Derivatives and Risk Management - Not Designated Hedge Gains (Losses) (Details) - Not designated as hedges - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized	$ 54	$ (31)	$ 48
Foreign currency exchange contracts | Gain/(loss) on investments, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized	(31)	10	(4)
Fuel hedge contracts | Aircraft fuel and related taxes
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivatives recognized	$ 85	$ (41)	$ 52