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Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Goodwill [Line Items] |  |  |  |
Increase in goodwill |  |  | $ 540.9 |
Income tax expense (benefit) | $ 263.7 | $ 269.6 | 586.2 | $ 508.8
Summary of roll forward of the changes in goodwill |  |  |  |
Goodwill, beginning of period |  |  | 4,632.5 |
Other |  |  | (3.1) |
Goodwill, end of period | $ 5,170.3 |  | 5,170.3 |
TECFIDERA | Fumapharm AG |  |  |  |
Goodwill [Line Items] |  |  |  |
Increase in goodwill |  |  | 600.0 |
Income tax expense (benefit) |  |  | $ 59.1 |

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