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Subsequent Events (Details) - InnoCare Pharma Limited (InnoCare) Agreement - Subsequent Event - Forecast $ in Millions | 6 Months Ended
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Dec. 31, 2021 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |
Upfront and milestone payments made to collaborative partner | $ 125.0
Potential future milestone payments commitment to third party | $ 812.5

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- Definition Potential future milestone payments commitment to third party approximately. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Total upfront and milestone payments made to collaborative partner. + References No definition available. + Details
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Namespace Prefix: | biib_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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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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Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
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Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
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- Details
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