Valuation of Debt and Equity Investments and Certain Liabilities - Investments at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 1,502	$ 1,656
Short-term investments	3,611	2,813
Long-term investments	278	268
Measured at fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,352	1,397
Short-term investments	3,611	2,813
Long-term investments	253	236
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	475	525
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	378	172
Short-term investments	1,263	698
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	499	700
Short-term investments	2,348	2,115
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	253	236
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	21	26
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	6
Other measurement basis \| Cash on hand
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	150	259
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).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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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
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-Section S99
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