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Financial Instruments (Details 3) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Proceeds from Marketable Debt Securities |  |  |
Proceeds from maturities and sales | $ 7,378.9 | $ 4,063.0 | $ 2,718.9
Realized gains | 3.3 | 1.5 | 0.7
Realized losses | $ (4.3) | $ (3.5) | $ (0.5)

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