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Years remaining on debt instruments.

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Loans Receivable, Aggregate Maximum Payment And Guarantee Amount

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Loans Receivable, Agreement, Put Option, Deposit Receipts

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Loans Receivable, Guarantee And Payout Share Price At Fifth Anniversary

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Number Of Aircrafts Expected To Take Delivery, New Purchases, Year Three

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Number Of Aircrafts Expected To Take Delivery, Rescheduled Deliveries, Year Three

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Number Of Aircrafts Expected To Take Delivery, Rescheduled Deliveries, Year Two

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Number of Call Options To Purchase Regional Jet Aircraft

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Percentage of employees represented by labor organizations

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Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

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Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

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Face (par) amount of debt instrument at time of issuance.

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The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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Commitments and Contingencies - Narrative (Details)	12 Months Ended
Commitments and Contingencies - Narrative (Details)	Dec. 31, 2020 USD ($) aircraftCommitment employee option $ / shares shares	Feb. 26, 2021 aircraft	Nov. 30, 2020 USD ($)
Commitments and Contingencies [Line Items]
Cash collateral for a standby letter of credit	$ 217,000,000
Aggregate balance	$ 11,100,000,000
Number of call options to purchase regional jet aircraft \| option	303
United Airlines, Inc.
Commitments and Contingencies [Line Items]
Number of employees \| employee	74,400
Percentage of employees represented by various U.S. labor organizations	84.00%
United Airlines, Inc. \| Surety Bonds
Commitments and Contingencies [Line Items]
Long-term line of credit	$ 380,000,000
Tax-Exempt Special Facilities Revenue Bonds
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	1,900,000,000
Tax-Exempt Special Facilities Revenue Bonds \| Indirect Guarantee of Indebtedness
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	293,000,000
Contingent liabilities based on participation	2,300,000,000
Aircraft Mortgage Debt
Commitments and Contingencies [Line Items]
Guarantor obligations, maximum exposure	119,000,000
Floating Rate Debt
Commitments and Contingencies [Line Items]
Aggregate principal amount	$ 9,800,000,000
Debt instrument, remaining terms	12 years
Loans And Leases From Non U S Entities
Commitments and Contingencies [Line Items]
Debt instrument, remaining terms	12 years
Aggregate balance	$ 8,300,000,000
Kingsland
Commitments and Contingencies [Line Items]
Number of shares that may be put to United (in shares) \| shares	144,800,000
Number of ADRs that may be put to United (in shares) \| shares	18,100,000
Market price of common stock at fifth anniversary (in dollars per share) \| $ / shares	$ 12
Aggregate maximum possible combined put payment and guarantee amount	$ 217,000,000
Kingsland \| Standby Letter of Credit
Commitments and Contingencies [Line Items]
Cash collateral for a standby letter of credit			$ 217,000,000
Boeing 737-700
Commitments and Contingencies [Line Items]
Number of firm commitments \| aircraftCommitment	11
Airbus A319
Commitments and Contingencies [Line Items]
Number of firm commitments \| aircraftCommitment	17
Boeing 737 MAX
Commitments and Contingencies [Line Items]
Number of firm commitments \| aircraftCommitment	188
Boeing 737 MAX \| Subsequent Event
Commitments and Contingencies [Line Items]
Scheduled aircraft deliveries for 2023 from new firm orders \| aircraft		25
Scheduled aircraft deliveries for 2022 from rescheduled deliveries \| aircraft		40
Scheduled aircraft deliveries for 2023 from rescheduled deliveries \| aircraft		5