Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in AOCI on derivatives (effective portion)	$ 38		$ (2)
(Gain) loss reclassified from AOCI into income (effective portion)(a)	121	[1]	85	[1]
(Gain) loss recognized in income on derivatives (ineffective portion)(b)	11	[2]	43	[2]
Fuel derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in AOCI on derivatives (effective portion)	52	[3]	(19)	[3]
(Gain) loss reclassified from AOCI into income (effective portion)(a)	103	[1],[3]	101	[1],[3]
(Gain) loss recognized in income on derivatives (ineffective portion)(b)	10	[2]	43	[2]
Fuel derivatives | Not Designated as Hedging Instrument | Other Nonoperating Income Expense
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in income on derivatives	(100)		(264)
Interest rate derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in AOCI on derivatives (effective portion)	(14)	[3]	17	[3]
(Gain) loss reclassified from AOCI into income (effective portion)(a)	18	[1],[3]	(16)	[1],[3]
(Gain) loss recognized in income on derivatives (ineffective portion)(b)	$ 1	[2]	$ 0	[2]

[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