v3.25.3
Revenues - Revenues by product (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Disaggregation of Revenue [Line Items]        
Total revenue $ 2,534.7 $ 2,465.8 $ 7,611.2 $ 7,221.2
Product revenue, net        
Disaggregation of Revenue [Line Items]        
Total revenue 1,846.9 1,769.4 5,452.1 5,380.9
Product revenue, net | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 935.3 813.0 2,630.2 2,405.8
Product revenue, net | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 911.6 956.4 2,821.9 2,975.1
MS Product Revenues        
Disaggregation of Revenue [Line Items]        
Total revenue 1,061.5 1,053.9 3,121.7 3,279.6
MS Product Revenues | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 642.9 546.0 1,790.7 1,631.6
MS Product Revenues | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 418.6 507.9 1,331.0 1,648.0
Fumarate        
Disaggregation of Revenue [Line Items]        
Total revenue 382.8 390.9 1,133.6 1,190.7
Fumarate | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 234.2 175.0 626.3 512.9
Fumarate | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 148.6 215.9 507.3 677.8
TECFIDERA        
Disaggregation of Revenue [Line Items]        
Total revenue 168.2 232.8 567.9 739.3
TECFIDERA | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 44.6 40.1 131.6 127.9
TECFIDERA | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 123.6 192.7 436.3 611.4
VUMERITY        
Disaggregation of Revenue [Line Items]        
Total revenue 214.6 158.1 565.7 451.4
VUMERITY | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 189.6 134.9 494.7 385.0
VUMERITY | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 25.0 23.2 71.0 66.4
Interferon        
Disaggregation of Revenue [Line Items]        
Total revenue 246.9 237.5 719.9 732.0
Interferon | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 161.2 143.5 443.9 428.7
Interferon | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 85.7 94.0 276.0 303.3
AVONEX        
Disaggregation of Revenue [Line Items]        
Total revenue 188.5 176.2 533.0 537.5
AVONEX | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 133.4 115.6 363.7 344.0
AVONEX | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 55.1 60.6 169.3 193.5
PLEGRIDY        
Disaggregation of Revenue [Line Items]        
Total revenue 58.4 61.3 186.9 194.5
PLEGRIDY | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 27.8 27.9 80.2 84.7
PLEGRIDY | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 30.6 33.4 106.7 109.8
TYSABRI        
Disaggregation of Revenue [Line Items]        
Total revenue 431.8 406.1 1,267.9 1,299.6
TYSABRI | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 247.5 227.5 720.5 690.0
TYSABRI | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 184.3 178.6 547.4 609.6
FAMPYRA        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 19.4 0.3 57.3
FAMPYRA | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.0 0.0 0.0
FAMPYRA | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 19.4 0.3 57.3
Rare Disease Product Revenue        
Disaggregation of Revenue [Line Items]        
Total revenue 533.3 494.8 1,639.6 1,452.8
Rare Disease Product Revenue | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 235.1 240.4 700.9 703.8
Rare Disease Product Revenue | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 298.2 254.4 938.7 749.0
QALSODY        
Disaggregation of Revenue [Line Items]        
Total revenue 26.4 11.1 61.9 20.7
QALSODY | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 7.3 5.5 22.3 14.5
QALSODY | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 19.1 5.6 39.6 6.2
SPINRAZA        
Disaggregation of Revenue [Line Items]        
Total revenue 374.0 381.4 1,190.6 1,151.8
SPINRAZA | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 153.2 153.1 456.9 458.9
SPINRAZA | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 220.8 228.3 733.7 692.9
SKYCLARYS        
Disaggregation of Revenue [Line Items]        
Total revenue 132.9 102.3 387.1 280.3
SKYCLARYS | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 74.6 81.8 221.7 230.4
SKYCLARYS | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 58.3 20.5 165.4 49.9
Biosimilars        
Disaggregation of Revenue [Line Items]        
Total revenue 196.8 196.6 559.3 591.6
Biosimilars | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 2.0 4.3 8.8 19.1
Biosimilars | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 194.8 192.3 550.5 572.5
BENEPALI        
Disaggregation of Revenue [Line Items]        
Total revenue 121.9 118.1 345.3 354.1
BENEPALI | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.0 0.0 0.0
BENEPALI | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 121.9 118.1 345.3 354.1
IMRALDI        
Disaggregation of Revenue [Line Items]        
Total revenue 52.6 54.1 146.7 162.1
IMRALDI | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.0 0.0 0.0
IMRALDI | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 52.6 54.1 146.7 162.1
FLIXABI        
Disaggregation of Revenue [Line Items]        
Total revenue 15.3 16.2 42.7 47.1
FLIXABI | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.0 0.0 0.0
FLIXABI | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 15.3 16.2 42.7 47.1
BYOOVIZ        
Disaggregation of Revenue [Line Items]        
Total revenue 7.0 8.0 24.5 27.3
BYOOVIZ | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 2.0 4.1 8.7 18.1
BYOOVIZ | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 5.0 3.9 15.8 9.2
TOFIDENCE        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.2 0.1 1.0
TOFIDENCE | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.2 0.1 1.0
TOFIDENCE | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.0 0.0 0.0
Other        
Disaggregation of Revenue [Line Items]        
Total revenue 55.3 24.1 131.5 56.9
Other | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 55.3 22.3 129.8 51.3
Other | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 1.8 1.7 5.6
ZURZUVAE        
Disaggregation of Revenue [Line Items]        
Total revenue 55.3 22.0 129.4 49.3
ZURZUVAE | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 55.3 22.0 129.4 49.3
ZURZUVAE | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.0 0.0 0.0
FUMADERM And ADUHELM        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 2.1 2.1 7.6
FUMADERM And ADUHELM | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.3 0.4 2.0
FUMADERM And ADUHELM | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue $ 0.0 $ 1.8 $ 1.7 $ 5.6