Fair Value Measurements Summary of Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets:
Available-for-sale debt securities	$ 13,399	$ 16,500
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement
Assets:
Total	28,015	27,576
Liabilities:
Total	250	179
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | U.S. treasury securities
Assets:
Available-for-sale debt securities	2,238	2,433
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Certificates of deposit
Assets:
Available-for-sale debt securities	2,136	3,517
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | U.S. government agencies securities
Assets:
Available-for-sale debt securities	71	1,081
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Non-U.S. government securities
Assets:
Available-for-sale debt securities	220	174
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Corporate debt securities
Assets:
Available-for-sale debt securities	7,525	9,204
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Residential mortgage and asset-backed securities
Assets:
Available-for-sale debt securities	1,209	91
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Equity investment in Galapagos
Assets:
Marketable equity securities	2,361	3,477
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Money market funds
Assets:
Marketable equity securities	11,430	7,069
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Other publicly traded equity securities
Assets:
Marketable equity securities	619	322
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Deferred compensation plan
Assets:
Marketable equity securities	200	171
Liabilities:
Deferred compensation plan	200	171
Fair Value, Measurements, Recurring | Estimate of Fair Value Measurement | Foreign currency derivative contracts
Assets:
Foreign currency derivative contracts	6	37
Liabilities:
Foreign currency derivative contracts	50	8
Fair Value, Measurements, Recurring | Level 1
Assets:
Total	16,848	13,472
Liabilities:
Total	200	171
Fair Value, Measurements, Recurring | Level 1 | U.S. treasury securities
Assets:
Available-for-sale debt securities	2,238	2,433
Fair Value, Measurements, Recurring | Level 1 | Certificates of deposit
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 | Non-U.S. government securities
Assets:
Available-for-sale debt securities	0	0
Fair Value, Measurements, Recurring | Level 1 | Corporate debt securities
Assets:
Available-for-sale debt securities	0	0
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 | Equity investment in Galapagos
Assets:
Marketable equity securities	2,361	3,477
Fair Value, Measurements, Recurring | Level 1 | Money market funds
Assets:
Marketable equity securities	11,430	7,069
Fair Value, Measurements, Recurring | Level 1 | Other publicly traded equity securities
Assets:
Marketable equity securities	619	322
Fair Value, Measurements, Recurring | Level 1 | Deferred compensation plan
Assets:
Marketable equity securities	200	171
Liabilities:
Deferred compensation plan	200	171
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	11,167	14,104
Liabilities:
Total	50	8
Fair Value, Measurements, Recurring | Level 2 | U.S. treasury securities
Assets:
Available-for-sale debt securities	0	0
Fair Value, Measurements, Recurring | Level 2 | Certificates of deposit
Assets:
Available-for-sale debt securities	2,136	3,517
Fair Value, Measurements, Recurring | Level 2 | U.S. government agencies securities
Assets:
Available-for-sale debt securities	71	1,081
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. government securities
Assets:
Available-for-sale debt securities	220	174
Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities
Assets:
Available-for-sale debt securities	7,525	9,204
Fair Value, Measurements, Recurring | Level 2 | Residential mortgage and asset-backed securities
Assets:
Available-for-sale debt securities	1,209	91
Fair Value, Measurements, Recurring | Level 2 | Equity investment in Galapagos
Assets:
Marketable equity securities	0	0
Fair Value, Measurements, Recurring | Level 2 | Money market funds
Assets:
Marketable equity securities	0	0
Fair Value, Measurements, Recurring | Level 2 | Other publicly traded 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	6	37
Liabilities:
Foreign currency derivative contracts	50	8
Fair Value, Measurements, Recurring | Level 3
Assets:
Total	0	0
Liabilities:
Total	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 | Certificates of deposit
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 | Non-U.S. government securities
Assets:
Available-for-sale debt securities	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 | Residential mortgage and asset-backed securities
Assets:
Available-for-sale debt securities	0	0
Fair Value, Measurements, Recurring | Level 3 | Equity investment in Galapagos
Assets:
Marketable equity securities	0	0
Fair Value, Measurements, Recurring | Level 3 | Money market funds
Assets:
Marketable equity securities	0	0
Fair Value, Measurements, Recurring | Level 3 | Other publicly traded 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