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Financial Instruments (Details 3) (USD $) | 3 Months Ended
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Mar. 31, 2014 | Mar. 31, 2013
Proceeds from Marketable Debt Securities |  |
Proceeds from maturities and sales | $ 757,512,000 | $ 4,329,506,000
Realized gains | 200,000 | 6,300,000
Realized losses | $ (100,000) | $ (2,000,000)

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