Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Pay vs Performance Disclosure
Net income attributable to Biogen Inc.	$ 634.8	$ 583.6	$ 875.3	$ 977.0

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details