Income Taxes (Schedule of Reconciliation of Income Taxes at Statutory Rate and Tax Provision) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 27, 2019	Dec. 28, 2018	Dec. 29, 2017
Income Taxes [Line Items]
Income tax expense (benefit), intercompany financing and legal entity reorganization		$ (606.1)	$ (542.9)	$ (1,747.7)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		19.00%	19.00%	19.00%
Provision (benefit) for income taxes at U.K. statutory income tax rate (1)	[1]	$ (302.4)	$ (770.1)	$ 11.7
Adjustments to reconcile to income tax provision:
Rate difference between non-U.S. and U.S. jurisdictions	[2]	206.3	235.7	219.9
Goodwill, Impairment Loss			3,672.8
Valuation allowances, nonrecurring (3)	[3]	61.7	0.0	(3.7)
Adjustments to accrued income tax liabilities and uncertain tax positions		(12.4)	60.1	5.1
Interest and penalties on accrued income tax liabilities and uncertain tax positions		(6.3)	13.1	0.2
Credits, principally research	[4]	(13.5)	(25.9)	(13.8)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Amount		0.0	788.7	0.0
Permanently nondeductible and nontaxable items	[3]	98.1	7.2	6.4
Effective income tax rate reconciliation, pension plan settlement		0.0	0.0	(2.4)
Effective Income Tax Rate Reconciliation, Disposition of Business, Amount	[5]	9.6	(2.7)	18.2
Income tax benefit, tax cut and jobs act	[6]	0.0	(8.5)	(456.9)
Other		0.0	(0.3)	0.3
Income tax benefit, Legal Reorganization	[7]	(212.8)	(256.0)	(1,054.8)
Provision for (benefit from) income taxes		(584.3)	$ (430.1)	$ (1,709.6)
Intercompany Financing and Legal Entity Ownership Reorganization [Member]
Income Taxes [Line Items]
Income tax expense (benefit), intercompany financing and legal entity reorganization		$ (239.0)

[1] The statutory tax rate reflects the U.K. statutory tax rate of 19.0% for all periods presented.

[2] Includes the impact of certain recurring valuation allowances for U.K. and non-U.K. jurisdictions.

[3] During fiscal 2019 and 2018, the research and orphan drug credits decreased primarily as a result of the impact of the Tax Cut and Jobs Act of 2017 ("TCJA") and increased in conjunction with the Company's increased investment in qualified research, respectively.

[4] During fiscal 2019 and 2018, the research and orphan drug credits decreased primarily as a result of the impact of the Tax Cut and Jobs Act of 2017 ("TCJA") and increased in conjunction with the Company's increased investment in qualified research, respectively.

[5] The Company completed the sale of its wholly owned subsidiary BioVectra in November 2019, a portion of its Hemostasis business during fiscal 2018 and the Intrathecal Therapy Business during fiscal 2017.

[6] For fiscal 2018, the Company completed its analysis of the TCJA and recognized an additional tax benefit. Other line items, to the extent U.S. related, are reflected at the current U.S. statutory income tax rate of 21.0%. For fiscal 2017, the benefit reflects the redetermination of the Company's end of year net deferred tax liabilities as a result of the new U.S. statutory income tax rate of 21.0%. Other line items, to the extent U.S. related, are reflected at the former U.S. statutory income tax rate of 35.0%.

[7] Associated unrecognized tax benefit netted within this line.