Quarterly Statement of Operations Information (Unaudited) - Summary of Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Sep. 24, 2016		Jun. 25, 2016		Mar. 26, 2016		Dec. 26, 2015		Sep. 26, 2015		Jun. 27, 2015		Mar. 28, 2015		Dec. 27, 2014		Sep. 24, 2016	Sep. 26, 2015	Sep. 27, 2014
Quarterly Financial Information Disclosure [Abstract]
Restructuring and divestiture charges	$ 2.9				$ 3.8		$ 2.3		$ 6.5		$ 11.9				$ 8.0		$ 10.5	$ 28.5	$ 51.7
Total revenues	726.8		$ 717.4		693.3		695.2		702.8		693.9		$ 655.5		652.8		2,832.7	2,705.0	2,530.7
Gross profit	406.1		393.1		385.0		379.1		379.4		378.7		336.0		338.6		1,563.3	1,432.7	1,245.5
Net income	$ 92.2	[1]	$ 84.8	[1]	$ 68.9	[1]	$ 84.9	[1]	$ 25.2	[2]	$ 29.4	[2]	$ 47.8	[2]	$ 29.2	[2]	$ 330.8	$ 131.6	$ 17.3
Diluted net income (loss) per common share (in dollars per share)	$ 0.33		$ 0.30		$ 0.24		$ 0.29		$ 0.09		$ 0.10		$ 0.17		$ 0.10		$ 1.16	$ 0.45	$ 0.06

[1] Net income in the first quarter of fiscal 2015 included restructuring charges of $8.0 million and a debt extinguishment loss of $6.7 million. Net income in the third quarter of fiscal 2015 included restructuring and divestiture charges of $11.9 million and a debt extinguishment loss of $18.2 million. Net income in the fourth quarter of fiscal 2015 included restructuring and divestiture charges of $6.5 million, a debt extinguishment loss of $37.8 million, and an other-than-temporary impairment charge of $7.8 million related to a marketable security.

[2] Net income in the first quarter of fiscal 2016 included restructuring charges of $2.3 million and a realized gain of $25.1 million related to the sale of all the shares in a marketable security investment. Net income in the second quarter of fiscal 2016 included restructuring charges of $3.8 million and a debt extinguishment loss of $4.5 million. Net income in the fourth quarter of fiscal 2016 included restructuring charges of $2.9 million, a debt extinguishment loss of $0.8 million, and an other-than-temporary impairment charge of $1.1 million related to a marketable security.