XML 65 R83.htm IDEA: XBRL DOCUMENT
v3.19.3

Investments in Variable Interest Entities (Details) - USD ($) $ in Millions | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Investment in Variable Interest Entities (Textual) |  |
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities | $ 23.1 | $ 28.7

X
- Definition Investment in biotechnology companies that are determined to be unconsolidated variable interest entities. + References No definition available. + Details
Name: | biib_InvestmentInBiotechnologyCompaniesThatAreDeterminedToBeUnconsolidatedVariableInterestEntities
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Investment in Variable Interest Entities. + References No definition available. + Details
Name: | biib_InvestmentInVariableInterestEntitiesTextualAbstract
Namespace Prefix: | biib_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration