Summary of Significant Accounting Policies - Condensed Consolidated Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 02, 2016	Mar. 28, 2015
Cash Flows From (For) Operating Activities
Net loss	$ (529.2)	$ (22.2)
Adjustments to derive cash flows
Loss on extinguishment of debt	0.4	0.0
Restructuring charges	5.4	1.1
Depreciation and amortization	109.7	55.1
Impairment charges	403.9	0.0
Tysabri® royalty stream - change in fair value	204.4	(100.8)
Share-based compensation	15.8	7.5
Loss on acquisition-related foreign currency derivatives	0.0	298.1
Amortization of financing fees and debt discount (premium)	(6.7)	1.8
Deferred income taxes	(178.3)	(34.7)
Other non-cash adjustments	1.6	(0.1)
Subtotal	27.0	205.8
Increase (decrease) in cash due to:
Accounts receivable	17.3	32.3
Inventories	4.4	2.1
Accounts payable	(3.2)	18.0
Payroll and related taxes	(37.4)	(1.0)
Accrued customer programs	(81.7)	(27.8)
Accrued liabilities	(12.8)	(2.5)
Accrued income taxes	185.7	(42.9)
Other	(0.8)	(3.8)
Subtotal	71.5	(25.6)
Net cash from (for) operating activities	98.5	180.2
Cash Flows From (For) Investing Activities
Proceeds from royalty rights	83.4	87.8
Acquisitions of businesses, net of cash acquired	(416.4)	(4.0)
Settlement of acquisition-related foreign currency derivatives	0.0	(298.1)
Additions to property, plant and equipment	(34.7)	(31.9)
Other investing	(1.0)	0.0
Net cash from (for) investing activities	(368.7)	(246.2)
Cash Flows From (For) Financing Activities
Issuances of long-term debt	1,190.3	0.0
Borrowings (repayments) of revolving credit agreements and other financing, net	(715.9)	3.4
Payments on long-term debt	(14.3)	(13.6)
Deferred financing fees	(1.5)	(3.3)
Issuance of ordinary shares	3.1	1.2
Repurchase of ordinary shares	0.0	(0.1)
Cash dividends	(20.8)	(17.6)
Other financing	(3.5)	(1.6)
Net cash from (for) financing activities	437.4	(31.6)
Effect of exchange rate changes on cash and cash equivalents	3.9	(68.1)
Net increase (decrease) in cash and cash equivalents	171.1	(165.7)
Cash and cash equivalents, beginning of period	417.8	3,596.1
Cash and cash equivalents, end of period	588.9	3,430.4
Previously Reported
Cash Flows From (For) Operating Activities
Net loss	(334.6)	(94.9)
Adjustments to derive cash flows
Loss on extinguishment of debt	0.4
Restructuring charges	5.4	1.1
Depreciation and amortization	182.5	127.7
Impairment charges	467.0	0.0
Tysabri® royalty stream - change in fair value	0.0	0.0
Share-based compensation	13.8	7.5
Loss on acquisition-related foreign currency derivatives		298.1
Amortization of financing fees and debt discount (premium)	0.0	0.0
Deferred income taxes	(138.0)	(46.3)
Other non-cash adjustments	1.6	(0.2)
Subtotal	198.1	293.0
Increase (decrease) in cash due to:
Accounts receivable	23.0	39.4
Inventories	(14.8)	2.1
Accounts payable	0.3	18.0
Payroll and related taxes	(37.4)	(1.0)
Accrued customer programs	(69.7)	(27.8)
Accrued liabilities	(3.4)	(2.5)
Accrued income taxes	99.5	(51.2)
Other	(25.3)	(2.0)
Subtotal	(27.8)	(25.0)
Net cash from (for) operating activities	170.3	268.0
Cash Flows From (For) Investing Activities
Proceeds from royalty rights	0.0	0.0
Acquisitions of businesses, net of cash acquired	(416.4)	(4.0)
Settlement of acquisition-related foreign currency derivatives		(298.1)
Additions to property, plant and equipment	(34.7)	(31.9)
Other investing	(1.0)
Net cash from (for) investing activities	(452.1)	(334.0)
Cash Flows From (For) Financing Activities
Issuances of long-term debt	1,190.3
Borrowings (repayments) of revolving credit agreements and other financing, net	(704.3)	3.4
Payments on long-term debt	(14.3)	(13.6)
Deferred financing fees	(1.5)	(3.3)
Issuance of ordinary shares	3.1	1.2
Repurchase of ordinary shares		(0.1)
Cash dividends	(20.8)	(17.6)
Other financing	(3.5)	(1.6)
Net cash from (for) financing activities	449.0	(31.6)
Effect of exchange rate changes on cash and cash equivalents	3.9	(68.1)
Net increase (decrease) in cash and cash equivalents	171.1	(165.7)
Cash and cash equivalents, beginning of period	417.8	3,596.1
Cash and cash equivalents, end of period	588.9	3,430.4
Adjustments | Tysabri®
Cash Flows From (For) Operating Activities
Net loss	(190.3)	81.0
Adjustments to derive cash flows
Loss on extinguishment of debt	0.0
Restructuring charges	0.0	0.0
Depreciation and amortization	(72.5)	(72.6)
Impairment charges	0.0	0.0
Tysabri® royalty stream - change in fair value	204.4	(100.8)
Share-based compensation	0.0	0.0
Loss on acquisition-related foreign currency derivatives		0.0
Amortization of financing fees and debt discount (premium)	0.0	0.0
Deferred income taxes	(27.2)	11.6
Other non-cash adjustments	0.0	0.1
Subtotal	(85.6)	(80.7)
Increase (decrease) in cash due to:
Accounts receivable	2.2	(5.9)
Inventories	0.0	0.0
Accounts payable	0.0	0.0
Payroll and related taxes	0.0	0.0
Accrued customer programs	0.0	0.0
Accrued liabilities	0.0	0.0
Accrued income taxes	0.0	0.0
Other	0.0	0.0
Subtotal	2.2	(5.9)
Net cash from (for) operating activities	(83.4)	(86.6)
Cash Flows From (For) Investing Activities
Proceeds from royalty rights	83.4	86.6
Acquisitions of businesses, net of cash acquired	0.0	0.0
Settlement of acquisition-related foreign currency derivatives		0.0
Additions to property, plant and equipment	0.0	0.0
Other investing	0.0
Net cash from (for) investing activities	83.4	86.6
Cash Flows From (For) Financing Activities
Issuances of long-term debt	0.0
Borrowings (repayments) of revolving credit agreements and other financing, net	0.0	0.0
Payments on long-term debt	0.0	0.0
Deferred financing fees	0.0	0.0
Issuance of ordinary shares	0.0	0.0
Repurchase of ordinary shares		0.0
Cash dividends	0.0	0.0
Other financing	0.0	0.0
Net cash from (for) financing activities	0.0	0.0
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0
Net increase (decrease) in cash and cash equivalents	0.0	0.0
Cash and cash equivalents, beginning of period	0.0	0.0
Cash and cash equivalents, end of period	0.0	0.0
Adjustments | Other
Cash Flows From (For) Operating Activities
Net loss	(4.3)	(8.3)
Adjustments to derive cash flows
Loss on extinguishment of debt	0.0
Restructuring charges	0.0	0.0
Depreciation and amortization	(0.3)	0.0
Impairment charges	(63.1)	0.0
Tysabri® royalty stream - change in fair value	0.0	0.0
Share-based compensation	2.0	0.0
Loss on acquisition-related foreign currency derivatives		0.0
Amortization of financing fees and debt discount (premium)	(6.7)	1.8
Deferred income taxes	(13.1)	0.0
Other non-cash adjustments	0.0	0.0
Subtotal	(85.5)	(6.5)
Increase (decrease) in cash due to:
Accounts receivable	(7.9)	(1.2)
Inventories	19.2	0.0
Accounts payable	(3.5)	0.0
Payroll and related taxes	0.0	0.0
Accrued customer programs	(12.0)	0.0
Accrued liabilities	(9.4)	0.0
Accrued income taxes	86.2	8.3
Other	24.5	(1.8)
Subtotal	97.1	5.3
Net cash from (for) operating activities	11.6	(1.2)
Cash Flows From (For) Investing Activities
Proceeds from royalty rights	0.0	1.2
Acquisitions of businesses, net of cash acquired	0.0	0.0
Settlement of acquisition-related foreign currency derivatives		0.0
Additions to property, plant and equipment	0.0	0.0
Other investing	0.0
Net cash from (for) investing activities	0.0	1.2
Cash Flows From (For) Financing Activities
Issuances of long-term debt	0.0
Borrowings (repayments) of revolving credit agreements and other financing, net	(11.6)	0.0
Payments on long-term debt	0.0	0.0
Deferred financing fees	0.0	0.0
Issuance of ordinary shares	0.0	0.0
Cash dividends	0.0	0.0
Other financing	0.0	0.0
Net cash from (for) financing activities	(11.6)	0.0
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0
Net increase (decrease) in cash and cash equivalents	0.0	0.0
Cash and cash equivalents, beginning of period	0.0	0.0
Cash and cash equivalents, end of period	$ 0.0	$ 0.0