v3.25.2
Revenues - Revenues from Anti-CD20 Therapeutic Programs (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Disaggregation of Revenue [Line Items]        
Total revenues from anti-CD20 therapeutic programs $ 2,645.5 $ 2,464.9 $ 5,076.5 $ 4,755.4
Genentech        
Disaggregation of Revenue [Line Items]        
Biogen's share of pre-tax profits in the U.S. for RITUXAN and GAZYVA 107.7 103.4 191.4 190.5
Other revenues from anti-CD20 therapeutic programs 5.8 4.8 11.5 9.0
Revenue from anti-CD20 therapeutic programs        
Disaggregation of Revenue [Line Items]        
Total revenues from anti-CD20 therapeutic programs 467.3 444.5 845.5 838.5
Royalty Attributed To OCREVUS        
Disaggregation of Revenue [Line Items]        
Total revenues from anti-CD20 therapeutic programs $ 353.8 $ 336.3 $ 642.6 $ 639.0