v3.25.3
Segment Information - Additional Segment Information (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Segment Reporting, Asset Reconciling Item [Line Items]        
Total revenue $ 2,534.7 $ 2,465.8 $ 7,611.2 $ 7,221.2
Cost of sales, excluding amortization and impairment of acquired intangible assets 674.4 638.7 1,908.7 1,726.9
Research and development: 436.1 516.2 1,269.2 1,467.0
Acquired in-process research and development, upfront and milestone expense 2.1 26.5 249.4 42.5
Selling, general and administrative 594.8 588.4 1,751.1 1,723.7
Net income attributable to Biogen Inc. 466.5 388.5 1,341.8 1,365.5
Product revenue, net        
Segment Reporting, Asset Reconciling Item [Line Items]        
Total revenue 1,846.9 1,769.4 5,452.1 5,380.9
Royalty and other revenue        
Segment Reporting, Asset Reconciling Item [Line Items]        
Total revenue 9.7 9.7 40.3 48.3
Reportable Segment        
Segment Reporting, Asset Reconciling Item [Line Items]        
Total revenue 2,534.7 2,465.8 7,611.2 7,221.2
Other segment expense 360.8 307.5 1,091.0 895.6
Net income attributable to Biogen Inc. 466.5 388.5 1,341.8 1,365.5
Reportable Segment | Research and discovery        
Segment Reporting, Asset Reconciling Item [Line Items]        
Research and development: 41.0 48.3 131.9 141.6
Reportable Segment | Early stage programs        
Segment Reporting, Asset Reconciling Item [Line Items]        
Research and development: 59.9 64.1 184.2 214.8
Reportable Segment | Late stage programs        
Segment Reporting, Asset Reconciling Item [Line Items]        
Research and development: 60.4 56.3 154.4 135.6
Reportable Segment | Marketed products        
Segment Reporting, Asset Reconciling Item [Line Items]        
Research and development: 107.7 126.0 284.9 414.1
Reportable Segment | Other research and development costs        
Segment Reporting, Asset Reconciling Item [Line Items]        
Research and development: 167.1 221.5 513.8 560.9
Reportable Segment | Product revenue, net        
Segment Reporting, Asset Reconciling Item [Line Items]        
Cost of sales, excluding amortization and impairment of acquired intangible assets 384.0 468.2 1,261.2 1,204.3
Reportable Segment | Royalty and other revenue        
Segment Reporting, Asset Reconciling Item [Line Items]        
Cost of sales, excluding amortization and impairment of acquired intangible assets $ 290.4 $ 170.5 $ 647.5 $ 522.6