Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Income tax expense	$ 1,237.3	$ 1,161.6	$ 989.9
Accumulated impairment losses related to goodwill	0.0
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period	2,663.8	1,760.2
Increase to goodwill	1,026.9	908.1
Other goodwill adjustments	(21.4)	(4.5)
Goodwill, end of period	3,669.3	2,663.8	$ 1,760.2
Fumapharm AG | TECFIDERA
Goodwill [Line Items]
Income tax expense	173.1	120.2
Summary of roll forward of the changes in goodwill
Increase to goodwill	$ 1,200.0	$ 900.0