Fair Value Measurements - Summary of assets and liabilities recorded at fair value (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets
Available-for-sale debt securities	$ 2,026	$ 16,500
Total	6,970	11,039
Fair value, recurring \| Fair value
Assets
Total	9,008	27,576
Liabilities
Total	339	179
Fair value, recurring \| Fair value \| U.S. treasury securities
Assets
Available-for-sale debt securities	309	2,433
Fair value, recurring \| Fair value \| Certificates of deposit
Assets
Available-for-sale debt securities	216	3,517
Fair value, recurring \| Fair value \| U.S. government agencies securities
Assets
Available-for-sale debt securities	0	1,081
Fair value, recurring \| Fair value \| Non-U.S. government securities
Assets
Available-for-sale debt securities	43	174
Fair value, recurring \| Fair value \| Corporate debt securities
Assets
Available-for-sale debt securities	1,142	9,204
Fair value, recurring \| Fair value \| Residential mortgage and asset-backed securities
Assets
Available-for-sale debt securities	316	91
Fair value, recurring \| Fair value \| Equity investment in Galapagos
Assets
Marketable equity securities	1,648	3,477
Fair value, recurring \| Fair value \| Money market funds
Assets
Marketable equity securities	4,361	7,069
Fair value, recurring \| Fair value \| Other publicly traded equity securities
Assets
Marketable equity securities	743	322
Fair value, recurring \| Fair value \| Deferred compensation plan
Assets
Marketable equity securities	218	171
Liabilities
Deferred compensation plan	218	171
Fair value, recurring \| Fair value \| Foreign currency derivative contracts
Assets
Foreign currency derivative contracts	12	37
Liabilities
Foreign currency derivative contracts	121	8
Fair value, recurring \| Level 1
Assets
Total	7,279	13,472
Liabilities
Total	218	171
Fair value, recurring \| Level 1 \| U.S. treasury securities
Assets
Available-for-sale debt securities	309	2,433
Fair value, recurring \| Level 1 \| Certificates of deposit
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 1 \| U.S. government agencies securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 1 \| Non-U.S. government securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 1 \| Corporate debt securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 1 \| Residential mortgage and asset-backed securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 1 \| Equity investment in Galapagos
Assets
Marketable equity securities	1,648	3,477
Fair value, recurring \| Level 1 \| Money market funds
Assets
Marketable equity securities	4,361	7,069
Fair value, recurring \| Level 1 \| Other publicly traded equity securities
Assets
Marketable equity securities	743	322
Fair value, recurring \| Level 1 \| Deferred compensation plan
Assets
Marketable equity securities	218	171
Liabilities
Deferred compensation plan	218	171
Fair value, recurring \| Level 1 \| Foreign currency derivative contracts
Assets
Foreign currency derivative contracts	0	0
Liabilities
Foreign currency derivative contracts	0	0
Fair value, recurring \| Level 2
Assets
Total	1,729	14,104
Liabilities
Total	121	8
Fair value, recurring \| Level 2 \| U.S. treasury securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 2 \| Certificates of deposit
Assets
Available-for-sale debt securities	216	3,517
Fair value, recurring \| Level 2 \| U.S. government agencies securities
Assets
Available-for-sale debt securities	0	1,081
Fair value, recurring \| Level 2 \| Non-U.S. government securities
Assets
Available-for-sale debt securities	43	174
Fair value, recurring \| Level 2 \| Corporate debt securities
Assets
Available-for-sale debt securities	1,142	9,204
Fair value, recurring \| Level 2 \| Residential mortgage and asset-backed securities
Assets
Available-for-sale debt securities	316	91
Fair value, recurring \| Level 2 \| Equity investment in Galapagos
Assets
Marketable equity securities	0	0
Fair value, recurring \| Level 2 \| Money market funds
Assets
Marketable equity securities	0	0
Fair value, recurring \| Level 2 \| Other publicly traded equity securities
Assets
Marketable equity securities	0	0
Fair value, recurring \| Level 2 \| Deferred compensation plan
Assets
Marketable equity securities	0	0
Liabilities
Deferred compensation plan	0	0
Fair value, recurring \| Level 2 \| Foreign currency derivative contracts
Assets
Foreign currency derivative contracts	12	37
Liabilities
Foreign currency derivative contracts	121	8
Fair value, recurring \| Level 3
Assets
Total	0	0
Liabilities
Total	0	0
Fair value, recurring \| Level 3 \| U.S. treasury securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 3 \| Certificates of deposit
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 3 \| U.S. government agencies securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 3 \| Non-U.S. government securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 3 \| Corporate debt securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 3 \| Residential mortgage and asset-backed securities
Assets
Available-for-sale debt securities	0	0
Fair value, recurring \| Level 3 \| Equity investment in Galapagos
Assets
Marketable equity securities	0	0
Fair value, recurring \| Level 3 \| Money market funds
Assets
Marketable equity securities	0	0
Fair value, recurring \| Level 3 \| Other publicly traded equity securities
Assets
Marketable equity securities	0	0
Fair value, recurring \| Level 3 \| Deferred compensation plan
Assets
Marketable equity securities	0	0
Liabilities
Deferred compensation plan	0	0
Fair value, recurring \| Level 3 \| Foreign currency derivative contracts
Assets
Foreign currency derivative contracts	0	0
Liabilities
Foreign currency derivative contracts	$ 0	$ 0

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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