Leases and Capacity Purchase Agreements - Narrative (Details) $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2021 aircraft	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) aircraft	Dec. 31, 2020 USD ($) aircraft	Dec. 31, 2019 USD ($)	Aug. 31, 2021 USD ($)
Lessee, Lease, Description [Line Items]
Additional leases that have not yet commenced | $			$ 415
Lease terms of additional leases that have not yet commenced (up to)			12 years
Number of aircraft included in flight equipment			7
Number of aircraft qualified for sale recorded as operating lease right-of-use assets and current/long-term obligations			17
Special Facility Revenue Bonds | Secured Debt
Lessee, Lease, Description [Line Items]
Fixed interest rate						4.00%
Special Facility Revenue Bonds | Secured Debt | City of Houston
Lessee, Lease, Description [Line Items]
Aggregate principal amount | $						$ 289
Boeing 787-9 and Boeing 737 MAX
Lessee, Lease, Description [Line Items]
Number of aircraft delivered under sale and leaseback transaction				24
Boeing 787
Lessee, Lease, Description [Line Items]
Number of aircraft acquired with exercised purchase options			6
Boeing 737 MAX
Lessee, Lease, Description [Line Items]
Number of aircraft acquired with exercised purchase options			8
Embraer E175
Lessee, Lease, Description [Line Items]
Number of regional aircraft	38
United Airlines, Inc. | Embraer E175
Lessee, Lease, Description [Line Items]
Long-term purchase commitment, period	12 years
United Airlines, Inc. | Cash Collateralized Letters of Credit
Lessee, Lease, Description [Line Items]
Number of regional aircraft			518
Mainline Aircraft
Lessee, Lease, Description [Line Items]
Number of aircraft subject to operating leases			118
Number of aircraft subject to finance leases			25
Regional Aircraft
Lessee, Lease, Description [Line Items]
Number of aircraft subject to operating leases			282
Number of aircraft subject to finance leases			58
Regional Aircraft | United Airlines, Inc. | Capacity Purchase Agreements
Lessee, Lease, Description [Line Items]
Expenses | $			$ 600	$ 600	$ 1,000
Accounts payable | $			$ 102	$ 68
Minimum | Mainline Aircraft
Lessee, Lease, Description [Line Items]
Initial term of operating leases			1 month
Minimum | Non-Aircraft
Lessee, Lease, Description [Line Items]
Initial term of operating leases			1 month
Maximum | Mainline Aircraft
Lessee, Lease, Description [Line Items]
Initial term of operating leases			12 years
Maximum | Non-Aircraft
Lessee, Lease, Description [Line Items]
Initial term of operating leases			31 years
Forecast | Capacity Purchase Agreements
Lessee, Lease, Description [Line Items]
Scheduled block hours increase (decrease) percentage		10.00%
Change in cash obligation | $		$ 125