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Fair Value Measurements - Summary of assets and liabilities measured at fair value (Details) - USD ($) $ in Millions | Jun. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Assets: |  |
Available-for-sale debt securities | $ 22,561 | $ 29,587
Total | 7,854 | 5,465
Fair Value, Measurements, Recurring | Level 1 |  |
Assets: |  |
Total | 11,245 | 9,526
Liabilities: |  |
Total | 131 | 116
Fair Value, Measurements, Recurring | Level 1 | Corporate debt securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | U.S. treasury securities |  |
Assets: |  |
Available-for-sale debt securities | 3,391 | 4,061
Fair Value, Measurements, Recurring | Level 1 | Residential mortgage and asset-backed securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | U.S. government agencies securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | Certificates of deposit |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | Non-U.S. government securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | Money market funds |  |
Assets: |  |
Marketable equity securities | 7,060 | 4,714
Fair Value, Measurements, Recurring | Level 1 | Equity securities |  |
Assets: |  |
Marketable equity securities | 663 | 635
Fair Value, Measurements, Recurring | Level 1 | Deferred compensation plan |  |
Assets: |  |
Marketable equity securities | 131 | 116
Liabilities: |  |
Deferred compensation plan | 131 | 116
Fair Value, Measurements, Recurring | Level 1 | Foreign currency derivative contracts |  |
Assets: |  |
Foreign currency derivative contracts | 0 | 0
Liabilities: |  |
Foreign currency derivative contracts | 0 | 0
Fair Value, Measurements, Recurring | Level 2 |  |
Assets: |  |
Total | 19,223 | 25,539
Liabilities: |  |
Total | 11 | 93
Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities |  |
Assets: |  |
Available-for-sale debt securities | 12,092 | 14,747
Fair Value, Measurements, Recurring | Level 2 | U.S. treasury securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 2 | Residential mortgage and asset-backed securities |  |
Assets: |  |
Available-for-sale debt securities | 2,657 | 4,058
Fair Value, Measurements, Recurring | Level 2 | U.S. government agencies securities |  |
Assets: |  |
Available-for-sale debt securities | 872 | 926
Fair Value, Measurements, Recurring | Level 2 | Certificates of deposit |  |
Assets: |  |
Available-for-sale debt securities | 3,145 | 5,131
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. government securities |  |
Assets: |  |
Available-for-sale debt securities | 404 | 664
Fair Value, Measurements, Recurring | Level 2 | Money market funds |  |
Assets: |  |
Marketable equity securities | 0 | 0
Fair Value, Measurements, Recurring | Level 2 | Equity securities |  |
Assets: |  |
Marketable equity securities | 0 | 0
Fair Value, Measurements, Recurring | Level 2 | Deferred compensation plan |  |
Assets: |  |
Marketable equity securities | 0 | 0
Liabilities: |  |
Deferred compensation plan | 0 | 0
Fair Value, Measurements, Recurring | Level 2 | Foreign currency derivative contracts |  |
Assets: |  |
Foreign currency derivative contracts | 53 | 13
Liabilities: |  |
Foreign currency derivative contracts | 11 | 93
Fair Value, Measurements, Recurring | Level 3 |  |
Assets: |  |
Total | 0 | 0
Liabilities: |  |
Total | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Corporate debt securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | U.S. treasury securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Residential mortgage and asset-backed securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | U.S. government agencies securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Certificates of deposit |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Non-U.S. government securities |  |
Assets: |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Money market funds |  |
Assets: |  |
Marketable equity securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Equity securities |  |
Assets: |  |
Marketable equity securities | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Deferred compensation plan |  |
Assets: |  |
Marketable equity securities | 0 | 0
Liabilities: |  |
Deferred compensation plan | 0 | 0
Fair Value, Measurements, Recurring | Level 3 | Foreign currency derivative contracts |  |
Assets: |  |
Foreign currency derivative contracts | 0 | 0
Liabilities: |  |
Foreign currency derivative contracts | 0 | 0
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement |  |
Assets: |  |
Total | 30,468 | 35,065
Liabilities: |  |
Total | 142 | 209
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Corporate debt securities |  |
Assets: |  |
Available-for-sale debt securities | 12,092 | 14,747
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | U.S. treasury securities |  |
Assets: |  |
Available-for-sale debt securities | 3,391 | 4,061
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Residential mortgage and asset-backed securities |  |
Assets: |  |
Available-for-sale debt securities | 2,657 | 4,058
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | U.S. government agencies securities |  |
Assets: |  |
Available-for-sale debt securities | 872 | 926
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Certificates of deposit |  |
Assets: |  |
Available-for-sale debt securities | 3,145 | 5,131
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Non-U.S. government securities |  |
Assets: |  |
Available-for-sale debt securities | 404 | 664
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Money market funds |  |
Assets: |  |
Marketable equity securities | 7,060 | 4,714
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Equity securities |  |
Assets: |  |
Marketable equity securities | 663 | 635
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Deferred compensation plan |  |
Assets: |  |
Marketable equity securities | 131 | 116
Liabilities: |  |
Deferred compensation plan | 131 | 116
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Foreign currency derivative contracts |  |
Assets: |  |
Foreign currency derivative contracts | 53 | 13
Liabilities: |  |
Foreign currency derivative contracts | $ 11 | $ 93

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