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Financial Instruments (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2014 | Dec. 31, 2013
--- | --- | ---
Marketable Debt and Equity Securities |  |
Fair Value | $ 1,155.8 | $ 1,245.9
Gross Unrealized Gains | 0.7 | 0.4
Gross Unrealized Losses | (0.5) | (0.3)
Amortized Cost | 1,155.6 | 1,245.8
Corporate debt securities Current |  |
Marketable Debt and Equity Securities |  |
Fair Value | 135.7 | 100.7
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | 0
Amortized Cost | 135.7 | 100.7
Corporate debt securities Non-current |  |
Marketable Debt and Equity Securities |  |
Fair Value | 401.2 | 339.1
Gross Unrealized Gains | 0.5 | 0.4
Gross Unrealized Losses | (0.2) | (0.1)
Amortized Cost | 400.9 | 338.8
Government securities Current |  |
Marketable Debt and Equity Securities |  |
Fair Value | 295.9 | 519.5
Gross Unrealized Gains | 0.1 | 0
Gross Unrealized Losses | 0 | 0
Amortized Cost | 295.8 | 519.5
Government securities Non-current |  |
Marketable Debt and Equity Securities |  |
Fair Value | 170.8 | 155.2
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (0.1) | (0.1)
Amortized Cost | 170.9 | 155.3
Mortgage and other asset backed securities Current |  |
Marketable Debt and Equity Securities |  |
Fair Value | 0 | 0
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | 0
Amortized Cost | 0 | 0
Mortgage and other asset backed securities Non-current |  |
Marketable Debt and Equity Securities |  |
Fair Value | 152.2 | 131.4
Gross Unrealized Gains | 0.1 | 0
Gross Unrealized Losses | (0.2) | (0.1)
Amortized Cost | 152.3 | 131.5
Marketable equity securities |  |
Marketable Debt and Equity Securities |  |
Fair Value | 13.8 | 11.2
Gross Unrealized Gains | 11.4 | 8.7
Gross Unrealized Losses | (0.1) | 0
Amortized Cost | $ 2.5 | $ 2.5

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