XML 188 R124.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Subsequent Events Subsequent events (Details) - Karyopharm - Subsequent Event $ in Millions | Jan. 31, 2018 USD ($)
--- | ---
Subsequent Event [Line Items] |
Upfront And Milestone Payments Made To Collaborative Partner | $ 10.0
Estimated Additional Payments Upon Achievement Of Development And Commercial Milestones | $ 207.0

X
- Definition Estimated additional payments upon achievement of development and commercial milestones. + References No definition available. + Details
Name: | biib_EstimatedAdditionalPaymentsUponAchievementOfDevelopmentAndCommercialMilestones
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Total upfront and milestone payments made to collaborative partner. + References No definition available. + Details
Name: | biib_UpfrontAndMilestonePaymentsMadeToCollaborativePartner
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_TypeOfArrangementAxis=biib_KaryopharmMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |