Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 29, 2018
OPERATING ACTIVITIES
Net income (loss)	$ 1,110,500,000	$ (203,600,000)	$ (111,300,000)
Adjustments to reconcile net income (loss) income to net cash provided by operating activities:
Depreciation	83,100,000	92,500,000	101,600,000
Amortization	292,900,000	370,600,000	378,700,000
Stock-based compensation expense	83,300,000	62,000,000.0	65,000,000.0
Deferred income taxes and other non-cash taxes	(94,400,000)	(235,700,000)	(477,300,000)
Goodwill impairment charge	0	0	685,700,000
Impairment of intangible assets and equipment	30,200,000	685,400,000	46,000,000.0
Debt extinguishment losses	0	800,000	45,900,000
Other adjustments and non-cash items	27,300,000	33,800,000	24,800,000
Changes in operating assets and liabilities, excluding the effect of acquisitions and dispositions:
Accounts receivable	(427,100,000)	(76,500,000)	(38,200,000)
Inventory	(25,300,000)	(63,000,000.0)	(50,600,000)
Prepaid income taxes	(3,800,000)	(3,200,000)	(9,400,000)
Prepaid expenses and other assets	(286,200,000)	(6,000,000.0)	(4,200,000)
Accounts payable	(4,900,000)	(5,500,000)	23,900,000
Accrued expenses and other liabilities	96,000,000.0	(16,500,000)	53,800,000
Deferred revenue	15,000,000.0	14,400,000	(1,500,000)
Net cash provided by operating activities	896,600,000	649,500,000	732,900,000
INVESTING ACTIVITIES
Acquisition of businesses, net of cash acquired	(119,400,000)	(110,600,000)	(76,500,000)
Net proceeds from sale of business	139,300,000	0	0
Payments to Acquire Equity Method Investments	0	(18,200,000)	0
Loans to SSI	0	(28,400,000)	0
Purchase of property and equipment	(98,300,000)	(57,000,000.0)	(58,400,000)
Increase in equipment under customer usage agreements	(58,100,000)	(52,100,000)	(47,200,000)
Purchase of cost method investment	0	(3,000,000.0)	(6,000,000.0)
Purchase of insurance contracts	(2,400,000)	0	0
Payments to Acquire in Process Research and Development	0	4,500,000	0
Other activity	(2,700,000)	(6,900,000)	(7,100,000)
Net cash (used in) provided by investing activities	(141,600,000)	(280,700,000)	(195,200,000)
FINANCING ACTIVITIES
Proceeds from long-term debt	0	1,500,000,000.0	1,500,000,000.0
Repayment of long-term debt	(37,500,000)	(1,462,500,000)	(1,359,400,000)
Proceeds from Senior Notes	0	0	1,350,000,000.0
Repayment of Senior Notes	0	0	(1,037,700,000)
Payments to extinguish convertible notes	0	0	(546,200,000)
Repayment of acquired debt	(8,300,000)	(2,500,000)	(3,300,000)
Proceeds from revolving credit line	750,000,000.0	480,000,000.0	1,150,000,000.0
Repayments under revolving credit line	(500,000,000.0)	(780,000,000.0)	(1,195,000,000.0)
Proceeds from accounts receivable securitization agreement	16,000,000.0	43,000,000.0	34,000,000.0
Repayments under accounts receivable securitization agreement	(250,000,000.0)	(34,000,000.0)	(9,000,000.0)
Payments to Noncontrolling Interests	(1,800,000)	0	0
Repurchases of common stock	(653,600,000)	(200,100,000)	(275,800,000)
Payment of debt issuance costs	0	(2,700,000)	(23,500,000)
Payment for Contingent Consideration Liability, Financing Activities	(24,300,000)	(6,500,000)	0
Purchase of interest rate caps	0	(1,500,000)	(3,700,000)
Net proceeds from issuance of common stock under employee stock plans	65,600,000	49,800,000	33,200,000
Payments under finance lease obligations	(1,700,000)	(1,700,000)	(1,700,000)
Payment of minimum tax withholdings on net share settlements of equity awards	(14,300,000)	(12,800,000)	(16,700,000)
Net cash used in financing activities	(659,900,000)	(431,500,000)	(404,800,000)
Effect of exchange rate changes on cash and cash equivalents	4,100,000	(2,200,000)	(6,800,000)
Net increase (decrease) in cash and cash equivalents	99,200,000	(64,900,000)	126,100,000
Cash and cash equivalents, beginning of period	601,800,000	666,700,000	540,600,000
Cash and cash equivalents, end of period	$ 701,000,000.0	$ 601,800,000	$ 666,700,000