Financial Derivative Instruments - (Gain) Loss by Hedging Relationship (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Cash Flow Hedging
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in AOCI on derivatives, net of tax	$ (147)	$ (186)	$ (804)	$ (279)
Cash Flow Hedging | Fuel derivative contracts
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in AOCI on derivatives, net of tax	(140)	(192)	(792)	(275)
Cash Flow Hedging | Interest rate derivative contracts
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in AOCI on derivatives, net of tax	(7)	6	(12)	(4)
Not Designated as Hedging Instrument | Fuel derivative contracts | Other Nonoperating Income (Expense)
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss recognized in income on derivatives	$ (20)	$ (12)	$ 15	$ (16)