XML 121 R57.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Summary of Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Business (Textual) |  |  |
Interest in subsidiary (less than given percentage) | 100.00% |  |
Payment terms of accounts receivable arising from product sales | 30 to 90 days |  |
Estimated useful lives of leasehold improvements | Lesser of the useful life or the term of the respective lease |  |
Purchase price of common stock under ESPP | 85% of the lower of (i) the fair market value per share of the common stock on the first business day of an offering period and (ii) the fair market value per share of the common stock on the purchase date |  |
Percentage of market value per share of common stock |  | $ 0.85 |
Compensation expense over purchase period | The fair value of the look-back provision plus the 15% discount |  |
Discount rate recognized in compensation expense |  | 15.00% |
Advertising costs | $ 75.2 | $ 106.3 | $ 108.6
Minimum | Building |  |  |
Property, Plant and Equipment |  |  |
Property, plant and equipment, useful life | 15 years |  |
Minimum | Furniture and Fixtures |  |  |
Property, Plant and Equipment |  |  |
Property, plant and equipment, useful life | 5 years |  |
Minimum | Machinery and Equipment |  |  |
Property, Plant and Equipment |  |  |
Property, plant and equipment, useful life | 5 years |  |
Minimum | Computer Equipment |  |  |
Property, Plant and Equipment |  |  |
Property, plant and equipment, useful life | 3 years |  |
Maximum | Building |  |  |
Property, Plant and Equipment |  |  |
Property, plant and equipment, useful life | 40 years |  |
Maximum | Furniture and Fixtures |  |  |
Property, Plant and Equipment |  |  |
Property, plant and equipment, useful life | 7 years |  |
Maximum | Machinery and Equipment |  |  |
Property, Plant and Equipment |  |  |
Property, plant and equipment, useful life | 20 years |  |
Maximum | Computer Equipment |  |  |
Property, Plant and Equipment |  |  |
Property, plant and equipment, useful life | 5 years |  |
Distributor One |  |  |
Property, Plant and Equipment |  |  |
Percentage receivables of wholesale distributor accounted in consolidated receivables | 26.50% | 37.20% |
Distributor Two |  |  |
Property, Plant and Equipment |  |  |
Percentage receivables of wholesale distributor accounted in consolidated receivables | 19.00% | 19.20% |
Deferred Tax Asset |  |  |
Property, Plant and Equipment |  |  |
Cumulative Effect of New Accounting Principle in Period of Adoption | $ 500.0 |  |
Retained Earnings |  |  |
Property, Plant and Equipment |  |  |
Cumulative Effect of New Accounting Principle in Period of Adoption | $ 500.0 |  |

X
- Definition Business. + References No definition available. + Details
Name: | biib_BusinessTextualAbstract
Namespace Prefix: | biib_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Compensation expense over purchase period. + References No definition available. + Details
Name: | biib_CompensationExpenseOverPurchasePeriod
Namespace Prefix: | biib_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Discount rate recognized in compensation expense. + References No definition available. + Details
Name: | biib_DiscountRateRecognizedInCompensationExpense
Namespace Prefix: | biib_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Estimated useful lives of leasehold improvements. + References No definition available. + Details
Name: | biib_EstimatedUsefulLivesOfLeaseholdImprovements
Namespace Prefix: | biib_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Interest in subsidiary. + References No definition available. + Details
Name: | biib_InterestInSubsidiary
Namespace Prefix: | biib_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Payment terms of accounts receivable. + References No definition available. + Details
Name: | biib_PaymentTermsOfAccountsReceivable
Namespace Prefix: | biib_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of market value per share of common stock. + References No definition available. + Details
Name: | biib_PercentageOfMarketValuePerShareOfCommonStock
Namespace Prefix: | biib_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage receivables of wholesale distributor accounted in consolidated receivables. + References No definition available. + Details
Name: | biib_PercentageReceivablesOfWholesaleDistributorAccountedInConsolidatedReceivables
Namespace Prefix: | biib_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Purchase Price Of Common Stock Under ESPP. + References No definition available. + Details
Name: | biib_PurchasePriceOfCommonStockUnderEspp
Namespace Prefix: | biib_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 720 -SubTopic 35 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848 + Details
Name: | us-gaap_AdvertisingExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption. + References No definition available. + Details
Name: | us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption
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_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_FurnitureAndFixturesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_MachineryAndEquipmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_ComputerEquipmentMember
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_MajorDistributorAxis=biib_DistributorOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | biib_MajorDistributorAxis=biib_DistributorTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_DeferredTaxAssetDomain
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_RetainedEarningsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |