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Financial Instruments and Fair Value Measurements - Narrative (Details) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2021 USD ($) aircraft | Nov. 30, 2020 USD ($)
Fair Value [Line Items] |  |
Equity method investments | $ 160 |
Champlain |  |
Fair Value [Line Items] |  |
Number of aircraft operated | aircraft | 78 |
Republic |  |
Fair Value [Line Items] |  |
Number of aircraft operated | aircraft | 66 |
Corporate Debt | Maximum |  |
Fair Value [Line Items] |  |
Available-for-sale securities remaining maturities | 2 years |
Asset-Backed Securities | Minimum |  |
Fair Value [Line Items] |  |
Available-for-sale securities remaining maturities | 1 year |
Asset-Backed Securities | Maximum |  |
Fair Value [Line Items] |  |
Available-for-sale securities remaining maturities | 8 years |
U.S. Government and Agency Notes |  |
Fair Value [Line Items] |  |
Available-for-sale securities remaining maturities | 1 year |
Champlain |  |
Fair Value [Line Items] |  |
Equity method investment, ownership percentage | 40.00% |
Republic |  |
Fair Value [Line Items] |  |
Equity method investment, ownership percentage | 19.00% |
ManaAir |  |
Fair Value [Line Items] |  |
Equity method investment, ownership percentage | 49.90% |
Other Investment |  |
Fair Value [Line Items] |  |
Investment carrying value | $ 79 |
Kingsland | Standby Letters of Credit |  |
Fair Value [Line Items] |  |
Cash collateral for a standby letter of credit | $ 217 | $ 217
Avianca Holdings S.A. (“AVH”) | DIP Loan | United Airlines, Inc. |  |
Fair Value [Line Items] |  |
Interest rate | 14.50% |
Loan balance | $ 176 |
Boom Technology, Inc. |  |
Fair Value [Line Items] |  |
Notes receivable | 120 |
Notes receivable, carrying value | $ 44 |

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