Available-for-sale investments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	$ 23,455	$ 19,814
Gross unrealized gains	312	224
Gross unrealized losses	(22)	(35)
Total available-for-sale investments, fair value	23,745	20,003
U.S. 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	4,443	3,878
Gross unrealized gains	15	68
Gross unrealized losses	0	0
Total available-for-sale investments, fair value	4,458	3,946
Other government-related debt securities - U.S. [Member]
Amortized cost, gross unrealized gains, gross unrealized losses and estimated fair values of available-for-sale investments by type of security
Amortized cost	1,018	1,548
Gross unrealized gains	12	23
Gross unrealized losses	0	0
Total available-for-sale investments, fair value	1,030	1,571
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	1,549	441
Gross unrealized gains	60	9
Gross unrealized losses	(1)	0
Total available-for-sale investments, fair value	1,608	450
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	3,266	2,493
Gross unrealized gains	96	30
Gross unrealized losses	(1)	(15)
Total available-for-sale investments, fair value	3,361	2,508
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	4,283	3,077
Gross unrealized gains	100	79
Gross unrealized losses	(3)	(10)
Total available-for-sale investments, fair value	4,380	3,146
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	441	280
Gross unrealized gains	11	9
Gross unrealized losses	0	0
Total available-for-sale investments, fair value	452	289
Residential mortgage-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	1,828	518
Gross unrealized gains	9	3
Gross unrealized losses	(8)	(3)
Total available-for-sale investments, fair value	1,829	518
Other 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	1,769	1,271
Gross unrealized gains	7	3
Gross unrealized losses	(9)	(7)
Total available-for-sale investments, fair value	1,767	1,267
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	2,620	6,266
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Total available-for-sale investments, fair value	2,620	6,266
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	2,186
Gross unrealized gains	0
Gross unrealized losses	0
Total available-for-sale investments, fair value	2,186
Total 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	23,403	19,772
Gross unrealized gains	310	224
Gross unrealized losses	(22)	(35)
Total available-for-sale investments, fair value	23,691	19,961
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	52	42
Gross unrealized gains	2	0
Gross unrealized losses	0	0
Total available-for-sale investments, fair value	$ 54	$ 42

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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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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- Definition

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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