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v3.22.4

Collaborative and Other Relationships - Pretax Profit Sharing Formula (Details) - GAZYVA | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
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Collaborative arrangements and non-collaborative arrangement transactions |  |  |
Until Second GAZYVA Threshold Date | 37.50% | 37.50% | 37.50%
After Second GAZYVA Threshold Date | 35.00% |  |

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- Definition Percentage of co promotion operating profits greater than first fifty million option two sub option three. + References No definition available. + Details
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Namespace Prefix: | biib_
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Balance Type: | na
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X
- Definition Percentage of co promotion operating profits greater than first fifty million option two sub option two. + References No definition available. + Details
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Namespace Prefix: | biib_
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Balance Type: | na
Period Type: | instant

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- 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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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