Investments In Marketable Securities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Gain Loss On Marketable Securities
Realized losses on the sale of available-for-sale securities	$ 0
Other-than-temporary impairment of marketable securities	0
Gains included in earnings that relate to trading securities held at the reporting date	1	0
Proceeds from sales of available-for-sale securities	1,704	1,523
Gross realized gains on sales	$ 0	$ 1

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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+ Details

- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of trading securities held at each balance sheet date, that was included in earnings for the period. Trading securities are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) and the change in net unrealized holding gain (loss) is included in earnings for the period.

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