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Available-for-Sale Debt Securities - Summary of the Balance Sheet Classification of Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
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Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale debt securities | $ 16,500 | $ 24,164
Cash and cash equivalents |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale debt securities | 2,291 | 10,592
Short-term marketable securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale debt securities | 12,721 | 12,149
Long-term marketable securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale debt securities | $ 1,488 | $ 1,423

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