Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)		$ 318	$ 212	$ 336	$ 106
(Gain) Loss reclassified from AOCI into income (effective portion)	[1]	82	8	175	13
(Gain) Loss recognized in income on derivatives (ineffective portion)	[2]	0	9	(17)	(34)
Fuel derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	[3]	315	214	330	104
(Gain) Loss reclassified from AOCI into income (effective portion)	[1],[3]	79	4	166	3
(Gain) Loss recognized in income on derivatives (ineffective portion)	[2]	0	11	(15)	(31)
Interest rate derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	[3]	3	(2)	6	2
(Gain) Loss reclassified from AOCI into income (effective portion)	[1],[3]	3	4	9	10
(Gain) Loss recognized in income on derivatives (ineffective portion)	[2]	0	(2)	(2)	(3)
Other Nonoperating Income Expense | Fuel derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in income on derivatives		$ 239	$ 39	$ 330	$ (1)

[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