v2.4.0.6

Reserves for Discounts and Allowances (Details 1) (USD $) In Millions, unless otherwise specified | Sep. 30, 2012 | Dec. 31, 2011
--- | --- | ---
Summary of total product revenue reserves included in consolidated balance sheets |  |
Reduction of accounts receivable | $ 49.0 | $ 40.6
Component of accrued expenses and other | 160.2 | 115.0
Total reserves | $ 209.2 | $ 155.6

X
- Definition Period balance related to product revenue reserves. + References No definition available. + Details
Name: | biib_ProductRevenueReserves
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Product revenue reserves classified as a reduction of accounts receivable. + References No definition available. + Details
Name: | biib_ProductRevenueReservesClassifiedAsReductionOfAccountsReceivable
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Product revenue reserves classified as a reduction of current liabilities. + References No definition available. + Details
Name: | biib_ProductRevenueReservesClassifiedAsReductionOfCurrentLiabilities
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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