Biogen share of co-promotion profits or losses

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- Definition

Collaboration profit (loss) sharing

+ References

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- Definition

Percentage of future development costs related to Eisai

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- Definition

Total costs related to goods produced and sold during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(a))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Amount, after sales adjustments, returns, allowances, and discounts, of revenue classified as other.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(a),(d))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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The costs incurred in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, excluding in-process research and development acquired in a business combination consummated during the period. Excludes software research and development, which has a separate concept.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

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Collaborative and Other Relationships Collaborative and Other Relationships - Collaborations (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Inventory charges		$ 446.0	$ 384.6
Research and development		496.7	423.4
Other		164.4	90.0
Collaboration profit (loss) sharing		42.5	20.8
ZINBRYTA
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Inventory charges		2.4
Research and development		$ 12.8
AbbVie
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Biogen share of co-promotion profits or losses		50.00%
Eisai \| E2609 and BAN2401
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development		$ 26.1	20.8
Eisai \| Aducanumab
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development		63.6	53.3
Scenario, Forecast \| Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of future development costs related to Eisai	45.00%			15.00%
U.S. \| AbbVie
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Other		4.9	$ 5.9
E.U. and Canada \| AbbVie
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration profit (loss) sharing		$ 1.3