Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	$ (119)		$ 178		$ (105)		$ 204
(Gain) Loss reclassified from AOCI into income (effective portion)	2	[1]	41	[1]	6	[1]	72	[1]
(Gain) Loss recognized in income on derivatives (ineffective portion)	(28)	[2]	2	[2]	(42)	[2]	11	[2]
Fuel derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	(122)	[3]	189	[3]	(110)	[3]	218	[3]
(Gain) Loss reclassified from AOCI into income (effective portion)	(1)	[1],[3]	37	[1],[3]	(1)	[1],[3]	63	[1],[3]
(Gain) Loss recognized in income on derivatives (ineffective portion)	(28)	[2]	3	[2]	(41)	[2]	12	[2]
Interest rate derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	3	[3]	(11)	[3]	5	[3]	(14)	[3]
(Gain) Loss reclassified from AOCI into income (effective portion)	3	[1],[3]	4	[1],[3]	7	[1],[3]	9	[1],[3]
(Gain) Loss recognized in income on derivatives (ineffective portion)	0	[2]	(1)	[2]	(1)	[2]	(1)	[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	$ 16		$ 32		$ (40)		$ (28)

[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