Leases - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) aircraft	Dec. 31, 2021 USD ($) aircraft	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 09, 2012 aircraft
Lessee, Lease, Description [Line Items]
Term of lease contract (in years)		9 years
Sublease income - 2022		$ 17
Sublease income - 2023		7
Sublease income - 2024		1
Proceeds from sale-leaseback transactions		0	$ 815	$ 0
Gain on sale-leaseback transactions		$ 0	$ 222	$ 0
B-717-200
Lessee, Lease, Description [Line Items]
Number of aircrafts subject or available for operating lease | aircraft		14			88
B-737-800
Lessee, Lease, Description [Line Items]
Number of aircrafts available for operating lease | aircraft	10
Term of lease contract (in years)	10 years
Proceeds from sale-leaseback transactions	$ 405
Gain on sale-leaseback transactions	$ 153
B-737-8 Max
Lessee, Lease, Description [Line Items]
Number of aircrafts available for operating lease | aircraft	10
Term of lease contract (in years)	13 years
Proceeds from sale-leaseback transactions	$ 410
Gain on sale-leaseback transactions	$ 69
Minimum | Aircraft
Lessee, Lease, Description [Line Items]
Term of contract (in years)		1 month
Renewal term (in years)		3 months
Minimum | Other
Lessee, Lease, Description [Line Items]
Term of contract (in years)		3 months
Renewal term (in years)		6 months
Minimum | Airport-Related
Lessee, Lease, Description [Line Items]
Renewal term (in years)		1 year
Lease term (in months and years)		1 month
Maximum | Aircraft
Lessee, Lease, Description [Line Items]
Term of contract (in years)		12 years
Renewal term (in years)		3 years
Maximum | Other
Lessee, Lease, Description [Line Items]
Term of contract (in years)		5 years
Renewal term (in years)		3 years
Maximum | Airport-Related
Lessee, Lease, Description [Line Items]
Renewal term (in years)		10 years
Lease term (in months and years)		39 years