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Financial Instruments (Details 3) (USD $) | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Proceeds from Marketable Debt Securities |  |  |
Proceeds from maturities and sales | $ 5,190,052,000 | $ 2,749,558,000 | $ 2,276,720,000
Realized gains | 6,600,000 | 2,100,000 | 3,900,000
Realized losses | $ (2,100,000) | $ (3,500,000) | $ (2,300,000)

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