XML 127 R103.htm IDEA: XBRL DOCUMENT
v3.25.2

Collaborative and Other Relationships - Summary of Activity Related to LEQEMBI Collaboration (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
LEQEMBI | Alzheimer's collaboration revenue |  |  |  |
Collaborative arrangements and non-collaborative arrangement transactions |  |  |  |
Total development expense incurred by the collaboration related to the advancement of LEQEMBI | $ 54.9 | $ 90.6 |  |
Expense reflected within statements of income | 27.5 | 45.4 |  |
LEQEMBI | Alzheimer's collaboration revenue | Selling, general and administrative |  |  |  |
Collaborative arrangements and non-collaborative arrangement transactions |  |  |  |
Expense reflected within statements of income | 85.7 | 68.9 |  |
Expense incurred by the collaboration | $ 171.2 | $ 137.7 |  |
E2609 and BAN2401 | Eisai |  |  |  |
Collaborative arrangements and non-collaborative arrangement transactions |  |  |  |
Total development expense incurred by the collaboration related to the advancement of LEQEMBI |  |  | $ 107.5 | $ 177.9
Expense reflected within statements of income |  |  | 53.8 | 89.0
E2609 and BAN2401 | Eisai | Selling, general and administrative |  |  |  |
Collaborative arrangements and non-collaborative arrangement transactions |  |  |  |
Expense reflected within statements of income |  |  | 174.5 | 155.8
Expense incurred by the collaboration |  |  | $ 348.9 | $ 311.6

X
- Definition Total expense incurred by collaboration. + References No definition available. + Details
Name: | biib_ExpenseIncurredByCollaboration
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Expense incurred by the collaboration + References No definition available. + Details
Name: | biib_Expenseincurredbythecollaboration
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Expense reflected within statements of income + References No definition available. + Details
Name: | biib_Expensereflectedwithinstatementsofincome
Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 808 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479402/808-10-50-1 + Details
Name: | us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_ProductOrServiceAxis=biib_LEQEMBIMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_SellingGeneralAndAdministrativeExpensesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=biib_E2609andBAN2401Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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