XML 40 R55.htm IDEA: XBRL DOCUMENT
v3.3.0.814

Fair Value Measurements (Details 1) - USD ($) $ in Millions | Sep. 30, 2015 | Dec. 31, 2014
--- | --- | ---
Debt Instrument [Line Items] |  |
Notes payable, carrying value | $ 6,514.3 | $ 583.4
Debt instruments, fair value | 6,680.0 | 647.2
Notes Payable to Fumedica |  |
Debt Instrument [Line Items] |  |
Notes payable, fair value | 9.5 | 12.6
Notes payable, carrying value | 9.1 | 11.7
6.875% Senior Notes due 2018 |  |
Debt Instrument [Line Items] |  |
Notes payable, fair value | 614.0 | 634.6
Notes payable, carrying value | 566.9 | 571.7
2.900% Senior Notes due 2020 |  |
Debt Instrument [Line Items] |  |
Notes payable, fair value | 1,514.1 | 0.0
Notes payable, carrying value | 1,492.3 | 0.0
3.625% Senior Notes due 2022 |  |
Debt Instrument [Line Items] |  |
Notes payable, fair value | 1,008.4 | 0.0
Notes payable, carrying value | 991.9 | 0.0
4.050% Senior Notes due 2025 |  |
Debt Instrument [Line Items] |  |
Notes payable, fair value | 1,767.1 | 0.0
Notes payable, carrying value | 1,733.1 | 0.0
5.200% Senior Notes due 2045 |  |
Debt Instrument [Line Items] |  |
Notes payable, fair value | 1,766.9 | 0.0
Notes payable, carrying value | $ 1,721.0 | $ 0.0

X
- 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=49121117&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=49121117&loc=d3e13476-108611 + Details
Name: | us-gaap_DebtInstrumentFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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 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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13, 16 -Article 9 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 + Details
Name: | us-gaap_NotesPayable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair value portion of notes payable. + References Reference 1: 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
Name: | us-gaap_NotesPayableFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_DebtInstrumentAxis=biib_NotesPayableToFumedicaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=biib_SeniorNotesSixPointEightSevenFivePercentDueTwentyEighteenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=biib_SeniorNotesTwoPointNinePercentDueTwentyTwentyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=biib_SeniorNotesThreePointSixTwoFivePercentDueTwentyTwentyTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=biib_SeniorNotesFourPointZeroFivePercentDueTwentyTwentyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=biib_SeniorNotesFivePointTwoPercentDueTwentyFortyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |