Operating Leases - Aircraft (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) aircraft engine	Dec. 31, 2022 USD ($) engine aircraft	Dec. 31, 2021 USD ($) aircraft engine	Sep. 30, 2021 aircraft	Jun. 30, 2021 aircraft	May 31, 2021 aircraft
Lessee, Lease, Description [Line Items]
Gains recognized on sale-leaseback transactions | $	$ 147	$ 87	$ 60
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
A319, To Be Returned In Q2
Lessee, Lease, Description [Line Items]
Charge included as a component of rent expense | $			$ 10
A320neo
Lessee, Lease, Description [Line Items]
Lessee, Operating Leases, Number Of Leases In Period	10	0	0
Aircraft and spare engines
Lessee, Lease, Description [Line Items]
Number of leases	136
Aircraft and spare engines | Minimum
Lessee, Lease, Description [Line Items]
Remaining lease terms	1 year
Aircraft and spare engines | Maximum
Lessee, Lease, Description [Line Items]
Remaining lease terms	12 years
Aircraft and spare engines | A-320 | Aircraft Sale Leaseback
Lessee, Lease, Description [Line Items]
Number of sale-leaseback transactions	11	13	13
Aircraft Engine
Lessee, Lease, Description [Line Items]
Number of leases | engine	35
Number of engines dependent on usage-based metrics | engine	14
Aircraft Engine | Aircraft Sale Leaseback
Lessee, Lease, Description [Line Items]
Number of sale-leaseback transactions | engine	4	4	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 | $	$ 147	$ 87	$ 60