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Quarterly Financial Data (Unaudited) (Details Textual) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2014 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Schedule Of Development Milestone And Collaboration [Line Items] |  |  |  |  |  |  |  |  |  |
Restructuring charges |  |  |  |  |  |  |  | $ 33.1 | $ 93.4 | $ 0.0
Research and development |  |  |  |  |  |  |  | 1,973.3 | 2,012.8 | 1,893.4
TECFIDERA litigation settlement and license charges |  |  |  |  |  |  |  | 454.8 | 0.0 | 0.0
Net (loss) income attributable to noncontrolling interests, net of tax |  |  |  |  |  |  |  | (7.1) | 46.2 | $ 6.8
Eisai |  |  |  |  |  |  |  |  |  |
Schedule Of Development Milestone And Collaboration [Line Items] |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  |  | $ 21.6 | 50.0 |  |
AGTC |  |  |  |  |  |  |  |  |  |
Schedule Of Development Milestone And Collaboration [Line Items] |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  | $ 48.1 |  | 26.5 | $ 54.5 |
Mitsubishi Tanabe Pharma Corporation |  |  |  |  |  |  |  |  |  |
Schedule Of Development Milestone And Collaboration [Line Items] |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  | $ 60.0 |  |  | 22.8 |  |
Neurimmune |  |  |  |  |  |  |  |  |  |
Schedule Of Development Milestone And Collaboration [Line Items] |  |  |  |  |  |  |  |  |  |
Net (loss) income attributable to noncontrolling interests, net of tax |  |  |  |  |  | $ 60.0 |  |  |  |
2015 Restructuring Charges |  |  |  |  |  |  |  |  |  |
Schedule Of Development Milestone And Collaboration [Line Items] |  |  |  |  |  |  |  |  |  |
Restructuring charges |  |  |  | $ 9.7 | $ 93.4 |  |  | 8.0 |  |
Cambridge, MA |  |  |  |  |  |  |  |  |  |
Schedule Of Development Milestone And Collaboration [Line Items] |  |  |  |  |  |  |  |  |  |
Accelerated depreciation | $ 14.0 | $ 15.7 | $ 15.8 |  |  |  |  | $ 45.5 |  |
SPINRAZA | Ionis Pharmaceuticals, Inc. [Member] |  |  |  |  |  |  |  |  |  |
Schedule Of Development Milestone And Collaboration [Line Items] |  |  |  |  |  |  |  |  |  |
License Fee |  | $ 75.0 |  |  |  |  |  |  |  |

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