Commitments and Contingencies - Narrative (Details) employee in Thousands, $ in Millions		1 Months Ended		9 Months Ended
	May 01, 2023 USD ($)	Sep. 30, 2023 USD ($) employee aircraft	Jan. 31, 2023 aircraft	Sep. 30, 2023 USD ($) employee aircraft	Sep. 29, 2023 aircraft	Sep. 28, 2023 aircraft	May 31, 2023 employee contract
Commitments and Contingencies [Line Items]
Lease term				12 years
Boeing 787-9 Aircraft
Commitments and Contingencies [Line Items]
Number of aircrafts to purchase						50
Boeing 787 Aircraft
Commitments and Contingencies [Line Items]
Additional purchase options granted						50
A321neo
Commitments and Contingencies [Line Items]
Number of aircraft expected to take delivery					60
Additional purchase rights granted					40
Number of mainline aircrafts		12		12
Embraer E175/E175LL
Commitments and Contingencies [Line Items]
Additional leases		47		47
International Association Of Machinists National Pension Plan
Commitments and Contingencies [Line Items]
Number of employees | employee							30
Number of contracts ratified | contract							5
Payment for ratification of contracts and taxes | $	$ 48
Air Line Pilots Association
Commitments and Contingencies [Line Items]
Pay rate increase period		4 years
Expenses associated with AIP | $				$ 765
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Number of employees | employee		102		102
Percentage of employees represented by various U.S. labor organizations				83.00%
Number of technicians			8,000
Bargaining on successor agreement, term			1 year
Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Aggregate principal amount of guarantee | $		$ 1,900		$ 1,900
Aircraft Mortgage Debt
Commitments and Contingencies [Line Items]
Aggregate principal amount of guarantee | $		81		81
Floating Rate Debt
Commitments and Contingencies [Line Items]
Long-term debt | $		11,400		$ 11,400
Remaining term of debt				12 years
Loans and Leases from Non-U.S. Entities
Commitments and Contingencies [Line Items]
Remaining term of debt				12 years
Aggregate balance | $		$ 8,200		$ 8,200