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Litigation (Details) | 3 Months Ended
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Jun. 30, 2014
Italy |
Loss Contingencies [Line Items] |
Reimbursement limit stated in the resolution | 24 months

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- Definition Reimbursement limit stated in the resolution. + References No definition available. + Details
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Namespace Prefix: | biib_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- 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_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_StatementGeographicalAxis=country_IT
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |