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Financial Instruments and Fair Value Measurements - Narrative (Details) - USD ($) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Fair Value [Line Items] |  |  |  |
Gain (loss) on equity securities |  | $ 25,000,000 |  | $ 77,000,000
Unrealized gain (loss) on derivative asset |  | (4,000,000) | $ (24,000,000) | (5,000,000)
MileagePlus Financing | Secured Debt |  |  |  |
Fair Value [Line Items] |  |  |  |
Face amount | $ 6,800,000,000 |  | $ 6,800,000,000 |
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 |  |  | 14 years |
Corporate Debt | Maximum |  |  |  |
Fair Value [Line Items] |  |  |  |
Available-for-sale securities remaining maturities |  |  | 3 years |
U.S. Government and Agency Notes |  |  |  |
Fair Value [Line Items] |  |  |  |
Available-for-sale securities remaining maturities |  |  | 2 years |
Other Fixed-Income Securities |  |  |  |
Fair Value [Line Items] |  |  |  |
Available-for-sale securities remaining maturities |  |  | 1 year |
Azul |  |  |  |
Fair Value [Line Items] |  |  |  |
Equity stake in Azul | 2.00% |  | 2.00% |
Gain (loss) on equity securities | $ 17,000,000 | $ 21,000,000 | $ 267,000,000 | $ 73,000,000
Carrying value of investment | $ 118,000,000 |  | $ 118,000,000 |
Azul | Preferred Stock |  |  |  |
Fair Value [Line Items] |  |  |  |
Equity stake in Azul | 8.00% |  | 8.00% |

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