XML 118 R80.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Subsequent Events Subsequent Events (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2018
Subsequent Event [Line Items] |  |  |
Acquired in-process research and development | $ 10.0 | $ 0.0 |
Research and development | $ 496.7 | $ 423.4 |
Pfizer | Subsequent Event |  |  |
Subsequent Event [Line Items] |  |  |
Acquired in-process research and development |  |  | $ 75.0
Estimated additional payments upon achievement of milestones |  |  | $ 515.0
Ionis Pharmaceuticals | Subsequent Event |  |  |
Subsequent Event [Line Items] |  |  |
Term of collaboration agreement |  |  | 10 years
Research and development |  |  | $ 375.0
Purchase of common stock |  |  | $ 500.0
Premium on purchase of common stock |  |  | 25.00%
Total payment to enter collaboration agreement |  |  | $ 1,000.0
Minimum | Ionis Pharmaceuticals | Subsequent Event |  |  |
Subsequent Event [Line Items] |  |  |
Estimated additional payments upon achievement of milestones |  |  | 125.0
Maximum | Ionis Pharmaceuticals | Subsequent Event |  |  |
Subsequent Event [Line Items] |  |  |
Estimated additional payments upon achievement of milestones |  |  | 270.0
Development Milestones [Member] | Pfizer | Subsequent Event |  |  |
Subsequent Event [Line Items] |  |  |
Estimated additional payments upon achievement of milestones |  |  | $ 10.0

X
- Definition Estimated additional payments upon achievement of development and commercial milestones. + References No definition available. + Details
Name: | biib_EstimatedAdditionalPaymentsUponAchievementOfDevelopmentAndCommercialMilestones
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Premium on purchase of common stock + References No definition available. + Details
Name: | biib_Premiumonpurchaseofcommonstock
Namespace Prefix: | biib_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Purchase of common stock + References No definition available. + Details
Name: | biib_Purchaseofcommonstock
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Term of collaboration agreement + References No definition available. + Details
Name: | biib_Termofcollaborationagreement
Namespace Prefix: | biib_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Total payment to enter collaboration agreement + References No definition available. + Details
Name: | biib_Totalpaymenttoentercollaborationagreement
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The costs incurred in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, excluding in-process research and development acquired in a business combination consummated during the period. Excludes software research and development, which has a separate concept. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 730 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373 + Details
Name: | us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount of purchased research and development assets that are acquired in a business combination have no alternative future use and are therefore written off in the period of acquisition. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 730 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
Name: | us-gaap_ResearchAndDevelopmentInProcess
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=biib_PfizerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_TypeOfArrangementAxis=biib_IonisPharmaceuticalsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | biib_FutureContingentMilestoneTypesAxis=biib_DevelopmentMilestonesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |