Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Line Items]
Income tax expense	$ 1,161.6	$ 989.9	$ 601.0
Accumulated impairment losses related to goodwill	0.0
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period	1,760.2	1,232.9
Increase to goodwill	908.1	527.3
Other goodwill adjustments	(4.5)	0.0
Goodwill, end of period	2,663.8	1,760.2	$ 1,232.9
Fumapharm AG | TECFIDERA
Goodwill [Line Items]
Income tax expense	120.2	72.7
Summary of roll forward of the changes in goodwill
Increase to goodwill	$ 900.0	$ 600.0