XML 174 R110.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Investments in Variable Interest Entities (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Oct. 31, 2017 | Sep. 30, 2015 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Variable Interest Entity [Line Items] |  |  |  |  |
Payment to Neurimmune |  |  | $ 134.1 | $ 0.0 | $ 56.1
Investment in Variable Interest Entities (Textual) |  |  |  |  |
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities |  |  | 48.3 | $ 47.4 |
Neurimmune |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Payment to Neurimmune | $ 150.0 | $ 60.0 |  |  |
Reduction in royalty rate payable on commercial sales | 15.00% |  |  |  |
Additional reduction in royalty rate payable on commercial sales | 5.00% |  |  |  |
Additional potential payment to Neurimmune | $ 50.0 |  |  |  |
Investment in Variable Interest Entities (Textual) |  |  |  |  |
Remaining potential development milestone payments and royalties on commercial sales under the terms of collaboration agreement |  |  | $ 275.0 |  |

X
- Definition Additional Potential Payments to Noncontrolling Interest + References No definition available. + Details
Name: | biib_AdditionalPotentialPaymentstoNoncontrollingInterest
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Additional reduction in royalty rate payable on commercial sales + References No definition available. + Details
Name: | biib_Additionalreductioninroyaltyratepayableoncommercialsales
Namespace Prefix: | biib_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Investment in biotechnology companies that are determined to be unconsolidated variable interest entities. + References No definition available. + Details
Name: | biib_InvestmentInBiotechnologyCompaniesThatAreDeterminedToBeUnconsolidatedVariableInterestEntities
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Investment in Variable Interest Entities. + References No definition available. + Details
Name: | biib_InvestmentInVariableInterestEntitiesTextualAbstract
Namespace Prefix: | biib_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Reduction in royalty rate payable on commercial sales + References No definition available. + Details
Name: | biib_Reductioninroyaltyratepayableoncommercialsales
Namespace Prefix: | biib_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Expected total payments including upfront and milestone payments as well as the greater of an annual maintenance fee or usage-based royalty payments under the terms of collaboration agreement. + References No definition available. + Details
Name: | biib_RemainingPotentialDevelopmentMilestonePaymentsAndRoyaltiesOnCommercialSalesUnderTermsOfCollaborationAgreement
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of cash outflow to a noncontrolling interest. Includes, but not limited to, reduction of noncontrolling interest ownership. Excludes dividends paid to the noncontrolling interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585 + Details
Name: | us-gaap_PaymentsToMinorityShareholders
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_VariableInterestEntityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=biib_NeurimmuneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |