Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock [Member]	Additional Paid-in-Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]
Balance (in shares) at Sep. 27, 2014		277,972				0
Balance at Sep. 27, 2014	$ 2,063.0	$ 2.8	$ 5,658.2	$ (3,600.6)	$ 2.6	$ 0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		3,036
Exercise of stock options	57.3	$ 0.0	57.3
Vesting of restricted stock units, net of shares withheld for employee taxes (in shares)		949
Vesting of restricted stock units, net of shares withheld for employee taxes	(12.9)		(12.9)
Common stock issued under the employee stock purchase plan (in shares)		538
Common stock issued under the employee stock purchase plan	12.0		12.0
Stock-based compensation expense	54.6		54.6
Excess tax benefit from equity awards	7.6		7.6
Reacquisition of equity component from convertible notes repurchase, net of taxes	(216.9)		(216.9)
Net income	131.6			131.6
Foreign currency translation adjustment	(20.6)				(20.6)
Amounts reclassified out of cumulative translation adjustment	9.6				9.6
Adjustment to minimum pension liability, net	(0.2)				(0.2)
Unrealized losses on derivatives, net of taxes	(3.9)				(3.9)
Other-than-temporary impairment of marketable security reclassified out of accumulated other comprehensive income (loss)	7.8				7.8
Unrealized losses on marketable securities	(9.8)				(9.8)
Interest cost of interest rate cap reclassified to statement of income	0.0
Net realized gains on marketable securities reclassified out of accumulated other comprehensive income (loss)	0.0
Balance (in shares) at Sep. 26, 2015		282,495				0
Balance at Sep. 26, 2015	2,079.2	$ 2.8	5,559.9	(3,469.0)	(14.5)	$ 0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		1,233
Exercise of stock options	24.1	$ 0.1	24.0
Vesting of restricted stock units, net of shares withheld for employee taxes (in shares)		820
Vesting of restricted stock units, net of shares withheld for employee taxes	(16.4)		(16.4)
Common stock issued under the employee stock purchase plan (in shares)		467
Common stock issued under the employee stock purchase plan	14.4		14.4
Stock-based compensation expense	62.3		62.3
Repurchase of common stock (in shares)						7,289
Repurchase of common stock	(250.0)					$ (250.0)
Excess tax benefit from equity awards	10.5		10.5
Reacquisition of equity component from convertible notes repurchase, net of taxes	(94.4)		(94.4)
Net income	330.8			330.8
Foreign currency translation adjustment	(10.4)				(10.4)
Adjustment to minimum pension liability, net	(0.7)				(0.7)
Unrealized losses on derivatives, net of taxes	(3.4)				(3.4)
Unrealized losses on marketable securities	(1.1)				(1.1)
Interest cost of interest rate cap reclassified to statement of income	3.9				3.9
Net realized gains on marketable securities reclassified out of accumulated other comprehensive income (loss)	(6.1)				(6.1)
Balance (in shares) at Sep. 24, 2016		285,015				7,289
Balance at Sep. 24, 2016	$ 2,142.7	$ 2.9	5,560.3	(3,138.2)	(32.3)	$ (250.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	1,400	1,427
Exercise of stock options	$ 33.1	$ 0.0	33.1
Vesting of restricted stock units, net of shares withheld for employee taxes (in shares)		939
Vesting of restricted stock units, net of shares withheld for employee taxes	(19.7)		(19.7)
Common stock issued under the employee stock purchase plan (in shares)		472
Common stock issued under the employee stock purchase plan	15.0		15.0
Stock-based compensation expense	68.2		68.2
Repurchase of common stock (in shares)						5,271
Repurchase of common stock	(200.1)					$ (200.1)
Reclassification of liability award to equity	7.8		7.8
Reacquisition of equity component from convertible notes repurchase, net of taxes	(33.9)		(33.9)
Net income	755.5			755.5
Foreign currency translation adjustment	7.6				7.6
Adjustment to minimum pension liability, net	0.9				0.9
Unrealized losses on derivatives, net of taxes	0.8				0.8
Unrealized losses on marketable securities	2.3				2.3
Interest cost of interest rate cap reclassified to statement of income	6.9				6.9
Net realized gains on marketable securities reclassified out of accumulated other comprehensive income (loss)	(2.4)				(2.4)
Balance (in shares) at Sep. 30, 2017		287,853				12,560
Balance at Sep. 30, 2017	$ 2,784.7	$ 2.9	$ 5,630.8	$ (2,382.7)	$ (16.2)	$ (450.1)