Income Taxes (Schedule of Reconciliation of Income Taxes at Statutory Rate and Tax Provision) (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended	12 Months Ended
		Dec. 30, 2016		Dec. 25, 2015	Sep. 26, 2014	Dec. 29, 2017		Sep. 30, 2016		Sep. 25, 2015
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		20.00%				19.00%		20.00%		20.00%
Provision (benefit) for income taxes at U.K. statutory income tax rate (1)	[1]	$ (59.7)				$ 11.7		$ 46.6		$ 21.4
Adjustments to reconcile to income tax provision:
Rate difference between non-U.S. and U.S. jurisdictions	[2]	(123.0)				(219.9)	[3]	(249.3)	[3]	(152.9)	[3]
Litigation Settlement, Expense		102.0
Valuation allowances, nonrecurring		0.0				(3.7)		2.1		(2.1)
Adjustments to accrued income tax liabilities and uncertain tax positions		0.9				5.1		(14.9)		(7.0)
Interest and penalties on accrued income tax liabilities and uncertain tax positions		(0.1)				(0.2)		16.4		(0.3)
Investment in partnership		(12.7)				0.0		0.0		0.0
Credits, principally research		(0.7)	[3],[4]		$ (3.6)	(13.8)	[3],[4]	(33.7)	[3],[4]	(8.1)	[3],[4]
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Amount		75.3				0.0		0.0		0.0
Permanently nondeductible and nontaxable items		1.6				6.4		7.9		14.7
Effective income tax rate reconciliation, pension plan settlement		0.0				(2.4)		0.0		0.0
Effective Income Tax Rate Reconciliation, Disposition of Business, Amount		0.0				18.2		0.0		0.0
Income tax benefit, tax cut and jobs act		0.0				(456.9)		0.0		0.0
Other		(3.3)				0.3		2.1		4.4
Income tax benefit, Legal Reorganization		0.0				(1,054.8)		0.0		0.0
Tax Adjustments, Settlements, and Unusual Provisions								27.4
Tax Benefit Resulting from Legal Settlement	[2]	16.1
Increase (Decrease) Deferred Tax Assets Resulting from Legal Settlements						37.5
Provision for (benefit from) income taxes		(121.7)		$ (37.3)		$ (1,709.6)		$ (255.6)		$ (129.3)
IRELAND
Income Taxes [Line Items]
Tax years that remain subject to examination						2013
Specialty Generics [Member]
Adjustments to reconcile to income tax provision:
Rate difference between non-U.S. and U.S. jurisdictions	[2]	34.5
Goodwill, Impairment Loss		$ 207.0

[1] The statutory tax rate reflects the U.K. statutory tax rate of 19% for fiscal 2017 and 20% for fiscal 2016, 2015 and the three months ended December 30, 2016.

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

[3] During fiscal 2015, the Research Credit tax law was extended, with a retroactive effective date of January 1, 2014. As such, fiscal 2015 includes approximately $3.6 million of credit related to the period January 1, 2014 through September 26, 2014.

[4] During fiscal 2016, the Company realized a tax benefit of $27.4 million resulting from a U.K. tax credit on a dividend between affiliates.