Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Feb. 01, 2017
Goodwill [Line Items]
Increase to goodwill			$ 762.4
Income tax benefit (expense)	$ 383.8	$ 337.0	892.6	$ 1,047.0
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period			3,669.3
Other			9.9
Goodwill, end of period	$ 4,127.5		4,127.5
TECFIDERA | Fumapharm AG
Goodwill [Line Items]
Increase to goodwill			900.0
Income tax benefit (expense)			$ 137.6
Bioverativ
Goodwill [Line Items]
Elimination of goodwill allocated to our hemophilia business					$ (314.1)