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Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Goodwill [Line Items] |  |  |  |
Income tax benefit (expense) |  | $ 1,158.0 | $ 1,425.6 | $ 2,458.7
Accumulated impairment losses related to goodwill |  | 0.0 |  |
Summary of roll forward of the changes in goodwill |  |  |  |
Goodwill, beginning of period |  | 5,706.4 | 4,632.5 |
Increase to goodwill |  | 117.5 | 1,080.1 |
Elimination of goodwill allocated to Hillerød, Denmark manufacturing operations |  | 69.5 | 0.0 |
Other |  | 3.4 | (6.2) |
Goodwill, end of period | $ 5,706.4 | $ 5,757.8 | 5,706.4 | $ 4,632.5
Fumapharm AG | TECFIDERA |  |  |  |
Goodwill [Line Items] |  |  |  |
Income tax benefit (expense) |  |  | 119.9 |
Summary of roll forward of the changes in goodwill |  |  |  |
Increase to goodwill | 300.0 |  | 1,200.0 |
Each additional one billion up to twenty billion | Fumapharm AG | TECFIDERA |  |  |  |
Goodwill [Line Items] |  |  |  |
Cumulative sales level | $ 20,000.0 |  | $ 20,000.0 |

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