v3.25.2
Revenues - Revenues by product (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 revenue $ 2,645.5 $ 2,464.9 $ 5,076.5 $ 4,755.4
Product revenue, net        
Disaggregation of Revenue [Line Items]        
Total revenue 1,878.7 1,899.6 3,605.2 3,611.5
Product revenue, net | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 941.1 846.7 1,694.9 1,592.8
Product revenue, net | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 937.6 1,052.9 1,910.3 2,018.7
MS Product Revenues        
Disaggregation of Revenue [Line Items]        
Total revenue 1,107.2 1,149.8 2,060.2 2,225.7
MS Product Revenues | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 657.4 582.4 1,147.8 1,085.6
MS Product Revenues | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 449.8 567.4 912.4 1,140.1
Fumarate        
Disaggregation of Revenue [Line Items]        
Total revenue 405.9 418.0 750.8 799.8
Fumarate | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 235.2 188.3 392.1 337.9
Fumarate | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 170.7 229.7 358.7 461.9
TECFIDERA        
Disaggregation of Revenue [Line Items]        
Total revenue 193.6 252.2 399.7 506.5
TECFIDERA | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 47.2 44.1 87.0 87.8
TECFIDERA | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 146.4 208.1 312.7 418.7
VUMERITY        
Disaggregation of Revenue [Line Items]        
Total revenue 212.3 165.8 351.1 293.3
VUMERITY | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 188.0 144.2 305.1 250.1
VUMERITY | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 24.3 21.6 46.0 43.2
Interferon        
Disaggregation of Revenue [Line Items]        
Total revenue 246.7 250.9 473.0 494.5
Interferon | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 150.0 145.4 282.7 285.2
Interferon | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 96.7 105.5 190.3 209.3
AVONEX        
Disaggregation of Revenue [Line Items]        
Total revenue 177.7 182.8 344.5 361.3
AVONEX | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 121.7 117.2 230.3 228.4
AVONEX | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 56.0 65.6 114.2 132.9
PLEGRIDY        
Disaggregation of Revenue [Line Items]        
Total revenue 69.0 68.1 128.5 133.2
PLEGRIDY | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 28.3 28.2 52.4 56.8
PLEGRIDY | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 40.7 39.9 76.1 76.4
TYSABRI        
Disaggregation of Revenue [Line Items]        
Total revenue 454.6 462.2 836.1 893.5
TYSABRI | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 272.2 248.7 473.0 462.5
TYSABRI | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 182.4 213.5 363.1 431.0
FAMPYRA        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 18.7 0.3 37.9
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 18.7 0.3 37.9
Rare Disease Product Revenue        
Disaggregation of Revenue [Line Items]        
Total revenue 543.0 534.1 1,106.3 958.0
Rare Disease Product Revenue | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 234.8 237.5 465.8 463.4
Rare Disease Product Revenue | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 308.2 296.6 640.5 494.6
QALSODY        
Disaggregation of Revenue [Line Items]        
Total revenue 20.0 5.0 35.5 9.6
QALSODY | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 7.5 4.6 15.0 9.0
QALSODY | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 12.5 0.4 20.5 0.6
SPINRAZA        
Disaggregation of Revenue [Line Items]        
Total revenue 392.7 429.1 816.6 770.4
SPINRAZA | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 149.3 157.3 303.7 305.8
SPINRAZA | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 243.4 271.8 512.9 464.6
SKYCLARYS        
Disaggregation of Revenue [Line Items]        
Total revenue 130.3 100.0 254.2 178.0
SKYCLARYS | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 78.0 75.6 147.1 148.6
SKYCLARYS | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 52.3 24.4 107.1 29.4
Biosimilars        
Disaggregation of Revenue [Line Items]        
Total revenue 181.7 198.1 362.5 395.0
Biosimilars | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 2.5 11.1 6.8 14.8
Biosimilars | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 179.2 187.0 355.7 380.2
BENEPALI        
Disaggregation of Revenue [Line Items]        
Total revenue 112.1 117.3 223.4 236.0
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 112.1 117.3 223.4 236.0
IMRALDI        
Disaggregation of Revenue [Line Items]        
Total revenue 46.7 53.2 94.1 108.0
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 46.7 53.2 94.1 108.0
FLIXABI        
Disaggregation of Revenue [Line Items]        
Total revenue 14.3 13.1 27.4 30.9
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 14.3 13.1 27.4 30.9
BYOOVIZ        
Disaggregation of Revenue [Line Items]        
Total revenue 8.6 13.7 17.5 19.3
BYOOVIZ | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 2.5 10.3 6.7 14.0
BYOOVIZ | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 6.1 3.4 10.8 5.3
TOFIDENCE        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.8 0.1 0.8
TOFIDENCE | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.8 0.1 0.8
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 46.8 17.6 76.2 32.8
Other | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 46.4 15.7 74.5 29.0
Other | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue 0.4 1.9 1.7 3.8
ZURZUVAE        
Disaggregation of Revenue [Line Items]        
Total revenue 46.4 14.9 74.1 27.3
ZURZUVAE | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 46.4 14.9 74.1 27.3
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 0.4 2.7 2.1 5.5
FUMADERM And ADUHELM | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 0.0 0.8 0.4 1.7
FUMADERM And ADUHELM | Rest of World        
Disaggregation of Revenue [Line Items]        
Total revenue $ 0.4 $ 1.9 $ 1.7 $ 3.8