Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)		$ 41	$ 52
(Gain) Loss reclassified from AOCI into income (effective portion)	[1]	197	48
(Gain) Loss recognized in income on derivatives (ineffective portion)	[2]	4	(14)
Fuel derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	[3]	36	48
(Gain) Loss reclassified from AOCI into income (effective portion)	[1],[3]	195	45
(Gain) Loss recognized in income on derivatives (ineffective portion)	[2]	4	(13)
Interest rate derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	[3]	5	4
(Gain) Loss reclassified from AOCI into income (effective portion)	[1],[3]	2	3
(Gain) Loss recognized in income on derivatives (ineffective portion)	[2]	0	(1)
Other Nonoperating Income Expense | Fuel derivatives | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in income on derivatives		$ 76	$ 19

[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