Derivatives and Risk Management - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Proceeds from derivative instruments					$ 291	$ 429	$ 0
Payments for derivative instruments					451	71	0
Derivative losses					(342)	(1,366)	$ 2,186
Cash flow hedge net gain to be reclassified within twelve months					27
Margin posted due to fair value of hedge contracts		$ 38	$ 119		38	119
Fuel derivative
Derivative [Line Items]
Proceeds from derivative instruments		$ 300	$ 300
Payments for derivative instruments					300
Fuel derivative | Forecast
Derivative [Line Items]
Expected payments for derivative instruments				$ 300
Fuel hedge contract
Derivative [Line Items]
Derivative losses					$ 366	$ 741
Fuel hedge contract | Airline
Derivative [Line Items]
Settlement of derivative contract	$ 455