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Intangible Assets and Goodwill (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Jun. 07, 2019 | Dec. 31, 2018
Intangible assets |  |  |  |  |  |
Contingent consideration impairment | $ 57.8 | $ 87.9 | $ 66.3 | $ 91.6 |  |
Total intangible assets, gross | 8,206.1 |  | 8,206.1 |  |  | $ 7,727.3
Accumulated Amortization | (4,813.7) |  | (4,813.7) |  |  | (4,607.3)
Intangible assets, net | 3,392.4 |  | 3,392.4 |  |  | 3,120.0
Amortization and impairment of acquired intangible assets | 283.9 | 281.9 | 422.2 | 493.2 |  |
Amortization of intangible assets, excluding impairment | 68.0 | 92.6 | 206.3 | 303.9 |  |
Intangible Assets and Goodwill (Textual) [Abstract] |  |  |  |  |  |
Expected future amortization expense, 2019 (remaining three months) | 65.0 |  | 65.0 |  |  |
Expected future amortization expense, 2020 | 255.0 |  | 255.0 |  |  |
Expected future amortization expense, 2021 | 215.0 |  | 215.0 |  |  |
Expected future amortization expense, 2022 | 215.0 |  | 215.0 |  |  |
Expected future amortization expense, 2023 | 220.0 |  | 220.0 |  |  |
Expected future amortization expense, 2024 | 210.0 |  | 210.0 |  |  |
Out-licensed patents |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Cost | 543.3 |  | 543.3 |  |  | 543.3
Net | 0.8 |  | 0.8 |  |  | 1.0
Accumulated Amortization | (542.5) |  | $ (542.5) |  |  | (542.3)
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
Net | 240.7 |  | 240.7 |  |  | 270.5
Accumulated Amortization | (2,764.6) |  | $ (2,764.6) |  |  | (2,734.8)
Developed technology | Minimum |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Estimated life, (in years) |  |  | 15 years |  |  |
Developed technology | Maximum |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Estimated life, (in years) |  |  | 28 years |  |  |
Developed technology | AVONEX |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Net | 236.6 |  | $ 236.6 |  |  |
Acquired and in-licensed rights and patents |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Cost | 3,638.7 |  | 3,638.7 |  |  | 3,638.7
Net | 2,132.1 |  | 2,132.1 |  |  | 2,308.5
Accumulated Amortization | (1,506.6) |  | $ (1,506.6) |  |  | (1,330.2)
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 |  |  |
Acquired and in-licensed rights and patents | TYSABRI |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Net | 1,889.6 |  | $ 1,889.6 |  |  |
Acquired and in-licensed rights and patents | TECFIDERA |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Net | 45.6 |  | $ 45.6 |  |  |
In Process Research and Development |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Indefinite lived intangible assets useful life |  |  | Indefinite until commercialization |  |  |
Cost and Net | 954.8 |  | $ 954.8 |  |  | 476.0
Accumulated Amortization | 0.0 |  | $ 0.0 |  |  | 0.0
Amortization and impairment of acquired intangible assets | 215.9 | 189.3 |  |  |  |
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
Nightstar |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
In-process research and development |  |  |  |  | $ 700.0 |
BG00011 |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Contingent consideration impairment | 61.2 |  |  |  |  |
BG00011 | In Process Research and Development |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Amortization and impairment of acquired intangible assets | $ 215.9 |  |  |  |  |
PLSR [Member] | In Process Research and Development |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Amortization and impairment of acquired intangible assets |  | 60.0 |  |  |  |
TGN [Member] |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Contingent consideration impairment |  | 89.6 |  |  |  |
TGN [Member] | In Process Research and Development |  |  |  |  |  |
Intangible assets |  |  |  |  |  |
Cost and Net |  | 41.8 |  | $ 41.8 |  |
Amortization and impairment of acquired intangible assets |  | $ 129.3 |  |  |  |

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