XML 84 R41.htm IDEA: XBRL DOCUMENT v2.4.0.6

Business (Details)	3 Months Ended
Business (Details)	Mar. 31, 2012
Business (Textual) [Abstract]
Interest in subsidiary (less than given percentage)	100.00%

X

- Details

Name:	biib_BusinessTextualAbstract
Namespace Prefix:	biib_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Interest in subsidiary.

+ References

No definition available.

+ Details

Name:	biib_InterestInSubsidiary
Namespace Prefix:	biib_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration