Operating Leases - Aircraft (Details) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) amendment aircraft	Dec. 31, 2021 USD ($) aircraft aircraftEngine	Dec. 31, 2020 USD ($) aircraftEngine aircraft	Dec. 31, 2019 USD ($) aircraft aircraftEngine	Sep. 30, 2021 aircraft	Jun. 30, 2021 aircraft	May 31, 2021 aircraft	Feb. 28, 2020
Lessee, Lease, Description [Line Items]
Gains recognized on sale-leaseback transactions | $		$ 60	$ 48	$ 107
Number of amendments | amendment	2
Number of aircraft renewed	2
Length of contract	5 years							3 years
Cash flows from operating leases | $	$ (17)	$ 0	$ (17)	$ 0
Number of aircraft terminated							6
A-320
Lessee, Lease, Description [Line Items]
Number of aircraft returned		2
A-319
Lessee, Lease, Description [Line Items]
Number of aircraft terminated		4
Number of aircraft returned					2	2
A-319, To Be Returned Early
Lessee, Lease, Description [Line Items]
Charge included as a component of rent expense | $		$ 10
Aircraft
Lessee, Lease, Description [Line Items]
Number of leases		110
Aircraft | Minimum
Lessee, Lease, Description [Line Items]
Remaining lease terms		3 months
Aircraft | Maximum
Lessee, Lease, Description [Line Items]
Remaining lease terms		12 years
Aircraft | A-320 | Aircraft Sale Leaseback
Lessee, Lease, Description [Line Items]
Number of sale-leaseback transactions		13	9	18
Aircraft Engine
Lessee, Lease, Description [Line Items]
Number of leases | aircraftEngine		21
Number of engines dependent on usage-based metrics | aircraftEngine			7
Aircraft Engine | Aircraft Sale Leaseback
Lessee, Lease, Description [Line Items]
Number of sale-leaseback transactions | aircraftEngine		2	1	2
Aircraft Engine | Minimum
Lessee, Lease, Description [Line Items]
Remaining lease terms		1 month
Aircraft Engine | Maximum
Lessee, Lease, Description [Line Items]
Remaining lease terms		12 years
Aircraft and Aircraft Engines
Lessee, Lease, Description [Line Items]
Gains recognized on sale-leaseback transactions | $		$ 60	$ 48	$ 107
Acquired aircraft and engines through operating leases | $		$ 500	$ 274