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Segment Information (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net | $ 2,712.4 | $ 2,622.5 | $ 2,639.7 | $ 2,380.1 | $ 2,502.9 | $ 2,539.6 | $ 2,466.0 | $ 2,309.4 | $ 10,354.7 | $ 9,817.9 | $ 9,188.5
U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 7,017.1 | 7,050.4 | 6,545.8
Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 3,337.6 | 2,767.5 | 2,642.7
TECFIDERA |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 4,214.0 | 3,968.1 | 3,638.4
TECFIDERA | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 3,294.0 | 3,169.4 | 2,908.2
TECFIDERA | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 920.0 | 798.7 | 730.2
AVONEX |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 2,151.5 | 2,313.5 | 2,630.2
AVONEX | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 1,593.6 | 1,675.3 | 1,790.2
AVONEX | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 557.9 | 638.2 | 840.0
PLEGRIDY |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 494.3 | 481.7 | 338.5
PLEGRIDY | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 295.5 | 305.0 | 227.1
PLEGRIDY | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 198.8 | 176.7 | 111.4
TYSABRI |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 1,973.1 | 1,963.8 | 1,886.1
TYSABRI | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 1,113.8 | 1,182.9 | 1,103.1
TYSABRI | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 859.3 | 780.9 | 783.0
FAMPYRA |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 91.6 | 84.9 | 89.7
FAMPYRA | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
FAMPYRA | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 91.6 | 84.9 | 89.7
ZINBRYTA |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 52.7 | 7.8 | 0.0
ZINBRYTA | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
ZINBRYTA | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 52.7 | 7.8 | 0.0
SPINRAZA |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 883.7 | 4.6 | 0.0
SPINRAZA | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 657.0 | 4.6 | 0.0
SPINRAZA | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 226.7 | 0.0 | 0.0
ELOCTATE |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 48.4 | 513.2 | 319.7
ELOCTATE | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 42.2 | 445.2 | 308.3
ELOCTATE | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 6.2 | 68.0 | 11.4
ALPROLIX |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 26.0 | 333.7 | 234.5
ALPROLIX | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 21.0 | 268.0 | 208.9
ALPROLIX | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 5.0 | 65.7 | 25.6
FUMADERM |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 39.6 | 45.9 | 51.4
FUMADERM | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
FUMADERM | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 39.6 | 45.9 | 51.4
BENEPALI |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 370.8 | 100.6 | 0.0
BENEPALI | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
BENEPALI | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 370.8 | 100.6 | 0.0
FLIXABI |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 9.0 | 0.1 | 0.0
FLIXABI | U.S |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | 0.0 | 0.0 | 0.0
FLIXABI | Rest of world |  |  |  |  |  |  |  |  |  |  |
Revenue by product |  |  |  |  |  |  |  |  |  |  |
Product, net |  |  |  |  |  |  |  |  | $ 9.0 | $ 0.1 | $ 0.0

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