Summary of Significant Accounting Policies - Condensed Consolidated Statement of Operations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Apr. 02, 2016	Mar. 28, 2015	Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrued income taxes	$ 262.4		$ 62.7
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 (credits)	403.9	0.0
Restructuring	5.4	1.1
Total operating expenses	764.7	179.0
Operating income (loss)	(231.6)	190.4
Fair Value, Option, Changes in Fair Value, Gain (Loss)	(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)
Basic income (loss) per share (in dollars per share)	$ (3.70)	$ (0.16)
Diluted income (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
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrued income taxes	$ 179.4		85.2
Net sales	1,383.2	$ 1,049.1
Cost of sales	860.3	670.3
Gross profit	522.9	378.8
Operating expenses
Distribution	21.8	14.7
Research and development	45.3	35.4
Selling	180.8	48.8
Administration	106.4	79.6
Impairment charges (credits)	467.0	0.0
Restructuring	5.4	1.1
Total operating expenses	826.7	179.6
Operating income (loss)	(303.8)	199.2
Fair Value, Option, Changes in Fair Value, Gain (Loss)	0.0	0.0
Interest expense, net	51.2	43.3
Other expense, net	3.8	258.6
Loss on extinguishment of debt	0.4
Loss before income taxes	(359.2)	(102.7)
Income tax expense (benefit)	(24.6)	(7.8)
Net loss	$ (334.6)	$ (94.9)
Basic income (loss) per share (in dollars per share)	$ (2.34)	$ (0.67)
Diluted income (loss) per share (in dollars per share)	$ (2.34)	$ (0.67)
Weighted-average shares outstanding
Basic (in shares)	143.2	140.8
Diluted (in shares)	143.2	140.8
Adjustments | Tysabri®
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrued income taxes	$ 0.0		0.0
Net sales	(85.7)	$ (79.9)
Cost of sales	(72.5)	(72.5)
Gross profit	(13.2)	(7.4)
Operating expenses
Distribution	0.0	0.0
Research and development	0.0	0.0
Selling		0.0
Administration	0.0	0.0
Impairment charges (credits)	0.0	0.0
Restructuring	0.0	0.0
Total operating expenses	0.0	0.0
Operating income (loss)	(13.2)	(7.4)
Fair Value, Option, Changes in Fair Value, Gain (Loss)	(204.4)	100.8
Interest expense, net	0.0	0.0
Other expense, net	(0.1)	0.8
Loss on extinguishment of debt	0.0
Loss before income taxes	(217.5)	92.6
Income tax expense (benefit)	(27.2)	11.6
Net loss	$ (190.3)	$ 81.0
Basic income (loss) per share (in dollars per share)	$ (1.33)	$ 0.57
Diluted income (loss) per share (in dollars per share)	$ (1.33)	$ 0.57
Adjustments | Other
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrued income taxes	$ 83.0		$ (22.5)
Net sales	49.8	$ (2.0)
Cost of sales	26.4	0.0
Gross profit	23.4	(2.0)
Operating expenses
Distribution	0.0	0.0
Research and development	0.0	0.0
Selling	0.0	0.0
Administration	1.1	(0.6)
Impairment charges (credits)	(63.1)	0.0
Restructuring	0.0	0.0
Total operating expenses	(62.0)	(0.6)
Operating income (loss)	85.4	(1.4)
Fair Value, Option, Changes in Fair Value, Gain (Loss)	0.0	0.0
Interest expense, net	0.0	0.0
Other expense, net	(1.2)	(1.3)
Loss on extinguishment of debt	0.0
Loss before income taxes	86.6	(0.1)
Income tax expense (benefit)	90.9	8.2
Net loss	$ (4.3)	$ (8.3)
Basic income (loss) per share (in dollars per share)	$ (0.03)	$ (0.06)
Diluted income (loss) per share (in dollars per share)	$ (0.03)	$ (0.06)
Adjustments | BCH Deferred Tax Matters Misstatement
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrued income taxes	$ (29.6)
Operating expenses
Income tax expense (benefit)	(30.9)
Adjustments | BCH Belgium Distribution Contracts Misstatement
Operating expenses
Income tax expense (benefit)	6.9
Adjustments | Adjustments to Income Taxes Accounted For Under ASC 740
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrued income taxes	113.7
Operating expenses
Income tax expense (benefit)	$ 113.8