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Share-Based Payments (Details 2) | 9 Months Ended
--- | ---
Sep. 30, 2014 | Sep. 30, 2013
Market stock units |  |
Schedule of stock option grants |  |
Stock units | 236,000 | 268,000
Cash settled performance shares |  |
Schedule of stock option grants |  |
Stock units | 182,000 | 273,000
Performance units |  |
Schedule of stock option grants |  |
Stock units | 57,000 | 0
Time-vested restricted stock units |  |
Schedule of stock option grants |  |
Stock units | 437,000 | 708,000

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

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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration