Fair Value Measurement - Assets Measured at Fair Value (Details) - USD ($) $ in Millions | Mar. 31, 2019 | Dec. 31, 2018 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | $ 34,167 | $ 31,095 |
Total cash equivalents and marketable securities | 41,784 | 38,401 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Total cash equivalents and marketable securities | 32,095 | 29,105 |
Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Total cash equivalents and marketable securities | 9,689 | 9,296 |
Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Total cash equivalents and marketable securities | 0 | 0 |
U.S. government securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 16,794 | 13,836 |
U.S. government securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 16,794 | 13,836 |
U.S. government securities | Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 0 | 0 |
U.S. government securities | Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 0 | 0 |
U.S. government agency securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 8,039 | 8,333 |
U.S. government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 8,039 | 8,333 |
U.S. government agency securities | Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 0 | 0 |
U.S. government agency securities | Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 0 | 0 |
Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 9,334 | 8,926 |
Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 0 | 0 |
Corporate debt securities | Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 9,334 | 8,926 |
Corporate debt securities | Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Marketable securities | 0 | 0 |
Money market funds | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 6,969 | 6,792 |
Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 6,969 | 6,792 |
Money market funds | Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 0 | 0 |
Money market funds | Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 0 | 0 |
U.S. government securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 239 | 90 |
U.S. government securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 239 | 90 |
U.S. government securities | Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 0 | 0 |
U.S. government securities | Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 0 | 0 |
U.S. government agency securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 54 | 54 |
U.S. government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 54 | 54 |
U.S. government agency securities | Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 0 | 0 |
U.S. government agency securities | Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 0 | 0 |
Certificate of deposits and time deposits | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 355 | 369 |
Certificate of deposits and time deposits | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 0 | 0 |
Certificate of deposits and time deposits | Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | 355 | 369 |
Certificate of deposits and time deposits | Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | $ 0 | 0 |
Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | | 1 |
Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | | 0 |
Corporate debt securities | Significant Other Observable Inputs (Level 2) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | | 1 |
Corporate debt securities | Significant Unobservable Inputs (Level 3) | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis | | |
Cash equivalents | | $ 0 |