Commitments and Contingencies - Narrative (Details) $ / shares in Units, shares in Millions	1 Months Ended		3 Months Ended	9 Months Ended
	Oct. 20, 2021 supplier kitchen	Sep. 30, 2021 USD ($) commitment aircraft employee	Sep. 30, 2021 USD ($) commitment aircraft employee	Sep. 30, 2021 USD ($) commitment aircraft employee	Dec. 31, 2021 USD ($)	Aug. 31, 2021 USD ($)	Nov. 30, 2020 USD ($)	Nov. 30, 2018 USD ($) $ / shares shares
Commitments and Contingencies [Line Items]
Number of aircraft delivered | aircraft				20
Remaining term of debt				11 years
Subsequent Event
Commitments and Contingencies [Line Items]
Percentage of employees represented by various U.S. labor organizations	70.00%
Number of outside suppliers | supplier	3
Number of kitchens | kitchen	5
Flight Equipment
Commitments and Contingencies [Line Items]
Number of aircraft delivered | aircraft				7
Operating Lease Right-of-Use Assets
Commitments and Contingencies [Line Items]
Number of aircraft delivered | aircraft				13
Current/Long-Term Obligations under Operating Leases
Commitments and Contingencies [Line Items]
Number of aircraft delivered | aircraft				13
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Number of employees | employee		85,300	85,300	85,300
Percentage of employees represented by various U.S. labor organizations				85.00%
Avianca Holdings S.A. (“AVH”) | Forecast
Commitments and Contingencies [Line Items]
Common stock, value outstanding					$ 0
BRW | Term Loan Receivable
Commitments and Contingencies [Line Items]
Loan amount								$ 456,000,000
Kingsland
Commitments and Contingencies [Line Items]
Number of shares that may be put to United (in shares) | shares								144.8
Number of ADRs that may be put into United (in shares) | shares								18.1
Market price of common stock at fifth anniversary (in dollars per share) (less than) | $ / shares								$ 12
Aggregate maximum possible combined put payment and guarantee amount								$ 217,000,000
Kingsland | Standby Letters of Credit
Commitments and Contingencies [Line Items]
Cash collateral for a standby letter of credit		$ 217,000,000	$ 217,000,000	$ 217,000,000			$ 217,000,000
Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Aggregate principal amount of guarantee		2,100,000,000	2,100,000,000	2,100,000,000
Aircraft Mortgage Debt
Commitments and Contingencies [Line Items]
Aggregate principal amount of guarantee		109,000,000	109,000,000	109,000,000
Floating Rate Debt
Commitments and Contingencies [Line Items]
Debt		13,300,000,000	13,300,000,000	$ 13,300,000,000
Loans and Leases from Non-U.S. Entities
Commitments and Contingencies [Line Items]
Remaining term of debt				11 years
Aggregate balance		$ 10,100,000,000	$ 10,100,000,000	$ 10,100,000,000
Special Facility Revenue Bonds | Secured Debt
Commitments and Contingencies [Line Items]
Face amount						$ 289,000,000
Stated interest rate						4.00%
Boeing 737 MAX
Commitments and Contingencies [Line Items]
Number of aircraft delivered | aircraft			8
Number of aircraft committed to purchase | commitment		371	371	371
Airbus A321neo
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | commitment		70	70	70
Airbus A319
Commitments and Contingencies [Line Items]
Number of aircraft committed to purchase | aircraft		10	10	10
Embraer E175
Commitments and Contingencies [Line Items]
Number of aircraft operated | aircraft		38
Embraer E175 | United Airlines, Inc.
Commitments and Contingencies [Line Items]
Long-term purchase commitment, period		12 years