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Intangible Assets and Goodwill (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Intangible assets |  |  |  |  |  |  |  |
Total intangible assets, gross | $ 8,264.6 |  |  |  | $ 7,742.3 | $ 8,264.6 | $ 7,742.3 |
Accumulated Amortization | (4,385.0) |  |  |  | (3,934.0) | (4,385.0) | (3,934.0) |
Intangible assets, net | 3,879.6 |  |  |  | 3,808.3 | 3,879.6 | 3,808.3 |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |  |  |  |
Expected future amortization expense, 2018 | 423.5 |  |  |  |  | 423.5 |  |
Expected future amortization expense, 2019 | 401.8 |  |  |  |  | 401.8 |  |
Expected future amortization expense, 2020 | 381.6 |  |  |  |  | 381.6 |  |
Expected future amortization expense, 2021 | 254.3 |  |  |  |  | 254.3 |  |
Expected future amortization expense, 2022 | 242.3 |  |  |  |  | 242.3 |  |
Amortization of acquired intangible assets |  |  |  |  |  | (814.7) | (385.6) | $ (382.6)
Payment made to Forward Pharma |  |  |  | $ 1,250.0 |  |  |  |
TECFIDERA litigation settlement charge |  |  |  |  | 454.8 | 0.0 | 454.8 | $ 0.0
Out-licensed patents |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Cost | 543.3 |  |  |  | 543.3 | 543.3 | 543.3 |
Accumulated Amortization | (535.6) |  |  |  | (523.6) | (535.6) | (523.6) |
Net | 7.7 |  |  |  | 19.7 | $ 7.7 | 19.7 |
Out-licensed patents | Minimum |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Estimated life, (In Years) |  |  |  |  |  | 13 years |  |
Out-licensed patents | Maximum |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Estimated life, (In Years) |  |  |  |  |  | 23 years |  |
Developed technology |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Cost | 3,005.3 |  |  |  | 3,005.3 | $ 3,005.3 | 3,005.3 |
Accumulated Amortization | (2,689.0) |  |  |  | (2,634.3) | (2,689.0) | (2,634.3) |
Net | 316.3 |  |  |  | 371.0 | $ 316.3 | 371.0 |
Developed technology | Minimum |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Estimated life, (In Years) |  |  |  |  |  | 15 years |  |
Developed technology | Maximum |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Estimated life, (In Years) |  |  |  |  |  | 23 years |  |
Acquired and in-licensed rights and patents |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Cost | 3,971.4 |  |  |  | 3,481.7 | $ 3,971.4 | 3,481.7 |
Accumulated Amortization | (1,160.4) |  |  |  | (776.1) | (1,160.4) | (776.1) |
Net | 2,811.0 |  |  |  | 2,705.6 | $ 2,811.0 | 2,705.6 |
Acquired and in-licensed rights and patents | Minimum |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Estimated life, (In Years) |  |  |  |  |  | 4 years |  |
Acquired and in-licensed rights and patents | Maximum |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Estimated life, (In Years) |  |  |  |  |  | 18 years |  |
In-process research and development |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Indefinite lived intangible assets useful life |  |  |  |  |  | Indefinite |  |
Cost and net | 680.6 |  |  |  | 648.0 | $ 680.6 | 648.0 |
Accumulated Amortization | 0.0 |  |  |  | 0.0 | $ 0.0 | 0.0 |
Trademarks and trade names |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Indefinite lived intangible assets useful life |  |  |  |  |  | Indefinite |  |
Cost and net | 64.0 |  |  |  | 64.0 | $ 64.0 | 64.0 |
Accumulated Amortization | 0.0 |  |  |  | $ 0.0 | 0.0 | 0.0 |
AVONEX | Developed technology |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Net | 309.5 |  |  |  |  | 309.5 |  |
TYSABRI | Acquired and in-licensed rights and patents |  |  |  |  |  |  |  |
Intangible assets |  |  |  |  |  |  |  |
Net | 2,236.2 |  |  |  |  | 2,236.2 |  |
SPINRAZA | Acquired and in-licensed rights and patents |  |  |  |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |  |  |  |
Net change in acquired and in-licensed rights and patents |  |  |  |  |  | 90.0 |  |
Biosimilars | Acquired and in-licensed rights and patents |  |  |  |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |  |  |  |
Net change in acquired and in-licensed rights and patents |  |  |  |  |  | 25.0 | $ 50.0 |
ZINBRYTA |  |  |  |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |  |  |  |
Impairment of out-licensed patent | 31.2 |  |  |  |  |  |  |
TECFIDERA |  |  |  |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |  |  |  |
Amortization of acquired intangible assets | $ (30.8) | $ (30.4) | $ (29.4) | (353.6) |  | $ (444.2) |  |
Net change in acquired and in-licensed rights and patents |  |  |  | $ 795.2 |  |  |  |

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