Reconciliation for Assets and Liabilities Measured and Recorded at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 26, 2014
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 62.7
Additions	51.0	[1]
Sale of portion of corporate debt security	(38.1)	[2]
Ending balance	75.6
Option to Purchase a Privately-Held Company
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	1.4
Change in fair value recognized in earnings	(1.4)
Contingent Consideration
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	(2.5)
Additions	6.2	[1]
Settlements	0.5	[3]
Change in fair value recognized in earnings	0.7
Ending balance	$ (7.5)

[1] Amounts reported under Available-For-Sale Corporate Debt Securities include accrued interest.

[2] Refer to Note 16 “CPTC Loans”

[3] Amounts reported under “Contingent Consideration” represent cash payments to settle contingent consideration liabilities.