Derivatives and Risk Management - Hedge Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Designated as hedges | Foreign currency exchange contracts | Passenger
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) reclassified from AOCI to Earnings	$ 0	$ (1)	$ 0	$ (4)
Designated as hedges | Foreign currency exchange contracts | Other comprehensive income
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized	0	4	0	4
Not designated as hedges
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized	49	(12)	20	(97)
Not designated as hedges | Foreign currency exchange contracts | Unrealized gain/(loss) on investments, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized	18	(19)	25	(12)
Not designated as hedges | Fuel hedge contracts | Aircraft fuel and related taxes
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized	$ 31	$ 7	$ (5)	$ (85)