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v2.4.1.9

Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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Summary of fair and carrying value of debt instruments |  |
Notes payable, carrying value | $ 583.9 us-gaap_NotesPayable | $ 585.2 us-gaap_NotesPayable
Debt instruments, fair value | 646.8 us-gaap_DebtInstrumentFairValue | 647.2 us-gaap_DebtInstrumentFairValue
Notes Payable to Fumedica |  |
Summary of fair and carrying value of debt instruments |  |
Notes payable, fair value | 12.9 us-gaap_NotesPayableFairValueDisclosure / us-gaap_DebtInstrumentAxis = biib_NotesPayableToFumedicaMember | 12.6 us-gaap_NotesPayableFairValueDisclosure / us-gaap_DebtInstrumentAxis = biib_NotesPayableToFumedicaMember
Notes payable, carrying value | 12.1 us-gaap_NotesPayable / us-gaap_DebtInstrumentAxis = biib_NotesPayableToFumedicaMember | 11.7 us-gaap_NotesPayable / us-gaap_DebtInstrumentAxis = biib_NotesPayableToFumedicaMember
6.875% Senior Notes due 2018 |  |
Summary of fair and carrying value of debt instruments |  |
Notes payable, fair value | 633.9 us-gaap_NotesPayableFairValueDisclosure / us-gaap_DebtInstrumentAxis = biib_SeniorNotesSixPointEightSevenFivePercentDueTwentyEighteenMember | 634.6 us-gaap_NotesPayableFairValueDisclosure / us-gaap_DebtInstrumentAxis = biib_SeniorNotesSixPointEightSevenFivePercentDueTwentyEighteenMember
Notes payable, carrying value | $ 571.8 us-gaap_NotesPayable / us-gaap_DebtInstrumentAxis = biib_SeniorNotesSixPointEightSevenFivePercentDueTwentyEighteenMember | $ 573.5 us-gaap_NotesPayable / us-gaap_DebtInstrumentAxis = biib_SeniorNotesSixPointEightSevenFivePercentDueTwentyEighteenMember

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- Definition Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13476-108611 + Details
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- Definition Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13, 16 -Article 9 + Details
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- Definition Fair value portion of notes payable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19,20,22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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