Fair value measurements Summary of assets and liabilities recorded at fair value (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Assets
Available-for-sale debt securities	$ 24,164	$ 29,587
Total	6,310	5,465
Fair Value, Measurements, Recurring \| Fair value
Assets
Total	30,552	35,065
Liabilities
Total	125	209
Fair Value, Measurements, Recurring \| Fair value \| U.S. treasury securities
Assets
Available-for-sale debt securities	3,969	4,061
Fair Value, Measurements, Recurring \| Fair value \| Certificates of deposit
Assets
Available-for-sale debt securities	4,361	5,131
Fair Value, Measurements, Recurring \| Fair value \| U.S. government agencies securities
Assets
Available-for-sale debt securities	938	926
Fair Value, Measurements, Recurring \| Fair value \| Non-U.S. government securities
Assets
Available-for-sale debt securities	305	664
Fair Value, Measurements, Recurring \| Fair value \| Corporate debt securities
Assets
Available-for-sale debt securities	13,067	14,747
Fair Value, Measurements, Recurring \| Fair value \| Residential mortgage and asset-backed securities
Assets
Available-for-sale debt securities	1,524	4,058
Fair Value, Measurements, Recurring \| Fair value \| Money market funds
Assets
Marketable equity securities	5,305	4,714
Fair Value, Measurements, Recurring \| Fair value \| Equity securities
Assets
Marketable equity securities	881	635
Fair Value, Measurements, Recurring \| Fair value \| Deferred compensation plan
Assets
Marketable equity securities	124	116
Liabilities
Deferred compensation plan	124	116
Fair Value, Measurements, Recurring \| Fair value \| Foreign currency derivative contracts
Assets
Foreign currency derivative contracts	78	13
Liabilities
Foreign currency derivative contracts	1	93
Fair Value, Measurements, Recurring \| Level 1
Assets
Total	10,279	9,526
Liabilities
Total	124	116
Fair Value, Measurements, Recurring \| Level 1 \| U.S. treasury securities
Assets
Available-for-sale debt securities	3,969	4,061
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 \| Money market funds
Assets
Marketable equity securities	5,305	4,714
Fair Value, Measurements, Recurring \| Level 1 \| Equity securities
Assets
Marketable equity securities	881	635
Fair Value, Measurements, Recurring \| Level 1 \| Deferred compensation plan
Assets
Marketable equity securities	124	116
Liabilities
Deferred compensation plan	124	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	20,273	25,539
Liabilities
Total	1	93
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	4,361	5,131
Fair Value, Measurements, Recurring \| Level 2 \| U.S. government agencies securities
Assets
Available-for-sale debt securities	938	926
Fair Value, Measurements, Recurring \| Level 2 \| Non-U.S. government securities
Assets
Available-for-sale debt securities	305	664
Fair Value, Measurements, Recurring \| Level 2 \| Corporate debt securities
Assets
Available-for-sale debt securities	13,067	14,747
Fair Value, Measurements, Recurring \| Level 2 \| Residential mortgage and asset-backed securities
Assets
Available-for-sale debt securities	1,524	4,058
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	78	13
Liabilities
Foreign currency derivative contracts	1	93
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 \| 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

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