Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Goodwill [Line Items]
Increase in goodwill			$ 540.9
Income tax expense (benefit)	$ 263.7	$ 269.6	586.2	$ 508.8
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period			4,632.5
Other			(3.1)
Goodwill, end of period	$ 5,170.3		5,170.3
TECFIDERA | Fumapharm AG
Goodwill [Line Items]
Increase in goodwill			600.0
Income tax expense (benefit)			$ 59.1