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Financial Instruments and Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Nov. 30, 2020
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 | 9 years |  |
Corporate Debt | Maximum |  |  |
Fair Value [Line Items] |  |  |
Available-for-sale securities remaining maturities | 2 years |  |
U.S. Government and Agency Notes |  |  |
Fair Value [Line Items] |  |  |
Available-for-sale securities remaining maturities | 1 year |  |
Azul |  |  |
Fair Value [Line Items] |  |  |
Equity stake in Azul | 2.00% |  |
Gain (loss) on equity securities | $ (23) | $ 293 |
Carrying value of investment | $ 182 |  |
Azul | Preferred Stock |  |  |
Fair Value [Line Items] |  |  |
Equity stake in Azul | 8.00% |  |
Kingsland | Standby Letters of Credit |  |  |
Fair Value [Line Items] |  |  |
Cash collateral for a standby letter of credit |  |  | $ 217
Avianca Holdings S.A. (“AVH”) | DIP Loan | United Airlines, Inc. |  |  |
Fair Value [Line Items] |  |  |
Interest rate | 14.50% |  |
Loan balance | $ 164 |  |

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