Summary of Significant Accounting Policies - Condensed Consolidated Statement of Operations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended			6 Months Ended
	Jul. 02, 2016	Jun. 27, 2015	Mar. 28, 2015	Jul. 02, 2016		Jun. 27, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net sales	$ 1,340.5	$ 1,415.2		$ 2,687.8	[1]	$ 2,382.4	[1]
Cost of sales	794.0	814.2		1,608.2		1,412.0
Gross profit	546.5	601.0		1,079.6		970.4
Operating expenses
Distribution	22.5	23.7		44.3		38.4
Research and development	47.0	62.6		92.2		98.0
Selling	171.6	174.9		352.4		223.7
Administration	104.3	140.8		211.8		219.8
Impairment charges	10.5	6.8		414.4		6.8
Restructuring	5.8	(0.1)		11.3		1.0
Total operating expenses	361.7	408.7		1,126.4		587.7
Operating income	184.8	192.3		(46.8)	[1]	382.7	[1]
Tysabri® royalty stream - change in fair value	910.8	69.2		1,115.3		(31.5)
Interest expense, net	57.4	45.9		108.6		89.2
Other expense, net	28.8	15.8		31.3		273.9
Loss on extinguishment of debt	0.0	0.9		0.4		0.9
Income (loss) before income taxes	(812.2)	60.5		(1,302.4)		50.2
Income tax expense (benefit)	277.9	(82.7)		238.9		(94.7)
Net loss	$ (534.3)	$ (22.2)		$ (1,063.5)		$ (44.5)
Loss per share
Basic income (loss) per share (in dollars per share)	$ (3.73)	$ (0.15)		$ (7.43)		$ (0.31)
Diluted income (loss) per share (in dollars per share)	$ (3.73)	$ (0.15)		$ (7.43)		$ (0.31)
Weighted-average shares outstanding
Basic (in shares)	143.2	146.3		143.2		143.5
Diluted (in shares)	143.2	146.3		143.2		143.5
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net sales	$ 1,481.0	$ 1,531.6		$ 2,864.2		$ 2,580.8
Cost of sales	913.8	903.5		1,774.1		1,573.8
Gross profit	567.2	628.1		1,090.1		1,007.0
Operating expenses
Distribution	22.5	23.7		44.3		38.4
Research and development	47.0	62.6		92.2		98.0
Selling	171.6	174.9		352.4		223.7
Administration	101.8	140.1		208.2		219.7
Impairment charges	(19.8)	0.0	$ 0.0	447.2		0.0
Restructuring	5.8	(0.1)		11.3		1.0
Total operating expenses	328.9	401.2		1,155.6		580.8
Operating income	238.3	226.9		(65.5)		426.2
Tysabri® royalty stream - change in fair value	0.0	0.0		0.0		0.0
Interest expense, net	57.4	45.9		108.6		89.2
Other expense, net	29.3	22.7		33.1		281.3
Loss on extinguishment of debt		0.9		0.4		0.9
Income (loss) before income taxes	151.6	157.4		(207.6)		54.8
Income tax expense (benefit)	42.7	(101.0)		67.3		(93.2)
Net loss	$ 194.3	$ 56.4		$ (140.3)		$ (38.4)
Loss per share
Basic income (loss) per share (in dollars per share)	$ 1.36	$ 0.39		$ (0.98)		$ (0.27)
Diluted income (loss) per share (in dollars per share)	$ 1.35	$ 0.38		$ (0.98)		$ (0.27)
Weighted-average shares outstanding
Basic (in shares)	143.2	146.3		143.2		143.5
Diluted (in shares)	143.2	146.8		143.6		143.5
Tysabri® | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net sales	$ (88.9)	$ (81.6)		$ (174.6)		$ (161.6)
Cost of sales	(72.5)	(72.5)		(145.0)		(145.1)
Gross profit	(16.4)	(9.1)		(29.6)		(16.5)
Operating expenses
Distribution	0.0	0.0		0.0		0.0
Research and development	0.0	0.0		0.0		0.0
Selling	0.0	0.0		0.0		0.0
Administration	0.0	0.0		0.0		0.0
Impairment charges	0.0	0.0	0.0	0.0		0.0
Restructuring	0.0	0.0		0.0		0.0
Total operating expenses	0.0	0.0		0.0		0.0
Operating income	(16.4)	(9.1)		(29.6)		(16.5)
Tysabri® royalty stream - change in fair value	910.8	69.2		1,115.3		(31.5)
Interest expense, net	0.0	0.0		0.0		0.0
Other expense, net	0.2	(0.8)		0.1		0.0
Loss on extinguishment of debt		0.0		0.0		0.0
Income (loss) before income taxes	(927.4)	(77.5)		(1,145.0)		15.0
Income tax expense (benefit)	116.0	9.7		143.2		(1.9)
Net loss	$ (811.4)	$ (67.8)		$ (1,001.8)		$ 13.1
Loss per share
Basic income (loss) per share (in dollars per share)	$ (5.67)	$ (0.46)		$ (6.99)		$ 0.09
Diluted income (loss) per share (in dollars per share)	$ (5.67)	$ (0.46)		$ (6.99)		$ 0.09
Other | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net sales	$ (51.6)	$ (34.8)		$ (1.8)		$ (36.8)
Cost of sales	(47.3)	(16.8)		(20.9)		(16.7)
Gross profit	(4.3)	(18.0)		19.1		(20.1)
Operating expenses
Distribution	0.0	0.0		0.0		0.0
Research and development	0.0	0.0		0.0		0.0
Selling	0.0	0.0		0.0		0.0
Administration	2.5	0.7		3.6		0.1
Impairment charges	30.3	6.8	$ 6.8	(32.8)		6.8
Restructuring	0.0	0.0		0.0		0.0
Total operating expenses	32.8	7.5		(29.2)		6.9
Operating income	(37.1)	(25.5)		48.3		(27.0)
Tysabri® royalty stream - change in fair value	0.0	0.0		0.0		0.0
Interest expense, net	0.0	0.0		0.0		0.0
Other expense, net	(0.7)	(6.1)		(1.9)		(7.4)
Loss on extinguishment of debt		0.0		0.0		0.0
Income (loss) before income taxes	(36.4)	(19.4)		50.2		(19.6)
Income tax expense (benefit)	119.2	8.6		28.4		0.4
Net loss	$ 82.8	$ (10.8)		$ 78.6		$ (19.2)
Loss per share
Basic income (loss) per share (in dollars per share)	$ 0.58	$ (0.08)		$ 0.54		$ (0.13)
Diluted income (loss) per share (in dollars per share)	$ 0.58	$ (0.07)		$ 0.54		$ (0.13)
BCH Deferred Tax Matters Misstatement | Adjustments
Operating expenses
Income tax expense (benefit)	$ (4.5)	$ (6.5)		$ 26.4
BCH Belgium Distribution Contracts Misstatement | Adjustments
Operating expenses
Income tax expense (benefit)	3.4	$ 3.3		(3.5)
Adjustments to Income Taxes Accounted For Under ASC 740 | Adjustments
Operating expenses
Income tax expense (benefit)	$ 121.8			$ 8.0

[1] The BCH segment was created on March 30, 2015 as a result of the Omega acquisition, thus data for the six months ended June 27, 2015 includes only three months of results from operations attributable to Omega.