Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)		$ (114)	$ (34)	$ (74)	$ 19
(Gain) Loss reclassified from AOCI into income (effective portion)	[1]	152	44	349	93
(Gain) Loss recognized in income on derivatives (ineffective portion)	[2]	(4)	(3)	0	(17)
Fuel derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	[3]	(116)	(33)	(80)	16
(Gain) Loss reclassified from AOCI into income (effective portion)	[1],[3]	149	41	344	87
(Gain) Loss recognized in income on derivatives (ineffective portion)	[2]	(3)	(2)	1	(15)
Interest rate derivatives | Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) Loss recognized in AOCI on derivatives (effective portion)	[3]	2	(1)	6	3
(Gain) Loss reclassified from AOCI into income (effective portion)	[1],[3]	3	3	5	6
(Gain) Loss recognized in income on derivatives (ineffective portion)	[2]	(1)	(1)	(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		$ (88)	$ 71	$ (12)	$ 91

[1] Amounts related to fuel derivative contracts and interest rate derivatives, which are included in Fuel and oil and Interest expense, respectively.

[2] Amounts are included in Other (gains) losses, net.

[3] Net of tax