Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 01, 2017
Goodwill [Line Items]
Income tax benefit (expense)	$ 1,425.6	$ 2,458.7	$ 1,237.3
Accumulated impairment losses related to goodwill	0.0
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period	4,632.5	3,669.3
Elimination of goodwill allocated to our hemophilia business	0.0			$ (314.1)
Increase to goodwill	1,080.1	1,267.3
Other	(6.2)	10.0
Goodwill, end of period	5,706.4	4,632.5	$ 3,669.3
Fumapharm AG | TECFIDERA
Goodwill [Line Items]
Income tax benefit (expense)	119.9	232.7
Summary of roll forward of the changes in goodwill
Increase to goodwill	1,200.0	$ 1,500.0
Bioverativ
Summary of roll forward of the changes in goodwill
Elimination of goodwill allocated to our hemophilia business				$ (314.1)
Each additional one billion up to twenty billion | Fumapharm AG | TECFIDERA
Goodwill [Line Items]
Cumulative sales level	$ 20,000.0