Valuation of Debt and Equity Investments and Certain Liabilities - Investments at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 1,184	$ 1,199
Short-term investments	2,122	2,342
Long-term investments	228	224
Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	923	984
Short-term investments	2,122	2,342
Long-term investments	192	185
Estimate of Fair Value Measurement \| Available-for-sale securities \| Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	552	522
Short-term investments	0	0
Long-term investments	0	0
Estimate of Fair Value Measurement \| Available-for-sale securities \| Corporate obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	171	97
Short-term investments	375	390
Long-term investments	0	0
Estimate of Fair Value Measurement \| Available-for-sale securities \| U.S. Government agency and Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	200	365
Short-term investments	1,747	1,952
Long-term investments	0	0
Estimate of Fair Value Measurement \| 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	192	185
Portion at Other than Fair Value Measurement \| 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	26	27
Portion at Other than Fair Value Measurement \| Cost-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	10	12
Portion at Other than Fair Value Measurement \| Cash on hand
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	261	215
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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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No definition available.

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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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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph g

-Article 7

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