Consolidated Statements of Stockholders' Equity (USD $) In Millions, except Share data in Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in-Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]
Balance at Sep. 24, 2011	$ 2,936.8	$ 2.6	$ 5,303.7	$ (2,370.0)	$ 2.0	$ (1.5)
Balance (in shares) at Sep. 24, 2011		262,459				219
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	27.7		27.7
Exercise of stock options (in shares)		2,457
Issuance of common stock to employees upon vesting of restricted stock units, net of shares withheld for employee taxes	(5.7)		(5.7)
Issuance of common stock to employees upon vesting of restricted stock units, net of shares withheld for employee taxes (in shares)		673
Issuance of common stock under the employee stock purchase plan	0.9		0.9
Issuance of common shares under the employee stock purchase plan (in shares)		46
Stock-based compensation expense	40.0		40.0
Excess tax benefit from employee equity awards	4.4		4.4
Fair value of options exchanged in a business combination	2.7		2.7
Equity component related to convertible notes, net of taxes	23.0		23.0
Net income (loss)	(73.6)
Foreign currency translation adjustment	6.2				6.2
Adjustment to minimum pension liability, net	(1.5)				(1.5)
Unrealized losses on marketable securities	0.1				0.1
Balance at Sep. 29, 2012	2,961.0	2.6	5,396.7	(2,443.6)	6.8	(1.5)
Balance (in shares) at Sep. 29, 2012		265,635				219
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	65.7	0.1	65.6
Exercise of stock options (in shares)		4,786
Issuance of common stock to employees upon vesting of restricted stock units, net of shares withheld for employee taxes	(12.3)		(12.3)
Issuance of common stock to employees upon vesting of restricted stock units, net of shares withheld for employee taxes (in shares)		1,117
Issuance of common stock under the employee stock purchase plan	8.0		8.0
Issuance of common shares under the employee stock purchase plan (in shares)		498
Stock-based compensation expense	52.4		52.4
Excess tax benefit from employee equity awards	5.9		5.9
Equity component related to convertible notes, net of taxes	20.0		20.0
Net income (loss)	(1,172.8)
Foreign currency translation adjustment	1.4				1.4
Adjustment to minimum pension liability, net	0.1				0.1
Unrealized losses on marketable securities	12.1				12.1
Balance at Sep. 28, 2013	1,941.5	2.7	5,536.3	(3,616.4)	20.4	(1.5)
Balance (in shares) at Sep. 28, 2013		272,036				219
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	70.6	0.1	70.5
Exercise of stock options (in shares)	4,700	4,697
Issuance of common stock to employees upon vesting of restricted stock units, net of shares withheld for employee taxes	(9.8)		(9.8)
Issuance of common stock to employees upon vesting of restricted stock units, net of shares withheld for employee taxes (in shares)		846
Issuance of common stock under the employee stock purchase plan	10.9		10.9
Issuance of common shares under the employee stock purchase plan (in shares)		612
Stock-based compensation expense	49.5		49.5
Excess tax benefit from employee equity awards	0.8		0.8
Net income (loss)	17.3
Foreign currency translation adjustment	(13.3)				(13.3)
Adjustment to minimum pension liability, net	(1.3)				(1.3)
Retirement of treasury shares	0			(1.5)		1.5
Retirement of treasury shares (in shares)		(219)				(219)
Unrealized losses on marketable securities	(3.2)				(3.2)
Balance at Sep. 27, 2014	$ 2,063.0	$ 2.8	$ 5,658.2	$ (3,600.6)	$ 2.6	$ 0
Balance (in shares) at Sep. 27, 2014		277,972				0