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BIOGEN INC.

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 2.2.0.7 true Acquisitions and Dispositions (Details) (Biogen Idec Hemophilia Inc. [Member], USD $) 0602 - Disclosure - Acquisitions and Dispositions (Details) true false In Millions false false 1 USD true false false false Biogen Idec Hemophilia Inc. [Member] us-gaap_BusinessAcquisitionAxis xbrldi http://xbrl.org/2006/xbrldi biib_AcquiredCompanyMember us-gaap_BusinessAcquisitionAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 $ 2 2 biib_AcquisitionsAndDispositionsTextualsAbstract biib false na duration Acquisitions and Dispositions. false false false false false true false false false false false verboselabel false 1 false false false false 0 0 false false false xbrli:stringItemType string Acquisitions and Dispositions. false 3 2 us-gaap_BusinessAcquisitionCostOfAcquiredEntityPurchasePrice us-gaap true debit instant No definition available. false false false false false false false false false false false verboselabel false 1 true true false false 40000000 40.0 false false false xbrli:monetaryItemType monetary The total cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, the fair value of the liabilities assumed, and direct costs of the acquisition. Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 141 -Paragraph 51 -Subparagraph d false 1 2 false HundredThousands UnKnown UnKnown false true