Revenues - Other Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Revenues - Other Revenues (Details) - USD ($) $ in Millions	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,645.5	$ 2,464.9	$ 5,076.5	$ 4,755.4
Contract manufacturing revenue
Disaggregation of Revenue [Line Items]
Total revenue	225.0	100.0	507.3	252.2
Royalty and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	19.6	9.0	30.6	38.6
Contract manufacturing, royalty and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	$ 244.6	$ 109.0	$ 537.9	$ 290.8

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.

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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+ Details

BIOGEN INC. 10-Q