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Fair value measurements Summary of assets and liabilities recorded at fair value (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Assets |  |
Available-for-sale debt securities | $ 16,500 | $ 24,164
Total | 7,562 | 5,688
Equity investment in Galapagos |  |
Assets |  |
Total | 3,477 | 622
Fair Value, Recurring [Member] | Fair value |  |
Assets |  |
Total | 27,576 | 30,552
Liabilities |  |
Total | 179 | 125
Fair Value, Recurring [Member] | Fair value | U.S. treasury securities |  |
Assets |  |
Available-for-sale debt securities | 2,433 | 3,969
Fair Value, Recurring [Member] | Fair value | Certificates of deposit |  |
Assets |  |
Available-for-sale debt securities | 3,517 | 4,361
Fair Value, Recurring [Member] | Fair value | U.S. government agencies securities |  |
Assets |  |
Available-for-sale debt securities | 1,081 | 938
Fair Value, Recurring [Member] | Fair value | Non-U.S. government securities |  |
Assets |  |
Available-for-sale debt securities | 174 | 305
Fair Value, Recurring [Member] | Fair value | Corporate debt securities |  |
Assets |  |
Available-for-sale debt securities | 9,204 | 13,067
Fair Value, Recurring [Member] | Fair value | Residential mortgage and asset-backed securities |  |
Assets |  |
Available-for-sale debt securities | 91 | 1,524
Fair Value, Recurring [Member] | Fair value | Equity investment in Galapagos |  |
Assets |  |
Marketable equity securities | 3,477 | 622
Fair Value, Recurring [Member] | Fair value | Money market funds |  |
Assets |  |
Marketable equity securities | 7,069 | 5,305
Fair Value, Recurring [Member] | Fair value | Other publicly traded equity securities |  |
Assets |  |
Marketable equity securities | 322 | 259
Fair Value, Recurring [Member] | Fair value | Deferred compensation plan |  |
Assets |  |
Marketable equity securities | 171 | 124
Liabilities |  |
Deferred compensation plan | 171 | 124
Fair Value, Recurring [Member] | Fair value | Foreign currency derivative contracts |  |
Assets |  |
Foreign currency derivative contracts | 37 | 78
Liabilities |  |
Foreign currency derivative contracts | 8 | 1
Fair Value, Recurring [Member] | Level 1 |  |
Assets |  |
Total | 13,472 | 10,279
Liabilities |  |
Total | 171 | 124
Fair Value, Recurring [Member] | Level 1 | U.S. treasury securities |  |
Assets |  |
Available-for-sale debt securities | 2,433 | 3,969
Fair Value, Recurring [Member] | Level 1 | Certificates of deposit |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 1 | U.S. government agencies securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 1 | Non-U.S. government securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 1 | Corporate debt securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 1 | Residential mortgage and asset-backed securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 1 | Equity investment in Galapagos |  |
Assets |  |
Marketable equity securities | 3,477 | 622
Fair Value, Recurring [Member] | Level 1 | Money market funds |  |
Assets |  |
Marketable equity securities | 7,069 | 5,305
Fair Value, Recurring [Member] | Level 1 | Other publicly traded equity securities |  |
Assets |  |
Marketable equity securities | 322 | 259
Fair Value, Recurring [Member] | Level 1 | Deferred compensation plan |  |
Assets |  |
Marketable equity securities | 171 | 124
Liabilities |  |
Deferred compensation plan | 171 | 124
Fair Value, Recurring [Member] | Level 1 | Foreign currency derivative contracts |  |
Assets |  |
Foreign currency derivative contracts | 0 | 0
Liabilities |  |
Foreign currency derivative contracts | 0 | 0
Fair Value, Recurring [Member] | Level 2 |  |
Assets |  |
Total | 14,104 | 20,273
Liabilities |  |
Total | 8 | 1
Fair Value, Recurring [Member] | Level 2 | U.S. treasury securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 2 | Certificates of deposit |  |
Assets |  |
Available-for-sale debt securities | 3,517 | 4,361
Fair Value, Recurring [Member] | Level 2 | U.S. government agencies securities |  |
Assets |  |
Available-for-sale debt securities | 1,081 | 938
Fair Value, Recurring [Member] | Level 2 | Non-U.S. government securities |  |
Assets |  |
Available-for-sale debt securities | 174 | 305
Fair Value, Recurring [Member] | Level 2 | Corporate debt securities |  |
Assets |  |
Available-for-sale debt securities | 9,204 | 13,067
Fair Value, Recurring [Member] | Level 2 | Residential mortgage and asset-backed securities |  |
Assets |  |
Available-for-sale debt securities | 91 | 1,524
Fair Value, Recurring [Member] | Level 2 | Equity investment in Galapagos |  |
Assets |  |
Marketable equity securities | 0 | 0
Fair Value, Recurring [Member] | Level 2 | Money market funds |  |
Assets |  |
Marketable equity securities | 0 | 0
Fair Value, Recurring [Member] | Level 2 | Other publicly traded equity securities |  |
Assets |  |
Marketable equity securities | 0 | 0
Fair Value, Recurring [Member] | Level 2 | Deferred compensation plan |  |
Assets |  |
Marketable equity securities | 0 | 0
Liabilities |  |
Deferred compensation plan | 0 | 0
Fair Value, Recurring [Member] | Level 2 | Foreign currency derivative contracts |  |
Assets |  |
Foreign currency derivative contracts | 37 | 78
Liabilities |  |
Foreign currency derivative contracts | 8 | 1
Fair Value, Recurring [Member] | Level 3 |  |
Assets |  |
Total | 0 | 0
Liabilities |  |
Total | 0 | 0
Fair Value, Recurring [Member] | Level 3 | U.S. treasury securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 3 | Certificates of deposit |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 3 | U.S. government agencies securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 3 | Non-U.S. government securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 3 | Corporate debt securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 3 | Residential mortgage and asset-backed securities |  |
Assets |  |
Available-for-sale debt securities | 0 | 0
Fair Value, Recurring [Member] | Level 3 | Equity investment in Galapagos |  |
Assets |  |
Marketable equity securities | 0 | 0
Fair Value, Recurring [Member] | Level 3 | Money market funds |  |
Assets |  |
Marketable equity securities | 0 | 0
Fair Value, Recurring [Member] | Level 3 | Other publicly traded equity securities |  |
Assets |  |
Marketable equity securities | 0 | 0
Fair Value, Recurring [Member] | Level 3 | Deferred compensation plan |  |
Assets |  |
Marketable equity securities | 0 | 0
Liabilities |  |
Deferred compensation plan | 0 | 0
Fair Value, Recurring [Member] | Level 3 | Foreign currency derivative contracts |  |
Assets |  |
Foreign currency derivative contracts | 0 | 0
Liabilities |  |
Foreign currency derivative contracts | $ 0 | $ 0

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