Marketable Securities And Cash Equivalents (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cost of marketable securities and cash equivalents	$ 1,741	$ 2,340
Unrealized gains on marketable securities and cash equivalents		3
Unrealized losses on marketable securities and cash equivalents	(38)	(5)
Fair value of marketable securities and cash equivalents	1,703	2,338
United States Government Obligations [Member] \| Maturity Less Than 1 Year [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	375	583
Fair Value	375	583
United States Government Obligations [Member] \| Maturity 1 To 5 Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	90	93
Fair Value	90	93
Government-Sponsored Enterprise Obligations [Member] \| Maturity 1 To 5 Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3	2
Fair Value	3	2
Corporate Debt Securities [Member] \| Maturity 1 To 5 Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	14	15
Fair Value	14	15
Other Debt Instruments [Member] \| Maturity Less Than 1 Year [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	645	1,038
Fair Value	645	1,038
Other Debt Instruments [Member] \| Maturity 1 To 5 Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3	3
Fair Value	3	3
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	611	606
Unrealized gains on available for sale securities		3
Unrealized losses on available for sale securities	(38)	(5)
Fair Value	$ 573	$ 604

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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