v2.4.0.6

Business (Details) | 9 Months Ended
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Sep. 30, 2012
Business (Textual) [Abstract] |
Interest in subsidiary (less than given percentage) | 100.00%

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

X
- Definition Interest in subsidiary. + References No definition available. + Details
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Namespace Prefix: | biib_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration