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Financial Instruments and Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2019 | Nov. 30, 2018 | Apr. 30, 2018
Synergy |  |  |
Fair Value [Line Items] |  |  |
Loan amount |  | $ 456 |
Number of shares pledged as loan collateral (in shares) |  | 516,000,000 |
Azul |  |  |
Fair Value [Line Items] |  |  |
Equity stake |  |  | 2.00%
Azul | Preferred Stock |  |  |
Fair Value [Line Items] |  |  |
Equity stake |  |  | 8.00%
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 | 16 years |  |
Corporate Debt | Minimum |  |  |
Fair Value [Line Items] |  |  |
Available-for-sale securities remaining maturities | 1 year |  |
Corporate Debt | Maximum |  |  |
Fair Value [Line Items] |  |  |
Available-for-sale securities remaining maturities | 3 years |  |
CDARS | Maximum |  |  |
Fair Value [Line Items] |  |  |
Available-for-sale securities remaining maturities | 1 year |  |
U.S. Government and Other Securities | Minimum |  |  |
Fair Value [Line Items] |  |  |
Available-for-sale securities remaining maturities | 1 year |  |
Other Fixed-Income Securities | Maximum |  |  |
Fair Value [Line Items] |  |  |
Available-for-sale securities remaining maturities | 2 years |  |

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