Income Taxes - Activity of Company's Unrecognized Income Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 26, 2015	Sep. 27, 2014
Income Tax Disclosure [Abstract]
Balance at beginning of fiscal year	$ 137.0	$ 121.8
Tax positions related to current year:
Additions	11.0	10.8
Reductions	0.0	0.0
Tax positions related to prior years:
Additions related to change in estimate	21.1	10.9
Reductions	(10.3)	(2.7)
Payments	(0.8)	0.0
Lapses in statutes of limitations and settlements	(3.7)	(3.8)
Acquired tax positions:
Additions related to reserves acquired from acquisitions	0.4	0.0
Balance as of the end of the fiscal year	$ 154.7	$ 137.0