Condensed Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Apr. 02, 2016	Mar. 28, 2015
Income Statement [Abstract]
Net sales	$ 1,347.3	$ 967.2
Cost of sales	814.2	597.8
Gross profit	533.1	369.4
Operating expenses
Distribution	21.8	14.7
Research and development	45.3	35.4
Selling	180.8	48.8
Administration	107.5	79.0
Impairment charges	403.9	0.0
Restructuring	5.4	1.1
Total operating expenses	764.7	179.0
Operating income (loss)	(231.6)	190.4
Tysabri® royalty stream - change in fair value	204.4	(100.8)
Interest expense, net	51.2	43.3
Other expense, net	2.5	258.1
Loss on extinguishment of debt	0.4	0.0
Loss before income taxes	(490.1)	(10.2)
Income tax expense (benefit)	39.1	12.0
Net loss	$ (529.2)	$ (22.2)
Loss per share
Basic loss per share (in dollars per share)	$ (3.70)	$ (0.16)
Diluted loss per share (in dollars per share)	$ (3.70)	$ (0.16)
Weighted-average shares outstanding
Basic (in shares)	143.2	140.8
Diluted (in shares)	143.2	140.8
Dividends declared per share (in dollars per share)	$ 0.145	$ 0.125