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Debt - Narrative (Details) $ in Millions	3 Months Ended
Debt - Narrative (Details) $ in Millions	Jun. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)	Jun. 20, 2023 USD ($) aircraft
Debt Instrument [Line Items]
Unamortized debt discount		$ 303
Secured Debt \| Aircraft Purchase Financing Loans
Debt Instrument [Line Items]
Face amount			$ 1,300
Number of aircrafts delivered \| aircraft			39
Stated interest rate			5.80%
Secured Debt \| Term Loan Due 2021
Debt Instrument [Line Items]
Repayments of debt	$ 1,000
Revolving Credit Facility \| United Airlines, Inc. \| Secured Debt
Debt Instrument [Line Items]
Available under revolving credit facility		$ 1,750