Leases - Narrative (Details)		3 Months Ended	12 Months Ended
	Dec. 05, 2022 USD ($) aircraft	Jun. 30, 2020 USD ($) aircraft	Dec. 31, 2022 USD ($) aircraft	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Proceeds from sale-leaseback transactions			$ 0	$ 0	$ 815,000,000
Gain on sale-leaseback transactions			0	0	222,000,000
Capital expenditures			3,924,000,000	505,000,000	515,000,000
Payments of long-term debt and finance lease obligations			2,437,000,000	612,000,000	$ 839,000,000
Total lease obligations			$ 189,000,000	$ 459,000,000
Airport-Related
Lessee, Lease, Description [Line Items]
Term of lease contract (in years)			38 years
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		$ 410,000,000
Gain on sale-leaseback transactions		$ 69,000,000
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		$ 405,000,000
Gain on sale-leaseback transactions		$ 153,000,000
Boeing 737-700 | Aircraft
Lessee, Lease, Description [Line Items]
Number of aircrafts to be purchased | aircraft	39		8
Number of aircrafts purchased | aircraft			31
Capital expenditures	$ 365,000,000
Payments of long-term debt and finance lease obligations			$ 191,000,000
Total lease obligations			$ 174,000,000
Number of leased aircrafts | aircraft			28
Gain on sale of aircrafts			$ 0
Minimum | Aircraft
Lessee, Lease, Description [Line Items]
Renewal term (in years)			3 months
Minimum | Other
Lessee, Lease, Description [Line Items]
Renewal term (in years)			6 months
Minimum | Airport-Related
Lessee, Lease, Description [Line Items]
Renewal term (in years)			1 year
Maximum | Aircraft
Lessee, Lease, Description [Line Items]
Term of contract (in years)			11 years
Renewal term (in years)			3 years
Maximum | Other
Lessee, Lease, Description [Line Items]
Term of contract (in years)			4 years
Renewal term (in years)			3 years
Maximum | Airport-Related
Lessee, Lease, Description [Line Items]
Renewal term (in years)			11 years