Available-for-sale investments (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	$ 17,171	$ 17,107
Gross unrealized gains	227	256
Gross unrealized losses	(54)	(38)
Estimated fair value	17,344	17,325
US Treasury securities [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	4,225	5,044
Gross unrealized gains	62	50
Gross unrealized losses	(2)	(14)
Estimated fair value	4,285	5,080
Other government related debt securities - Obligations of U.S. government agencies and FDIC guaranteed bank debt [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	1,634	2,158
Gross unrealized gains	27	51
Gross unrealized losses	(1)	(1)
Estimated fair value	1,660	2,208
Other government related debt securities - Foreign and other [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	476	837
Gross unrealized gains	15	16
Gross unrealized losses	0	(1)
Estimated fair value	491	852
Corporate debt securities - Financial [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	2,399	2,252
Gross unrealized gains	37	53
Gross unrealized losses	(12)	(9)
Estimated fair value	2,424	2,296
Corporate debt securities - Industrial [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	3,004	2,441
Gross unrealized gains	71	71
Gross unrealized losses	(25)	(5)
Estimated fair value	3,050	2,507
Corporate debt securities - Other [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	304	307
Gross unrealized gains	7	10
Gross unrealized losses	(2)	(1)
Estimated fair value	309	316
Mortgage and asset backed securities [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	1,565	841
Gross unrealized gains	8	5
Gross unrealized losses	(7)	(5)
Estimated fair value	1,566	841
Money market mutual funds [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	3,519	3,030
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Estimated fair value	3,519	3,030
Other short-term interest bearing securities [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost		147
Gross unrealized gains		0
Gross unrealized losses		0
Estimated fair value		147
Total debt security investments [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	17,126	17,057
Gross unrealized gains	227	256
Gross unrealized losses	(49)	(36)
Estimated fair value	17,304	17,277
Equity securities [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	45	50
Gross unrealized gains	0	0
Gross unrealized losses	(5)	(2)
Estimated fair value	$ 40	$ 48

- Definition

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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