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Collaborative and Other Relationships Collaborative and Other Relationships - Equity Method Investments (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
Feb. 29, 2012 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Collaboration profit (loss) sharing |  | $ 39.2 | $ 26.5 | $ 81.7 | $ 47.3
Other revenues |  | $ (3,356.5) | (3,078.4) | $ (6,487.6) | (5,889.1)
Samsung Bioepis |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Percentage of stake in entity |  | 5.00% |  | 5.00% |
Percentage of stake in entity maximum | 49.90% |  |  |  |
Payments to acquire additional investment in equity method investment |  | $ 700.0 |  |  |
Biogen share of co-promotion profits or losses |  |  |  | 50.00% |
Collaboration profit (loss) sharing |  | 39.7 | 25.2 | $ 83.5 | 46.0
Collaborative arrangement | Samsung Bioepis |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |
Other revenues |  | $ (14.7) | $ (12.7) | $ (32.6) | $ (14.9)

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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 + Details
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