Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	$ (103)		$ (160)		$ 101		$ (6)
(Gain) Loss reclassified from AOCI into income (effective portion)	28	[1]	29	[1]	102	[1]	89	[1]
(Gain) Loss recognized in income on derivatives (ineffective portion)	15	[2]	4	[2]	26	[2]	44	[2]
Fuel derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	(105)	[3]	(167)	[3]	113	[3]	(24)	[3]
(Gain) Loss reclassified from AOCI into income (effective portion)	24	[1],[3]	25	[1],[3]	88	[1],[3]	76	[1],[3]
(Gain) Loss recognized in income on derivatives (ineffective portion)	15	[2]	4	[2]	27	[2]	44	[2]
Interest rate derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	2	[3]	7	[3]	(12)	[3]	18	[3]
(Gain) Loss reclassified from AOCI into income (effective portion)	4	[1],[3]	4	[1],[3]	14	[1],[3]	13	[1],[3]
(Gain) Loss recognized in income on derivatives (ineffective portion)	0	[2]	0	[2]	(1)	[2]	0	[2]
Other Nonoperating Income Expense | Fuel derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in income on derivatives	$ (93)		$ (32)		$ (122)		$ (200)

[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