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Collaborative and Other Relationships (Details Textual) $ in Millions, ₩ in Billions | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 31, 2019 | Feb. 29, 2012 USD ($) | Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Sep. 30, 2015 USD ($) | Dec. 31, 2013 USD ($) | Sep. 30, 2013 USD ($) | Mar. 31, 2012 USD ($) | Dec. 31, 2018 | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2012 USD ($) | Feb. 29, 2012 KRW (₩)
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue on sales in the rest of world for RITUXAN |  |  | $ 2,712.4 | $ 2,622.5 | $ 2,639.7 | $ 2,380.1 | $ 2,502.9 | $ 2,539.6 | $ 2,466.0 | $ 2,309.4 |  |  |  |  |  | $ 10,354.7 | $ 9,817.9 | $ 9,188.5 |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,253.6 | 1,973.3 | 2,012.8 |  |
Other revenues |  |  | 179.6 | $ 48.8 | 41.6 | $ 90.0 | 50.9 | 98.6 | 79.0 | $ 87.9 |  |  |  |  |  | 360.0 | 316.4 | 236.1 |  |
Collaboration profit (loss) sharing |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 112.3 | 10.2 | 0.0 |  |
Potential future milestone payments commitment, approximately |  |  | 4,200.0 |  |  |  |  |  |  |  |  |  |  |  |  | 4,200.0 |  |  |  |
Prepaid research and development |  |  | 1,027.5 |  |  |  | $ 1,335.8 |  |  |  |  |  |  |  |  | 1,027.5 | 1,335.8 |  |  |
Equity in loss of investee, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.0 | 0.0 | (12.5) |  |
Roche Group - Genentech |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,316.4 | 1,249.5 | 1,269.8 |  |
Revenue on sales in the rest of world for RITUXAN |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 242.8 | 65.0 | 69.4 |  |
Collaboration Expenses in Dispute |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 120.0 |  |  |  |
AbbVie |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA, including the reimbursement of selling and development expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 16.9 | 21.9 |  |  |
Biogen share of co-promotion profits or losses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00% |  |  |  |
Acorda |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen's share of expense reflected within our consolidation statements of income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 34.0 | 31.5 | 30.6 |  |
Expected additional milestone payments when certain sales threshold is met |  |  | 15.0 |  |  |  |  |  |  |  |  |  |  |  |  | 15.0 |  |  |  |
Foreign sales required to trigger milestone |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.0 |  |  |  |
Ionis Pharmaceuticals, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expected additional milestone payments when certain sales threshold is met |  |  | 800.0 |  |  |  |  |  |  |  |  |  |  |  |  | 800.0 |  |  |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  | $ 75.0 |  |  | 12.0 |  | 10.0 |  |
Estimated additional payments upon achievement of development and commercial milestones. |  |  | 260.0 |  |  |  |  |  |  |  |  |  |  |  |  | 260.0 |  |  |  |
License Fee |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 70.0 |  |  |  |
Expected License Fee And Regulatory Milestone Payments |  |  | 130.0 |  |  |  |  |  |  |  |  |  |  |  |  | 130.0 |  |  |  |
Upfront And Milestone Payments Made To Collaborative Partner |  |  | 25.0 |  |  |  |  |  |  |  |  |  | $ 100.0 |  |  | 25.0 |  |  | $ 30.0 |
Additional milestone payment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 10.0 |
Term of collaboration agreement |  |  |  |  |  |  |  |  |  |  |  |  | 6 years |  |  |  |  |  |  |
Prepaid research and discovery services |  |  |  |  |  |  |  |  |  |  |  |  | $ 25.0 |  |  |  |  |  |  |
Additional milestone payments for product candidate using a different modality |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.0 |  |  |  |
Eisai |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen's share of expense reflected within our consolidation statements of income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 74.3 | 50.5 | 40.4 |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 263.4 | 50.0 |  |  |
Total expense incurred by collaboration |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 146.2 | 95.1 | 84.1 |  |
Additional milestone payment |  |  | 625.0 |  |  |  |  |  |  |  |  |  |  |  |  | 625.0 |  |  |  |
Bristol-Myers Squibb [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  | 300.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional milestone payment |  |  | 410.0 |  |  |  |  |  |  |  |  |  |  |  |  | 410.0 |  |  |  |
iPerian |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional milestone payment |  |  | 490.0 |  |  |  |  |  |  |  |  |  |  |  |  | 490.0 |  |  |  |
Developmental Milestone Payment |  |  |  |  | $ 60.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Alkermes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  | 50.0 |  |  |  |  |  |  |  |  |  |  |  |  | 80.3 |  |  |  |
Upfront And Milestone Payments Made To Collaborative Partner |  |  | 28.0 |  |  |  |  |  |  |  |  |  |  |  |  | 28.0 |  |  |  |
Potential future milestone payments commitment, approximately |  |  | 150.0 |  |  |  |  |  |  |  |  |  |  |  |  | 150.0 |  |  |  |
AGTC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 27.5 | 26.5 | 54.5 |  |
Upfront And Milestone Payments Made To Collaborative Partner |  |  |  |  |  |  |  |  |  |  | $ 124.0 |  |  |  |  |  |  |  |  |
Additional milestone payment |  |  | 1,100.0 |  |  |  |  |  |  |  |  |  |  |  |  | 1,100.0 |  |  |  |
Prepaid research and discovery services |  |  | 11.1 |  |  |  |  |  |  |  | 58.4 |  |  |  |  | 11.1 |  |  |  |
Purchase of common stock |  |  |  |  |  |  |  |  |  |  | 30.0 |  |  |  |  |  |  |  |  |
Total licensing and other fees |  |  |  |  |  |  |  |  |  |  | $ 35.6 |  |  |  |  |  |  |  |  |
University of Pennsylvania |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  |  |  |  | 20.0 |  |  |  |  |  |  | 33.0 | 27.8 |  |  |
Prepaid research and discovery services |  |  | 12.7 |  |  |  |  |  |  |  |  |  |  |  |  | 12.7 |  |  |  |
Potential future milestone payments commitment, approximately |  |  | 2,000.0 |  |  |  |  |  |  |  |  |  |  |  |  | 2,000.0 |  |  |  |
Prepaid research and development |  |  | 29.1 |  |  |  |  |  | $ 15.0 |  |  |  |  |  |  | 29.1 |  |  |  |
Future research and development commitment |  |  | $ 0.0 |  |  |  |  |  |  |  |  |  |  |  |  | 0.0 |  |  |  |
Other research and discovery |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.0 | 10.3 | $ 9.7 |  |
Samsung Biosimilar Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  | $ 46.0 |  |  |  |  |  |  |  |
Collaboration profit (loss) sharing |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 111.0 | $ 15.1 |  |  |
Equity Method Investments, Expected Profit Share |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00% |  |  |  |
RITUXAN |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of Co promotion Operating Profits first fifty million |  |  | 30.00% |  |  |  |  |  |  |  |  |  |  |  |  | 30.00% |  |  |  |
Until First GAZYVA Threshold Date |  |  | 39.00% |  |  |  | 39.00% |  |  |  |  |  |  |  |  | 39.00% | 39.00% |  |  |
Until GAZYVA First Non-CLL FDA Approval |  |  | 40.00% |  |  |  |  |  |  |  |  |  |  |  |  | 40.00% |  | 40.00% |  |
After First Threshold Date and until Second Threshold Date |  |  | 37.50% |  |  |  |  |  |  |  |  |  |  |  |  | 37.50% |  |  |  |
GAZYVA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of Co promotion Operating Profits first fifty million |  |  | 35.00% |  |  |  |  |  |  |  |  |  |  |  |  | 35.00% |  |  |  |
Co-promotion operating profit threshold for Rituxan in U S and Canada to determine share of co promotion operating profit prior to amendment |  |  | $ 50.0 |  |  |  |  |  |  |  |  |  |  |  |  | $ 50.0 |  |  |  |
Limit of gross sale of GAZYVA to be achieved in preceding 12 months under option one |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 150.0 |  |  |  |
Limit of gross sale of GAZYVA to be achieved in any 12 months under option one |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 150.0 |  |  |  |
Sales Trigger Gross Sales Threshold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500.0 |  |  |  |
Until First GAZYVA Threshold Date |  |  | 39.00% |  |  |  |  |  |  |  |  |  |  |  |  | 39.00% |  |  |  |
After First Threshold Date and until Second Threshold Date |  |  | 37.50% |  |  |  |  |  |  |  |  |  |  |  |  | 37.50% |  |  |  |
New Anti-CD20 | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future percentage of co-promotion operating profits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30.00% |  |  |  |
New Anti-CD20 | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future percentage of co-promotion operating profits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 37.50% |  |  |  |
OCREVUS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Royalty operating profit threshold for highest royalty rate percentage |  |  | $ 900.0 |  |  |  |  |  |  |  |  |  |  |  |  | $ 900.0 |  |  |  |
Reduction in royalty rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00% |  |  |  |
Period of collaboration agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11 years |  |  |  |
OCREVUS | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future royalties percentage to be received on sale of ocrelizumab |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13.50% |  |  |  |
OCREVUS | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future royalties percentage to be received on sale of ocrelizumab |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 24.00% |  |  |  |
ZINBRYTA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue on sales in the rest of world for RITUXAN |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 52.7 | $ 7.8 | $ 0.0 |  |
Net impairment charges |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 190.8 |  |  |  |
Unrecorded tax benefit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (93.8) |  |  |  |
ZINBRYTA | AbbVie |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen's share of expense reflected within our consolidation statements of income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 19.9 | 24.3 | 60.8 |  |
SPINRAZA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue on sales in the rest of world for RITUXAN |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 883.7 | 4.6 | 0.0 |  |
SPINRAZA | Ionis Pharmaceuticals, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen's share of expense reflected within our consolidation statements of income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 234.5 | 257.8 | 74.9 |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 29.0 |  |  | 35.3 | 42.8 |  |
Royalty cost of sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 112.4 | 0.5 |  |  |
License Fee |  |  |  |  |  |  |  | $ 75.0 |  |  |  |  |  |  |  |  |  |  |  |
SPINRAZA | Ionis Pharmaceuticals, Inc. | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage Of Royalties As Per Collaboration |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11.00% |  |  |  |
SPINRAZA | Ionis Pharmaceuticals, Inc. | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage Of Royalties As Per Collaboration |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15.00% |  |  |  |
SOD1 | Ionis Pharmaceuticals, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.5 | 20.0 |  |
Lead programs | AGTC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional milestone payment |  |  | 467.5 |  |  |  |  |  |  |  |  |  |  |  |  | $ 467.5 |  |  |  |
Discovery programs | AGTC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional milestone payment |  |  | 592.5 |  |  |  |  |  |  |  |  |  |  |  |  | 592.5 |  |  |  |
Samsung Biosimilar Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 42.7 | 20.2 | 62.9 |  |
Additional milestone payment |  |  | $ 25.0 |  |  |  |  |  |  |  |  |  |  |  |  | $ 25.0 |  |  |  |
Investments By Third Party In Joint Venture As Per Agreement. |  | $ 250.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | ₩ 280.5
Joint Venture Owner Ship Percentage By Third Party. |  | 85.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Method Investments |  | $ 45.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | ₩ 49.5
Percentage of equity interest to the portion of total capital stock |  | 15.00% | 5.00% |  |  |  |  |  |  |  |  |  |  |  |  | 5.00% |  |  |  | 15.00%
Equity Method Investment Ownership Percentage Maximum |  | 49.90% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Research and development | AbbVie |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total expense incurred by collaboration |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 39.9 | 48.6 | 113.8 |  |
Selling, general and administrative | ZINBRYTA | AbbVie |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen's share of expense reflected within our consolidation statements of income |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 22.0 |  |  |
U.S |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue on sales in the rest of world for RITUXAN |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7,017.1 | 7,050.4 | 6,545.8 |  |
Other revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 249.5 | 224.7 | $ 142.0 |  |
U.S | AbbVie |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 16.9 | 21.9 |  |  |
U.S | Eisai |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen share of co-promotion profits or losses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 55.00% |  |  |  |
U.S | SPINRAZA | Ionis Pharmaceuticals, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue on sales in the rest of world for RITUXAN |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 883.7 | 4.6 |  |  |
Outside the U.S | AbbVie |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaboration profit (loss) sharing |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1.3 | 4.9 |  |  |
Outside the U.S | OCREVUS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Future royalties percentage to be received on sale of ocrelizumab |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.00% |  |  |  |
European Union | Eisai |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen share of co-promotion profits or losses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 68.50% |  |  |  |
JAPAN | Eisai |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Biogen share of co-promotion profits or losses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20.00% |  |  |  |
Acquired and in-licensed rights and patents | Ionis Pharmaceuticals, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net change in acquired and in-licensed rights and patents |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 150.0 |  |  |  |
Acquired and in-licensed rights and patents | SPINRAZA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net change in acquired and in-licensed rights and patents |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.0 |  |  |  |
Acquired and in-licensed rights and patents | Biosimilars |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net change in acquired and in-licensed rights and patents |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 25.0 | $ 50.0 |  |  |
Percentage of development expenses to be reimbursed | Eisai |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collaborative and Other Relationships (Textual) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of future development costs related to Eisai | 45.00% |  |  |  |  |  |  |  |  |  |  |  |  |  | 15.00% |  |  |  |  |

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