Valuation of Debt and Equity Investments and Certain Liabilities - Investments at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 3,720	$ 2,438
Short-term investments	366	1,795
Long-term investments	281	251
Measured at fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,435	2,208
Short-term investments	366	1,795
Long-term investments	250	226
Measured at fair value \| Available-for-sale debt securities \| Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,073	747
Short-term investments	0	0
Long-term investments	0	0
Measured at fair value \| Available-for-sale debt securities \| Corporate obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	865	473
Short-term investments	266	748
Long-term investments	0	0
Measured at fair value \| Available-for-sale debt securities \| U.S. government agency and Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,497	988
Short-term investments	100	1,047
Long-term investments	0	0
Measured at fair value \| Trading securities \| Mutual funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Short-term investments	0	0
Long-term investments	250	226
Other measurement basis \| Equity-method investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Short-term investments	0	0
Long-term investments	27	21
Other measurement basis \| Non-marketable equity investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Short-term investments	0	0
Long-term investments	4	4
Other measurement basis \| Cash on hand
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	285	230
Short-term investments	0	0
Long-term investments	$ 0	$ 0

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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- Definition

Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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