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Financial Instruments (Tables) | 12 Months Ended
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Dec. 31, 2013
Investments, All Other Investments [Abstract] |
Marketable securities including strategic investments |
As of December 31, 2013 (In millions) | Fair Value |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Amortized Cost
Available-for-sale: |  |  |  |  |  |  |
Corporate debt securities |  |  |  |  |  |  |
Current | $ | 100.7 |  |  | $ | — |  |  | $ | — |  |  | $ | 100.7 |
Non-current | 339.1 |  |  | 0.4 |  |  | (0.1 | ) |  | 338.8 |
Government securities |  |  |  |  |  |  |
Current | 519.5 |  |  | — |  |  | — |  |  | 519.5 |
Non-current | 155.2 |  |  | — |  |  | (0.1 | ) |  | 155.3 |
Mortgage and other asset backed securities |  |  |  |  |  |  |
Current | — |  |  | — |  |  | — |  |  | — |
Non-current | 131.4 |  |  | — |  |  | (0.1 | ) |  | 131.5 |
Total marketable debt securities | $ | 1,245.9 |  |  | $ | 0.4 |  |  | $ | (0.3 | ) |  | $ | 1,245.8 |
Marketable equity securities, non-current | $ | 11.2 |  |  | $ | 8.7 |  |  | $ | — |  |  | $ | 2.5 |
As of December 31, 2012 (In millions) | Fair Value |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Amortized Cost
Available-for-sale: |  |  |  |  |  |  |
Corporate debt securities |  |  |  |  |  |  |
Current | $ | 346.9 |  |  | $ | 0.3 |  |  | $ | — |  |  | $ | 346.6 |
Non-current | 654.1 |  |  | 2.8 |  |  | (0.6 | ) |  | 651.9 |
Government securities |  |  |  |  |  |  |
Current | 783.4 |  |  | 0.3 |  |  | — |  |  | 783.1 |
Non-current | 874.4 |  |  | 0.8 |  |  | — |  |  | 873.6 |
Mortgage and other asset backed securities |  |  |  |  |  |  |
Current | 4.8 |  |  | — |  |  | — |  |  | 4.8 |
Non-current | 508.1 |  |  | 1.4 |  |  | (1.3 | ) |  | 508.0 |
Total marketable debt securities | $ | 3,171.7 |  |  | $ | 5.6 |  |  | $ | (1.9 | ) |  | $ | 3,168.0 |
Marketable equity securities, non-current | $ | 9.0 |  |  | $ | 3.0 |  |  | $ | — |  |  | $ | 6.0 |
Summary of financial assets with maturities of less than 90 days included within cash and cash equivalents |
| As of December 31,
(In millions) | 2013 |  | 2012
Commercial paper | $ | 1.2 |  |  | $ | 40.7 |
Overnight reverse repurchase agreements | 22.4 |  |  | 67.4 |
Short-term debt securities | 401.1 |  |  | 331.3 |
Total | $ | 424.7 |  |  | $ | 439.4 |
Summary of contractual maturities: Available-for-sale securities |
| As of December 31, 2013 |  | As of December 31, 2012
(In millions) | Estimated Fair Value |  | Amortized Cost |  | Estimated Fair Value |  | Amortized Cost
Due in one year or less | $ | 620.2 |  |  | $ | 620.2 |  |  | $ | 1,135.0 |  |  | $ | 1,134.5 |
Due after one year through five years | 573.1 |  |  | 572.9 |  |  | 1,744.3 |  |  | 1,741.2 |
Due after five years | 52.6 |  |  | 52.7 |  |  | 292.4 |  |  | 292.3 |
Total available-for-sale securities | $ | 1,245.9 |  |  | $ | 1,245.8 |  |  | $ | 3,171.7 |  |  | $ | 3,168.0 |
Proceeds from marketable securities, excluding strategic investments |
| For the Years Ended December 31,
(In millions) | 2013 |  | 2012 |  | 2011
Proceeds from maturities and sales | $ | 5,190.1 |  |  | $ | 2,749.6 |  |  | $ | 2,276.7 |
Realized gains | $ | 6.6 |  |  | $ | 2.1 |  |  | $ | 3.9 |
Realized losses | $ | 2.1 |  |  | $ | 3.5 |  |  | $ | 2.3 |

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