	[2]	32	[2]
Fuel derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	29	[3]	(136)	[3]
(Gain) Loss reclassified from AOCI into income (effective portion)	26	[1],[3]	23	[1],[3]
(Gain) Loss recognized in income on derivatives (ineffective portion)	10	[2]	32	[2]
Interest rate derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	(3)	[3]	(2)	[3]
(Gain) Loss reclassified from AOCI into income (effective portion)	5	[1],[3]	4	[1],[3]
(Gain) Loss recognized in income on derivatives (ineffective portion)	0	[2]	0	[2]
Other Nonoperating Income Expense [Member] | Fuel derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in income on derivatives	$ 61		$ (208)

[1] Amounts related to fuel derivative contracts and interest rate derivatives are included in Fuel and oil and Interest expense, respectively.

[2] Amounts are included in Other (gains) losses, net.

[3] Net of tax