Fair value measurements Summary of Classification on Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities
Total	$ 6,310	$ 5,465
Cash and cash equivalents
Fair Value, Assets and Liabilities
Marketable equity securities	5,305	4,714
Prepaid Expenses and Other Current Assets [Member]
Fair Value, Assets and Liabilities
Marketable equity securities	863	637
Other long-term assets
Fair Value, Assets and Liabilities
Marketable equity securities	$ 142	$ 114

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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+ References

No definition available.

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