v2.4.0.6

Segment Information (Details) | 9 Months Ended
--- | ---
Sep. 30, 2012 segment
Segment Information (Textual) [Abstract] |
Number of reportable segment | 1

X
- Definition Number Of Reportable Segment. + References No definition available. + Details
Name: | biib_NumberOfReportableSegment
Namespace Prefix: | biib_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | biib_SegmentInformationTextualAbstract
Namespace Prefix: | biib_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration