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Acquisitions - (Details) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Business Acquisition [Line Items] |  |  |  |
Acquired in-process research and development |  | $ 0.0 | $ 18.0 | $ 75.0
BIIB118 |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Acquired in-process research and development | $ 75.0 |  |  |

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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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- 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 No definition available. + Details
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Namespace Prefix: | us-gaap_
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |