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Intangible Assets and Goodwill (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2016 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Feb. 12, 2015
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Increase to goodwill |  | $ 1,026.9 | $ 908.1 |  |
Goodwill | $ 3,669.3 | 3,669.3 | 2,663.8 | $ 1,760.2 |
Intangible assets |  |  |  |  |
Total intangible assets, gross | 7,742.3 | 7,742.3 | 7,646.3 |  |
Accumulated Amortization | (3,934.0) | (3,934.0) | (3,561.2) |  |
Intangible assets, net | 3,808.3 | 3,808.3 | 4,085.1 |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
Expected future amortization expense, 2017 | 334.8 | 334.8 |  |  |
Expected future amortization expense, 2018 | 312.7 | 312.7 |  |  |
Expected future amortization expense, 2019 | 295.2 | 295.2 |  |  |
Expected future amortization expense, 2020 | 259.7 | 259.7 |  |  |
Expected future amortization expense, 2021 | 242.8 | 242.8 |  |  |
Amortization of acquired intangible assets |  | (385.6) | (382.6) | (489.8) |
Deferred tax liabilities | 376.6 | 376.6 | 440.1 |  |
Out-licensed patents |  |  |  |  |
Intangible assets |  |  |  |  |
Cost | 543.3 | 543.3 | 543.3 |  |
Accumulated Amortization | (523.6) | (523.6) | (506.0) |  |
Net | 19.7 | $ 19.7 | 37.3 |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
Impairment of out-licensed patent |  |  |  | 34.7 |
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 |  |
Accumulated Amortization | (2,634.3) | (2,634.3) | (2,552.9) |  |
Net | 371.0 | $ 371.0 | 452.4 |  |
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 | 3,481.7 | $ 3,481.7 | 3,303.2 |  |
Accumulated Amortization | (776.1) | (776.1) | (502.3) |  |
Net | 2,705.6 | $ 2,705.6 | 2,800.9 |  |
Acquired and in-licensed rights and patents | Minimum |  |  |  |  |
Intangible assets |  |  |  |  |
Estimated life, (In Years) |  | 6 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 | 648.0 | $ 648.0 | 730.5 |  |
Accumulated Amortization | 0.0 | 0.0 | 0.0 |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
Impairment of out-licensed patent |  | $ 12.2 |  | $ 16.2 |
Trademarks and trade names |  |  |  |  |
Intangible assets |  |  |  |  |
Indefinite lived intangible assets useful life |  | Indefinite |  |  |
Cost and net | 64.0 | $ 64.0 | 64.0 |  |
Accumulated Amortization | 0.0 | 0.0 | 0.0 |  |
AVONEX | Developed technology |  |  |  |  |
Intangible assets |  |  |  |  |
Net | 363.3 | 363.3 |  |  |
TYSABRI | Acquired and in-licensed rights and patents |  |  |  |  |
Intangible assets |  |  |  |  |
Net | 2,493.2 | 2,493.2 |  |  |
SPINRAZA | Acquired and in-licensed rights and patents |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
Net change in acquired and in-licensed rights and patents |  | 60.0 |  |  |
Biosimilars | Acquired and in-licensed rights and patents |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
Net change in acquired and in-licensed rights and patents |  | 50.0 |  |  |
ZINBRYTA | Acquired and in-licensed rights and patents |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
Net change in acquired and in-licensed rights and patents |  | 32.0 |  |  |
ALPROLIX | Acquired and in-licensed rights and patents |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
Net change in acquired and in-licensed rights and patents |  | 26.5 |  |  |
Milestone payment made during period |  | 20.0 |  |  |
Deferred tax liabilities | 6.5 | 6.5 |  |  |
Convergence Pharmaceuticals |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Goodwill |  |  |  |  | $ 128.3
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
In-process research and development |  |  |  |  | $ 424.6
Milestone payment made during period | $ 50.0 |  |  |  |
Fumapharm AG | TECFIDERA |  |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |  |
Increase to goodwill |  | 1,200.0 | $ 900.0 |  |
Rodin Therapeutics | In-process research and development |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
Impairment of out-licensed patent |  | 8.7 |  |  |
Ataxion | In-process research and development |  |  |  |  |
Intangible Assets and Goodwill (Additional Textual) |  |  |  |  |
Impairment of out-licensed patent |  | $ 3.5 |  |  |

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