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Intangible Assets and Goodwill (Details 1) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Feb. 01, 2017
Goodwill [Line Items]
Increase to goodwill	$ 254.7
Income tax benefit (expense)	239.2	$ 356.4
Summary of roll forward of the changes in goodwill
Goodwill, beginning of period	3,669.3
Other	1.8
Goodwill, end of period	3,611.7
TECFIDERA \| Fumapharm AG
Goodwill [Line Items]
Increase to goodwill	300.0
Income tax benefit (expense)	45.3
Bioverativ
Goodwill [Line Items]
Elimination of goodwill allocated to our hemophilia business	$ (314.1)		$ (314.1)