Hologic (HOLX) 10-K 21 Nov 17 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2017	Nov. 14, 2017	Apr. 01, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Entity Registrant Name	HOLOGIC INC
Entity Central Index Key	859,737
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		275,683,548
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 11,852,439,894

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Revenues:
Product	$ 2,538	$ 2,379	$ 2,270.4
Service and other	520.8	453.7	434.6
Revenues	3,058.8	2,832.7	2,705
Costs of revenues:
Product	881.8	756.8	755.5
Amortization of intangible assets	297.1	293.4	299.7
Service and other	258.9	219.2	217.1
Gross Profit	1,621	1,563.3	1,432.7
Operating expenses:
Research and development	232.8	232.1	214.9
Selling and marketing	498.6	415.1	363
General and administrative	343.3	267.3	261
Amortization of intangible assets	62.5	89.7	110.2
Gain on sale of business	(899.7)	0	0
Restructuring and divestiture charges	13.3	10.5	28.5
Operating expenses	250.8	1,014.7	977.6
Income from operations	1,370.2	548.6	455.1
Interest income	3.8	0.7	1.3
Interest expense	(153.2)	(155.3)	(205.5)
Debt extinguishment losses	(3.2)	(5.3)	(62.7)
Other income (expense), net	12.9	26.6	(11)
Income before income taxes	1,230.5	415.3	177.2
Provision for income taxes	475	84.5	45.6
Net income	$ 755.5	$ 330.8	$ 131.6
Net income per common share:
Basic (in dollars per share)	$ 2.70	$ 1.18	$ 0.47
Diluted (in dollars per share)	$ 2.64	$ 1.16	$ 0.45
Weighted average number of shares outstanding:
Basic (in shares)	279,811	280,213	280,566
Diluted (in shares)	285,653	286,156	289,537

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 755.5	$ 330.8	$ 131.6
Changes in foreign currency translation adjustment	7.6	(10.4)	(11)
Loss recognized in accumulated other comprehensive income (loss)	2.3	(1.1)	(2)
Net (gains) losses reclassified from accumulated other comprehensive income to the statement of income	(2.4)	(6.1)	0
Changes in pension plans, net of taxes of $1.1 in 2017, $0.3 in 2016, and $0.3 in 2015	0.9	(0.7)	(0.2)
Loss recognized in other comprehensive income, net	0.8	(3.4)	(3.9)
Loss reclassified from accumulated other comprehensive income to the statement of operations, net	6.9	3.9	0
Other comprehensive income (loss)	16.1	(17.8)	(17.1)
Comprehensive income	$ 771.6	$ 313	$ 114.5

Consolidated Statements of Com4

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Statement of Comprehensive Income [Abstract]
Changes in unrealized holding gains and losses on available-for-sale securities, tax	$ 0.1
Changes in pension plans, taxes	1.1	$ 0.3	$ 0.3
Changes in value of hedged interest rate caps, tax	$ 0.6	$ 2	$ 2.5

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Current assets:
Cash and cash equivalents	$ 540.6	$ 548.4
Accounts receivable, less reserves of $9.8 and $12.7, respectively	533.5	447
Inventories	331.6	274.7
Prepaid income taxes	22.4	16.9
Prepaid expenses and other current assets	50.5	39.6
Total current assets	1,478.6	1,326.6
Property, plant and equipment, net	491.2	460.2
Intangible assets, net	2,741.6	2,643.4
Goodwill	3,171.2	2,803.1
Other assets	97	83.7
Total assets	7,979.6	7,317
Current liabilities:
Current portion of long-term debt	1,150.8	296
Accounts payable	166.6	156.9
Accrued expenses	375.3	287.6
Deferred revenue	171.2	161.4
Current portion of capital lease obligations	1.6	0
Total current liabilities	1,865.5	901.9
Long-term debt, net of current portion	2,172.1	3,049.4
Capital lease obligations, net of current portion	22.7	0
Deferred income tax liabilities	973.6	982.6
Deferred revenue	20.8	15.9
Other long-term liabilities	140.2	224.5
Commitments and contingencies (Note 11)
Stockholders’ equity:
Preferred stock, $0.01 par value – 1,623 shares authorized; 0 shares issued	0	0
Common stock, $0.01 par value – 750,000 shares authorized; 287,853 and 285,015 shares issued, respectively	2.9	2.9
Additional paid-in-capital	5,630.8	5,560.3
Accumulated deficit	(2,382.7)	(3,138.2)
Treasury stock, at cost – 12,560 and 7,289 shares, respectively	(450.1)	(250)
Accumulated other comprehensive loss	(16.2)	(32.3)
Total stockholders’ equity	2,784.7	2,142.7
Total liabilities and stockholders’ equity	$ 7,979.6	$ 7,317

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Statement of Financial Position [Abstract]
Accounts receivable, reserves	$ 9.8	$ 12.7
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	1,623,000	1,623,000
Preferred stock, shares issued	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	750,000,000	750,000,000
Common stock, shares issued	287,853,000	285,015,000
Treasury stock, shares	12,560,000	7,289,000

Consolidated Statements of Stoc

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	$ 2.8	$ 5,658.2	$ (3,600.6)	$ 2.6	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		3,036
Exercise of stock options	57.3	$ 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		12
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
Net realized gains on marketable securities reclassified out of accumulated other comprehensive income (loss)	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)	(14.5)	$ 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
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)					$ (250)
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	1,400	1,427
Exercise of stock options	$ 33.1	$ 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		15
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)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
OPERATING ACTIVITIES
Net income	$ 755.5	$ 330.8	$ 131.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	89.6	82.3	81.5
Amortization	359.6	383.1	409.9
Non-cash interest expense	49.4	52.1	63.8
Stock-based compensation expense	68.2	65.4	59.3
Deferred income taxes and other non-cash taxes	(357.2)	(155.8)	(148.8)
Gain on sale of investments	(5.6)	(25.1)	0
Fair value write-up of inventory sold	39.7	0	0
Debt extinguishment losses	3.2	5.3	62.7
Equity investment impairment charges	0	1.1	7.8
(Gain) loss on sale of businesses	(899.7)	0	9.6
Other adjustments and non-cash items	8.8	2.6	20.9
Changes in operating assets and liabilities, excluding the effect of acquisitions and dispositions:
Accounts receivable	(41.5)	(31.8)	(30.3)
Inventories	(11.6)	7.6	43.9
Prepaid income taxes	(8.7)	4.7	0.7
Prepaid expenses and other assets	(2.4)	(4.9)	5.7
Accounts payable	(10.6)	40.1	25.5
Accrued expenses and other liabilities	(17.8)	45.6	36.9
Deferred revenue	(10.6)	(4.9)	16.1
Net cash provided by operating activities	8.3	798.2	796.8
INVESTING ACTIVITIES
Acquisition of businesses, net of cash acquired	(1,558.1)	0	0
Proceeds from sale of business	1,865	0	0
Purchase of property and equipment	(57.8)	(47.3)	(48.1)
Increase in equipment under customer usage agreements	(49.8)	(47.2)	(41.3)
Proceeds from sale of available-for-sale marketable securities	87.1	31.1	0
Purchases of insurance contracts	0	(5.2)	(6.4)
Sales of mutual funds	0	5.2	10
Purchase of intellectual property	0	(4)	0
Other activity	(0.6)	(1)	(0.3)
Net cash provided by (used in) investing activities	285.8	(68.4)	(86.1)
FINANCING ACTIVITIES
Proceeds from long-term debt	0	0	2,495.1
Repayment of long-term debt	(84.4)	(75)	(3,095)
Payments to extinguish convertible notes	(396.2)	(392.8)	(543.7)
Proceeds from amounts borrowed under revolving credit line	345	50	358
Repayment of amounts borrowed under revolving credit line	0	(225)	(183)
Proceeds from accounts receivable securitization program	48	200	0
Repayments under accounts receivable securitization program	(48)	0	0
Repurchase of common stock	(200.1)	(250)	0
Payment of debt issuance costs	0	0	(22.7)
Purchase of interest rate caps	(1.9)	0	(13.2)
Net proceeds from issuance of common stock pursuant to employee stock plans	49	38.5	70
Payments under capital lease obligations	(0.9)	0	0
Payment of minimum tax withholdings on net share settlements of equity awards	(19.7)	(16.4)	(12.9)
Net cash used in financing activities	(309.2)	(670.7)	(947.4)
Effect of exchange rate changes on cash and cash equivalents	7.3	(2)	(8.1)
Net increase (decrease) in cash and cash equivalents	(7.8)	57.1	(244.8)
Cash and cash equivalents, beginning of period	548.4	491.3	736.1
Cash and cash equivalents, end of period	$ 540.6	$ 548.4	$ 491.3

Operations

Operations	12 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Operations	Operations Hologic, Inc. (the “Company” or “Hologic”) develops, manufactures and supplies premium diagnostics products, medical imaging systems and surgical products with an emphasis on women's health. On March 22, 2017, the Company acquired Cynosure, Inc. ("Cynosure"). Cynosure is a developer, manufacturer and supplier of a broad array of light-based aesthetic and medical treatment systems. The products are used to provide a diverse range of treatment applications such as non-invasive body contouring, hair removal, skin revitalization and scar reduction, as well as the treatment of vascular lesions. The Cynosure business is referred to as Medical Aesthetics and operates as a separate business segment. As a result of the Cynosure acquisition, the Company operates in five segments: Diagnostics, Breast Health, Medical Aesthetics, GYN Surgical and Skeletal Health.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. The Company’s fiscal year ends on the last Saturday in September. Fiscal 2017 , 2016 and 2015 ended on September 30, 2017 , September 24, 2016 and September 26, 2015 , respectively. Fiscal 2017 is a 53-week year and fiscal 2016 and 2015 were 52-week years. Subsequent Events Consideration The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence for certain estimates or to identify matters that may require additional disclosure. Subsequent events have been evaluated as required. There were no material recognized or unrecognized subsequent events recorded in the consolidated financial statements as of and for the year ended September 30, 2017, except for the Company entering into the Amended and Restated Credit Agreement and issuance of its 2025 Notes in October 2017. For additional information, please refer to Note 5. Management’s Estimates and Uncertainties The preparation of financial statements in conformity with U.S. generally accepted accounting principles ("GAAP") requires management to make significant estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions by management affect the Company’s revenue recognition for multiple element arrangements, allowance for doubtful accounts, the net realizable value of inventory, estimated fair value of cost-method equity investments, valuations, purchase price allocations and contingent consideration related to business combinations, expected future cash flows including growth rates, discount rates, terminal values and other assumptions and estimates used to evaluate the recoverability of long-lived assets and goodwill, estimated fair values of intangible assets and goodwill, amortization methods and periods, warranty reserves, certain accrued expenses, restructuring and other related charges, stock-based compensation, contingent liabilities, tax reserves, deferred tax rates and recoverability of the Company’s net deferred tax assets and related valuation allowances. Although the Company regularly assesses these estimates, actual results could differ materially from these estimates. Changes in estimates are recorded in the period in which they become known. The Company bases its estimates on historical experience and various other assumptions that it believes to be reasonable under the circumstances. The Company is subject to a number of risks similar to those of other companies of similar size in its industry, including dependence on third-party reimbursements to support the markets of the Company’s products, early stage of development of certain products, rapid technological changes, recoverability of long-lived assets (including intangible assets and goodwill), competition, stability of world financial markets, ability to obtain regulatory approvals, changes in the regulatory environment, limited number of suppliers, customer concentration, integration of acquisitions, substantial indebtedness, government regulations, management of international activities, protection of proprietary rights, patent and other litigation, dependence on contract manufacturers and dependence on key individuals. Cash Equivalents Cash equivalents are highly liquid investments with insignificant interest rate risk and maturities of three months or less at the time of acquisition. Marketable Securities The Company’s marketable securities as of September 30, 2017 and September 24, 2016 are comprised solely of equity securities and as of September 26, 2015 also included mutual funds. The equity securities are investments in the common stock of publicly traded companies, and the mutual funds were used to fund a portion of the Company's deferred compensation plan. The equity securities are classified as available-for-sale and are recorded at fair value with the unrealized gains or losses, net of tax, recorded within accumulated other comprehensive income (loss), which is a component of stockholders’ equity. The mutual funds were classified as trading and recorded at fair value with unrealized gains and losses recorded in other income (expense), net in the Consolidated Statements of Income. The Company periodically reviews its marketable equity securities classified as available-for-sale for other-than-temporary declines in fair value below carrying value, or whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. The determination that a decline is other-than-temporary is, in part, subjective and influenced by many factors. When assessing marketable equity securities for other-than-temporary declines in fair value, the Company considers factors including: the significance of the decline in value compared to the carrying value; the underlying factors contributing to a decline in the price of the security; how long the market value of the investment has been less than its carrying value; any market conditions that impact liquidity; the views of external investment analysts; the financial condition and near-term prospects of the investee; any news or financial information that has been released specific to the investee; and the outlook for the overall industry in which the investee operates. In the fourth quarters of fiscal 2016 and 2015, the Company concluded that the decline in fair value of one of its marketable securities was other-than-temporary based on the length of time the security's market value was significantly below its carrying value and recorded impairment charges of $1.1 million and $7.8 million , respectively. No impairment charges were recorded in fiscal 2017. The following reconciles cost basis to fair market value. Cost Gross Unrealized Gross Unrealized Other Than Temporary Impairment Fair Value As of September 30, 2017 $ 0.7 $ — $ (0.6 ) $ — $ 0.1 As of September 24, 2016 $ 2.4 $ — $ (0.3 ) $ (1.1 ) $ 1.0 As of September 26, 2015 $ 16.1 $ 7.2 $ (0.3 ) $ (7.8 ) $ 15.2 In connection with the acquisition of Cynosure, the Company assumed $82.9 million of short and long-term marketable securities, which were classified as available-for-sale and primarily comprised of state and municipal bonds and U.S. treasury notes. During fiscal 2017, the Company liquidated these investments. In the first quarter of fiscal 2016, the Company sold all of its shares in one of its marketable securities and recorded a realized gain of $25.1 million in other income (expense), net. Concentrations of Credit Risk Financial instruments that subject the Company to credit risk primarily consist of cash and cash equivalents, cost-method equity investments, and trade accounts receivable. The Company invests its cash and cash equivalents with high credit quality financial institutions. The Company’s customers are principally located in the United States, Europe and Asia. The Company performs ongoing credit evaluations of the financial condition of its customers and generally does not require collateral. Although the Company is directly affected by the overall financial condition of the healthcare industry, as well as global economic conditions, management does not believe significant credit risk exists as of September 30, 2017 . The Company generally has not experienced any material losses related to receivables from individual customers or groups of customers in the healthcare industry. The Company maintains an allowance for doubtful accounts based on accounts past due and historical collection experience. There were no customers with balances greater than 10% of accounts receivable as of September 30, 2017 and September 24, 2016 , or any customers that represented greater than 10% of consolidated revenues for fiscal years 2017 , 2016 and 2015 (see Note 13). Supplemental Cash Flow Statement Information Years ended September 30, 2017 September 24, 2016 September 26, 2015 Cash paid during the period for income taxes $ 867.8 $ 184.8 $ 168.7 Cash paid during the period for interest $ 102.4 $ 104.0 $ 143.0 Inventories Inventories are valued at the lower of cost or market on a first in, first out basis. Work-in-process and finished goods inventories consist of materials, labor and manufacturing overhead. The valuation of inventory requires management to estimate excess and obsolete inventory. The Company employs a variety of methodologies to determine the net realizable value of its inventory. Provisions for excess and obsolete inventory are primarily based on management’s estimates of forecasted sales, usage levels and expiration dates, as applicable for disposable products. A significant change in the timing or level of demand for the Company’s products compared to forecasted amounts may result in recording additional charges for excess and obsolete inventory in the future. The Company records charges for excess and obsolete inventory within cost of product revenues. Inventories consisted of the following: September 30, 2017 September 24, 2016 Raw materials $ 95.7 $ 96.4 Work-in-process 45.0 51.7 Finished goods 190.9 126.6 $ 331.6 $ 274.7 Property, Plant and Equipment Property, plant and equipment is recorded at cost less allowances for depreciation. The straight-line method of depreciation is used for all property and equipment. Property, plant and equipment consisted of the following: September 30, 2017 September 24, 2016 Equipment and software $ 422.4 $ 381.9 Equipment under customer usage agreements 368.7 334.6 Buildings and improvements 172.0 186.1 Leasehold improvements 60.6 65.6 Land 46.3 51.9 Furniture and fixtures 20.8 18.4 1,090.8 1,038.5 Less - accumulated depreciation and amortization (599.6 ) (578.3 ) $ 491.2 $ 460.2 Property, plant and equipment are depreciated over the following estimated useful lives: Asset Classification Estimated Useful Life Building and improvements 20–35 years Equipment and software 3–10 years Equipment under customer usage agreements 3–8 years Furniture and fixtures 5–7 years Leasehold improvements Shorter of the Original Term of Lease or Estimated Useful Life Equipment under customer usage agreements primarily consists of diagnostic instrumentation and imaging equipment located at customer sites but owned by the Company. Generally, the customer has the right to use the equipment for a period of time provided they meet certain agreed to conditions. The Company recovers the cost of providing the equipment from the sale of disposables. The depreciation costs associated with equipment under customer usage agreements are charged to cost of product revenues over the estimated useful life of the equipment. The costs to maintain the equipment in the field are charged to cost of product revenue as incurred. The Company has identified certain software acquired in the Cynosure acquisition that will be discontinued and has shortened the useful life. As such, the Company accelerated depreciation of the asset resulting in an additional $3.0 million of expense recorded in fiscal 2017, and the Company expects to record $5.9 million of incremental expense in fiscal 2018 at which time the asset will be abandoned. Long-Lived Assets The Company reviews its long-lived assets, which includes property, plant and equipment and identifiable intangible assets (see below for discussion of intangible assets), for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable in accordance with ASC 360-10-35-15, Property, Plant and Equipment—Impairment or Disposal of Long-Lived Assets (ASC 360). Recoverability of these assets is evaluated by comparing the carrying value of the assets to the undiscounted cash flows estimated to be generated by those assets over their remaining economic life. If the undiscounted cash flows are not sufficient to recover the carrying value of the assets, the assets are considered impaired. The impairment loss is measured by comparing the fair value of the assets to their carrying value. Fair value is determined by either a quoted market price, if any, or a value determined by a discounted cash flow technique. Business Combinations and Acquisition of Intangible Assets The Company accounts for the acquisition of a business in accordance with ASC 805, Business Combinations (ASC 805). Amounts paid for each acquisition are allocated to the assets acquired and liabilities assumed based on their fair values at the date of acquisition. The Company determines the fair value of acquired intangible assets based on detailed valuations that use certain information and assumptions provided by management. The Company allocates any excess purchase price over the fair value of the net tangible and intangible assets acquired to goodwill. The Company uses the income approach to determine the fair value of developed technology and in-process research and development ("IPR&D") acquired in a business combination. This approach determines fair value by estimating the after-tax cash flows attributable to the respective asset over its useful life and then discounting these after-tax cash flows back to a present value. The Company bases its revenue assumptions on estimates of relevant market sizes, expected market growth rates, expected trends in technology and expected product introductions by competitors. Developed technology represents patented and unpatented technology and know-how. The value of the in-process projects is based on projects’ stage of completion, the complexity of the work completed as of the acquisition date, the projected costs to complete, the contribution of core technologies and other acquired assets, the expected introduction date, the estimated cash flows to be generated upon commercial release and the estimated useful life of the technology. The Company believes that the estimated developed technology and IPR&D amounts represent the fair value at the date of acquisition and do not exceed the amount a third-party would pay for the assets. The Company also uses the income approach, as described above, to determine the estimated fair value of certain other identifiable intangible assets including customer relationships, distribution agreements, trade names and business licenses. Customer relationships represent established relationships with customers, which provide a ready channel for the sale of additional products and services. Trade names represent acquired company and product names, and distribution agreements generally pertain to exclusive distribution of certain products manufactured by third parties Intangible Assets and Goodwill Intangible Assets Intangible assets are initially recorded at fair value and stated net of accumulated amortization and impairments. The Company amortizes its intangible assets that have finite lives using either the straight-line method, or if reliably determinable, based on the pattern in which the economic benefit of the asset is expected to be utilized. Amortization is recorded over the estimated useful lives ranging from 2 to 30 years. The Company evaluates the realizability of its definite lived intangible assets whenever events or changes in circumstances or business conditions indicate that the carrying value of these assets may not be recoverable based on expectations of future undiscounted cash flows for each asset group. If the carrying value of an asset or asset group exceeds its undiscounted cash flows, the Company estimates the fair value of the assets, generally utilizing a discounted cash flow analysis based on the present value of estimated future cash flows to be generated by the assets using a risk-adjusted discount rate. To estimate the fair value of the assets, the Company uses market participant assumptions pursuant to ASC 820, Fair Value Measurements . Indefinite lived intangible assets, such as IPR&D assets, are required to be tested for impairment annually, or more frequently if indicators of impairment are present. The Company’s annual impairment test date is as of the first day of its fourth quarter. Intangible assets consisted of the following: September 30, 2017 September 24, 2016 Description Gross Carrying Value Accumulated Amortization Gross Carrying Value Accumulated Amortization Developed technology $ 4,528.7 $ 2,186.8 $ 3,983.7 $ 1,991.6 In-process research and development 46.0 — 3.7 — Customer relationships 552.8 393.8 1,098.9 546.2 Trade names 310.3 156.4 236.2 141.6 Distribution agreement 42.0 2.8 — — Non-competition agreements 1.5 0.1 — — Business licenses 2.4 2.2 2.4 2.1 $ 5,483.7 $ 2,742.1 $ 5,324.9 $ 2,681.5 During the second quarter of fiscal 2017, the Company divested its blood screening business and net book value of $154.0 million of developed technology and $387.7 million of customer relationship assets were disposed of (see Note 13). In addition, in the second quarter of fiscal 2017, the Company acquired Cynosure and recorded an aggregate of $994.0 million of intangible assets (see Note 3). In the third quarter of fiscal 2017, the Company acquired Medicor and recorded $5.4 million of intangible assets. In addition, during the third quarter of fiscal 2017, the Company obtained CE approval for its last in-process research and development project acquired in the Gen-Probe Incorporated acquisition and transferred $3.7 million to developed technology. In the third quarter of fiscal 2016, the Company accelerated the amortization of the Cystic Fibrosis developed technology asset of $6.2 million as a result of discontinuing this product line. In the second quarter of fiscal 2016, the Company acquired certain intellectual property for $4.8 million , which was recorded in developed technology. Amortization expense related to developed technology is classified as a component of cost of product revenues—amortization of intangible assets. Amortization expense related to customer relationships and contracts, trade names, and business licenses is classified as a component of amortization of intangible assets within operating expenses. The estimated amortization expense at September 30, 2017 for each of the five succeeding fiscal years was as follows: Fiscal 2018 $ 376.6 Fiscal 2019 $ 364.9 Fiscal 2020 $ 353.6 Fiscal 2021 $ 332.2 Fiscal 2022 $ 319.8 Goodwill In accordance with ASC 350, Intangibles—Goodwill and Other (ASC 350), the Company tests goodwill for impairment annually at the reporting unit level and between annual tests if events and circumstances indicate it is more likely than not that the fair value of a reporting unit is less than its carrying value. Events that could indicate impairment and trigger an interim impairment assessment include, but are not limited to, current economic and market conditions, including a decline in market capitalization, a significant adverse change in legal factors, business climate, operational performance of the business or key personnel, and an adverse action or assessment by a regulator. In performing the impairment test, the Company utilizes the two-step approach prescribed under ASC 350. The first step requires a comparison of the carrying value of each reporting unit to its estimated fair value. To estimate the fair value of its reporting units for Step 1, the Company primarily utilizes the income approach. The income approach is based on a DCF analysis and calculates the fair value by estimating the after-tax cash flows attributable to a reporting unit and then discounting the after-tax cash flows to present value using a risk-adjusted discount rate. Assumptions used in the DCF require significant judgment, including judgment about appropriate discount rates and terminal values, growth rates, and the amount and timing of expected future cash flows. The forecasted cash flows are based on the Company’s most recent budget and strategic plan and for years beyond this period, the Company’s estimates are based on assumed growth rates expected as of the measurement date. The Company believes its assumptions are consistent with the plans and estimates used to manage the underlying businesses. The discount rates used are intended to reflect the risks inherent in future cash flow projections and are based on estimates of the weighted-average cost of capital (“WACC”) of market participants relative to each respective reporting unit. The market approach considers comparable market data based on multiples of revenue or earnings before interest, taxes, depreciation and amortization (“EBITDA”) and is primarily used as a corroborative analysis to the results of the DCF analysis. The Company believes its assumptions used to determine the fair value of its reporting units are reasonable. If different assumptions were used, particularly with respect to forecasted cash flows, terminal values, WACCs, or market multiples, different estimates of fair value may result and there could be the potential that an impairment charge could result. Actual operating results and the related cash flows of the reporting units could differ from the estimated operating results and related cash flows. If the carrying value of a reporting unit exceeds its estimated fair value, the Company is required to perform the second step of the goodwill impairment test to measure the amount of impairment loss, if any. The second step of the goodwill impairment test compares the implied fair value of a reporting unit’s goodwill to its carrying value. The implied fair value of goodwill is derived by performing a hypothetical purchase price allocation for the impaired reporting unit as of the measurement date and allocating the reporting unit’s estimated fair value to its assets and liabilities. The residual amount from performing this allocation represents the implied fair value of goodwill. To the extent this amount is below the carrying value of goodwill, an impairment charge is recorded. The Company conducted its fiscal 2017 impairment test on the first day of the fourth quarter, and as noted above used DCF and market approaches to estimate the fair value of its reporting units as of July 2, 2017, and ultimately used the fair value determined by the DCF approach in making its impairment test conclusions. The Company believes it used reasonable estimates and assumptions about future revenue, cost projections, cash flows, market multiples and discount rates as of the measurement date. As a result of completing Step 1, all of the Company's reporting units had fair values exceeding their carrying values, and as such, Step 2 of the impairment test was not required. For illustrative purposes, had the fair value of each of the reporting units been lower by 10% , all of the reporting units, except the Company's Medical Aesthetics reporting unit, would still have passed Step 1 of the goodwill impairment test. This reporting unit had a fair value as of the measurement date that exceeded its carrying value by 2% with goodwill of $683.5 million . The Company acquired Cynosure, which is the sole business in Medical Aesthetics, on March 22, 2017. In connection with the Company's annual strategic planning process and annual goodwill impairment test, it lowered its estimated financial projections for this business as a result of its current operating performance being below expectations, which the Company primarily attributes to the significant turnover in the U.S. sales force in 2017. In the event, future operating performance is below forecasted projections, or there are negative changes to long-term growth rates or if discount rates increase, these factors could result in a decline in the fair value of the reporting unit and the Company may be required to record a goodwill impairment charge. At September 30, 2017 , the Company believes that its other reporting units, with goodwill aggregating $2.49 billion , was not at risk of failing Step 1 of the goodwill impairment test based on the current forecasts. The Company conducted its fiscal 2016 and 2015 impairment tests on the first day of the respective year's fourth quarter, and as noted above used DCF and market approaches to estimate the fair value of its reporting units as of June 26, 2016 and June 28, 2015, respectively, and ultimately used the fair value determined by the DCF approach in making its impairment test conclusions. As a result of completing Step 1, all of the Company's reporting units had fair values exceeding their carrying values, and as such, Step 2 of the impairment test was not required. A rollforward of goodwill activity by reportable segment from September 24, 2016 to September 30, 2017 is as follows: Diagnostics Breast Health Medical Aesthetics GYN Surgical Skeletal Health Total Balance at September 24, 2016 $ 1,148.2 $ 631.8 $ — $ 1,015.0 $ 8.1 $ 2,803.1 Acquisitions — 8.9 683.5 — — 692.4 Sale of blood screening business (325.0 ) — — — — (325.0 ) Foreign currency and other adjustments (0.2 ) 0.8 — 0.1 — 0.7 Balance at September 30, 2017 $ 823.0 $ 641.5 $ 683.5 $ 1,015.1 $ 8.1 $ 3,171.2 Other Assets Other assets consisted of the following: September 30, 2017 September 24, 2016 Other Assets Life insurance contracts $ 41.0 $ 36.0 Capitalized software 12.3 10.0 Manufacturing access fees 7.1 9.6 Cost-method equity investments 3.0 3.5 Deferred tax assets 9.1 9.3 Other 24.5 15.3 $ 97.0 $ 83.7 Life insurance contracts were purchased in connection with the Company’s Nonqualified Deferred Compensation Plan (“DCP”) and are recorded at their cash surrender value (see Note 9 for further discussion). Capitalized software relates to development costs incurred related to software embedded in the Company's products. The manufacturing access fees are related to a manufacturing supply and purchase agreement for our Aptima HPV products and are being amortized over the term of the agreement. Research and Software Development Costs Costs incurred for the research and development of the Company’s products are expensed as incurred. Nonrefundable advance payments for goods or services to be received in the future by the Company for use in research and development activities are deferred. The deferred costs are expensed as the related goods are delivered or the services are performed. The Company accounts for the development costs of software embedded in the Company’s products in accordance with ASC 985, Software. Costs incurred in the research, design and development of software embedded in products to be sold to customers are charged to expense until technological feasibility of the ultimate product to be sold is established. The Company’s policy is that technological feasibility is achieved when a working model, with the key features and functions of the product, is available for customer testing. Software development costs incurred after the establishment of technological feasibility and until the product is available for general release are capitalized, provided recoverability is reasonably assured. Capitalized software development costs are amortized over their estimate useful life and recorded within cost of revenues - product. Foreign Currency Translation The financial statements of the Company’s foreign subsidiaries are translated in accordance with ASC 830, Foreign Currency Matters. The reporting currency for the Company is the U.S. dollar. The functional currency of the Company’s foreign subsidiaries is determined based on the guidance in ASC 830. The majority of the Company's foreign subsidiaries' functional currency is the applicable local currency, although certain of the Company's foreign subsidiaries' functional currency is the U.S. dollar based on the nature of their operations or functions. Assets and liabilities of subsidiaries whose functional currency is the local currency are translated at the exchange rate in effect at each balance sheet date. Before translation, the Company re-measures foreign currency denominated assets and liabilities, including inter-company accounts receivable and payable, into the functional currency of the respective entity, resulting in unrealized gains or losses recorded in other income (expense), net in the Consolidated Statements of Income. Revenues and expenses are translated using average exchange rates during the respective period. Foreign currency translation adjustments are accumulated as a component of other comprehensive income (loss) as a separate component of stockholders’ equity. Gains and losses arising from transactions denominated in foreign currencies are included in other income (expense), net in the Consolidated Statements of Income and were not significant in any of the reporting periods presented. Accumulated Other Comprehensive Income (Loss) Other comprehensive income (loss) includes certain transactions that have generally been reported in the statement of stockholders’ equity. The following tables summarize the components and changes in accumulated balances of other comprehensive income for the periods presented: Year Ended September 30, 2017 Year Ended September 24, 2016 Foreign Currency Translation Marketable Securities Pension Plans Hedged Interest Rate Caps Total Foreign Currency Translation Marketable Securities Pension Plans Hedged Interest Rate Caps Total Beginning Balance $ (26.1 ) $ (0.3 ) $ (2.5 ) $ (3.4 ) $ (32.3 ) $ (15.7 ) $ 6.9 $ (1.8 ) $ (3.9 ) $ (14.5 ) Other comprehensive loss before reclassifications 7.6 2.3 0.9 0.8 11.6 (10.4 ) (1.1 ) (0.7 ) (3.4 ) (15.6 ) (Gains) charges reclassified to statement of income — (2.4 ) — 6.9 4.5 — (6.1 ) — 3.9 (2.2 ) Ending Balance $ (18.5 ) $ (0.4 ) $ (1.6 ) $ 4.3 $ (16.2 ) $ (26.1 ) $ (0.3 ) $ (2.5 ) $ (3.4 ) $ (32.3 ) In the first quarter of fiscal 2017, one of the Company's cost-method equity investments became a marketable security, and the Company recorded the increase in value of $4.0 million to other comprehensive income. In the second quarter of fiscal 2017, the Company sold this marketable security and recorded a gain of $3.8 million in other income (expense), net. In the first quarter of fiscal 2016, the Company sold all of its shares in one of its marketable securities and recorded a realized gain of $25.1 million in other income (expense), net and resulted in reclassifying a $7.2 million gain out of other comprehensive income (loss) to other income (expense), net. In the fourth quarter of fiscal 2016, the Company recorded a $1.1 million other-than-temporary impairment charge, and this amount was reclassified out of other comprehensive income (loss) to other income (expense), net. During fiscal 2015, the Company reclassified $9.6 million out of accumulated other comprehensive income to restructuring and divestiture charges related to writing off the cumulative translation adjustment in connection with its substantial liquidation of the MRI breast coils product line (see Note 4). In addition, during fiscal 2015 the Company reclassified $7.8 million out of accumulated other comprehensive income to other (expense) income, net for the other-than-temporary impairment of a marketable security. Derivatives Interest Rate Cap - Cash Flow Hedge The Company is exposed to certain risks arising from both its business operations and economic conditions. The Company manages its exposure to some of its interest rate risk through the use of interest rate caps, which are derivative financial instruments. The Company does not use derivatives for speculative purposes. For a derivative that is designated as a cash flow hedge, changes in the fair value of the derivative are recognized in accumulated other comprehensive income ("AOCI") to the extent the derivative is effective at offsetting the changes in the cash flows being hedged until the hedged item affects earnings. To the extent there is any hedge ineffectiveness, changes in fair value relating to the ineffective portion are immediately recognized in earnings in other income (expense) in the Consolidated Statements of Income. During fiscal 2015, the Company entered into separate interest rate cap agreements with multiple counter-parties to help mitigate the interest rate volatility associated with the variable rate interest on its credit facilities under its Prior Credit Agreement, which was replaced by the Credit Agreement in 2015 (see Note 5). Interest rate cap agreements provide the right to receive cash if the reference

Business Combinations

Business Combinations	12 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Business Combinations	Business Combinations Cynosure, Inc. On March 22, 2017, the Company completed the acquisition of Cynosure and acquired all of the outstanding shares of Cynosure. Pursuant to the terms and conditions of the merger agreement, each share of common stock of Cynosure outstanding immediately prior to the effective time of the acquisition was canceled and converted into the right to receive $66.00 in cash, except for 1.2 million shares the holder of which demanded appraisal rights (the "dissenting shares"). In addition, all outstanding restricted stock units, performance stock units, and stock options were canceled and converted into the right to receive $66.00 per share in cash less the applicable exercise price, as applicable. The acquisition was funded through available cash, and the total purchase price was $1.66 billion . The Company incurred $18.8 million of direct transaction costs recorded within general and administrative expenses. Cynosure, headquartered in Westford, Massachusetts, develops, manufactures, and markets aesthetic treatment systems that enable plastic surgeons, dermatologists and other medical practitioners to perform non-invasive and minimally invasive procedures to remove hair, treat vascular and benign pigmented lesions, remove multi-colored tattoos, revitalize the skin, reduce fat through laser lipolysis, reduce cellulite, clear nails infected by toe fungus, ablate sweat glands and improve women’s health. Cynosure also markets radiofrequency (RF) energy-sourced medical devices for precision surgical applications such as facial plastic and general surgery, gynecology, ear, nose, and throat procedures, ophthalmology, oral and maxillofacial surgery, podiatry and proctology. Cynosure's results of operations are reported in the Company's Medical Aesthetics reportable segment from the date of acquisition and the goodwill within this reportable segment is solely related to Cynosure. The total purchase price was allocated to Cynosure’s preliminary tangible and identifiable intangible assets and liabilities based on the estimated fair values of those assets as of March 22, 2017, as set forth below. The preliminary purchase price allocation is as follows: Cash $ 107.2 Marketable securities 82.9 Accounts receivable 40.2 Inventory 121.1 Property, plant and equipment 44.1 Other assets and liabilities, net 12.2 Accounts payable and accrued expenses (75.3 ) Deferred revenue (11.2 ) Capital lease obligation (25.2 ) Identifiable intangible assets: Developed technology 736.0 In-process research and development 107.0 Distribution agreement 42.0 Customer relationships 35.0 Trade names 74.0 Deferred income taxes, net (315.7 ) Goodwill 683.5 Purchase Price $ 1,657.8 In performing the preliminary purchase price allocation, the Company considered, among other factors, the intended future use of acquired assets, analysis of historical financial performance and estimates of future performance of Cynosure’s business. The Company has not yet obtained all of the information related to the fair value of the acquired assets and liabilities, primarily taxes, to finalize the purchase price allocation. As part of the preliminary purchase price allocation, the Company has determined the identifiable intangible assets are developed technology, in-process research and development ("IPR&D"), a distribution agreement, customer relationships, and trade names. The preliminary fair value of the intangible assets has been estimated using the income approach, and the cash flow projections were discounted using rates ranging from 11% to 12% , except for the IPR&D assets in which the Company used a range of 14% to 22% . The cash flows are based on estimates used to price the transaction, and the discount rates applied were benchmarked with reference to the implied rate of return from the transaction model and the weighted average cost of capital. The developed technology assets are comprised of know-how, patents and technologies embedded in Cynosure's products and relate to currently marketed products. The developed technology assets comprise the significant product families of Cynosure, primarily SculpSure, Icon, and PicoSure. IPR&D projects relate to in-process projects that have not reached technological feasibility as of the acquisition date and have no alternative future use. The primary basis for determining technological feasibility of these projects is obtaining regulatory approval to market the underlying product or expected commercial release depending on the project. The Company recorded, on a preliminary basis, $107.0 million of IPR&D related to three projects, which were expected to be completed during fiscal 2018 and 2019 with a preliminary cost to complete of approximately $18.0 million . During the fourth quarter of fiscal 2017, the Company obtained regulatory approval for two projects with an aggregate fair value of $61.0 million and these assets were reclassified to developed technology. The remaining project is expected to be completed during fiscal 2019 with an estimated cost to complete of approximately $4.0 million . Given the uncertainties inherent with product development and introduction, there can be no assurance that any of the Company's product development efforts will be successful, completed on a timely basis or within budget, if at all. All of the IPR&D assets were valued using the multiple-period excess earnings method approach. The distribution agreement intangible asset primarily relates to Cynosure's exclusive distribution rights for the MonaLisa Touch device in certain geographic regions. The customer relationships intangible asset pertains to Cynosure's relationships with its end customers and related service arrangements and distributors throughout the world. Trade names relate to the Cynosure corporate name and primary product names, and the Company used the Relief-from-Royalty Method to estimate the fair value of this asset. Developed technology, distribution agreement, customer relationships and trade names are being amortized on a straight-line basis over a weighted average period of 11.8 years, 8 years, 7.7 years and 8.9 years, respectively. The preliminary calculation of the excess of the purchase price over the estimated fair value of the tangible net assets and intangible assets acquired was recorded to goodwill. The factors contributing to the recognition of the preliminary amount of goodwill are based on several strategic and synergistic benefits that are expected to be realized from the Cynosure acquisition. These benefits include the expectation that the Company's entry into the aesthetics market will significantly broaden the Company's offering in women's health. The combined company is expected to benefit from a broader global presence, synergistic utilization of Hologic's direct sales force, primarily its GYN Surgical sales force, with certain Cynosure products, and the Company's entry into an adjacent cash-pay segment. None of the goodwill is expected to be deductible for income tax purposes. Cynosure's revenue and pre-tax loss, which excludes acquisition expenses incurred by the Company, for the period from the acquisition date to September 30, 2017 , were $207.5 million and $96.4 million , respectively. The pre-tax loss includes amortization expense, the impact of the step-up in inventory, retention and integration expenses including legal and consulting fees, and restructuring charges. The following unaudited pro forma information presents the combined financial results for the Company and Cynosure as if the acquisition of Cynosure had been completed at the beginning of the prior fiscal year, September 26, 2015: Twelve Months Ended Twelve Months Ended September 30, 2017 September 24, 2016 (unaudited) (unaudited) Revenue $ 3,241.4 $ 3,244.6 Net income $ 768.5 $ 252.3 Basic earnings per common share $ 2.75 $ 0.90 Diluted earnings per common share $ 2.69 $ 0.88 The unaudited pro forma information for fiscal 2017 and 2016 was calculated after applying the Company's accounting policies and the impact of acquisition date fair value adjustments. Fiscal 2017 unaudited pro forma net income was adjusted to exclude acquisition-related transaction costs, restructuring and retention costs solely related to the acquisition, and the impact of the fair value step-up to inventory. These expenses have been added to fiscal 2016 unaudited pro forma net income. These pro forma condensed consolidated financial results have been prepared for comparative purposes only and include certain adjustments to reflect pro forma results of operations as if the acquisition occurred on September 27, 2015, such as fair value adjustments to inventory and property, plant and equipment, increased expenses for restructuring charges and retention costs, and increased amortization for the fair value of acquired intangible assets. The pro forma information does not reflect the effect of costs, other than restructuring, or synergies that would have been expected to result from the integration of the acquisition. The pro forma information does not purport to be indicative of the results of operations that actually would have resulted had the combination occurred at the beginning of each period presented, or of future results of the consolidated entities. Medicor Medical Supply On April 7, 2017, the Company completed the acquisition of MMS Medicor Medical Supplies GmbH ("Medicor") for a purchase price of approximately $19.0 million , which includes a working capital adjustment of $2.0 million that was paid in the fourth quarter of fiscal 2017, and a holdback of $1.9 million that is payable two years from the date of acquisition. Medicor was a long-standing distributor of the Company's Breast and Skeletal Health products in Germany, Austria and Switzerland. Based on the Company's preliminary valuation, it has allocated $5.4 million of the purchase price to the preliminary value of intangible assets, which primarily consist of customer relationships and have a weighted average life of 7.7 years , and $8.9 million to goodwill. The remaining $4.7 million of purchase price has been allocated to the acquired tangible assets and liabilities. The allocation of the purchase price is preliminary as the Company continues to gather information supporting the acquired assets and liabilities.

Restructuring and Divestiture C

Restructuring and Divestiture Charges	12 Months Ended
	Sep. 30, 2017
Restructuring and Related Activities [Abstract]
Restructuring and Divestiture Charges	Restructuring and Divestiture Charges The Company evaluates its operations for opportunities to improve operational effectiveness and efficiency, including facility and operations consolidation, and to better align expenses with revenues. As a result of these assessments, the Company has undertaken various restructuring actions which are described below. The following table displays charges taken related to restructuring actions in fiscal 2017 , 2016 and 2015 and a rollforward of the charges to the accrued balances as of September 30, 2017 : Fiscal 2017 Actions Fiscal 2016 Actions Fiscal 2015 Actions Fiscal 2014 Actions Other Charges Total Restructuring and Divestiture Charges Fiscal 2015 charges: Workforce reductions $ — $ — $ 10.0 $ 6.0 $ 0.3 $ 16.3 Facility closure costs — — — 2.0 0.6 2.6 Fiscal 2015 restructuring charges $ — $ — $ 10.0 $ 8.0 $ 0.9 $ 18.9 Divestiture net charges 9.6 Fiscal 2015 restructuring and divestiture charges $ 28.5 Fiscal 2016 charges: Workforce reductions $ — $ 10.5 $ — $ — $ — $ 10.5 Fiscal 2016 restructuring charges $ — $ 10.5 $ — $ — $ — $ 10.5 Fiscal 2017 charges: Workforce reductions $ 8.5 $ — $ — $ — $ — $ 8.5 Facility closure costs — 4.8 — — — 4.8 Other — — — — — — Fiscal 2017 restructuring charges $ 8.5 $ 4.8 $ — $ — $ — $13.3 Fiscal 2017 Actions Fiscal 2016 Actions Fiscal 2015 Actions Fiscal 2014 Actions Other Charges Total Rollforward of Accrued Restructuring Balance as of September 27, 2014 $ — $ — $ — $ 12.0 $ 4.9 $ 16.9 Fiscal 2015 restructuring charges $ — $ — $ 10.0 $ 8.0 $ 0.9 $ 18.9 Stock-based compensation — — (4.1 ) — — (4.1 ) Severance payments — — (2.8 ) (16.2 ) (4.9 ) (23.9 ) Other payments — — — (1.3 ) (0.8 ) (2.1 ) Balance as of September 26, 2015 $ — $ — $ 3.1 $ 2.5 $ 0.1 $ 5.7 Fiscal 2016 restructuring charges $ — $ 10.5 $ — $ — $ — $ 10.5 Stock-based compensation — (0.4 ) — — — (0.4 ) Severance payments — (4.6 ) (2.9 ) (1.4 ) (0.1 ) (9.0 ) Other payments — — — (0.5 ) — (0.5 ) Balance as of September 24, 2016 $ — $ 5.5 $ 0.2 $ 0.6 $ — $ 6.3 Fiscal 2017 restructuring charges $ 8.5 $ 4.8 $ — $ — $ — $ 13.3 Severance payments (1.0 ) (5.4 ) (0.2 ) — — (6.6 ) Other payments — (1.2 ) — (0.3 ) — (1.5 ) Balance as of September 30, 2017 $ 7.5 $ 3.7 $ — $ 0.3 $ — $ 11.5 Fiscal 2017 Actions During the second quarter of fiscal 2017, the Company completed its acquisition of Cynosure. In connection with the acquisition, the Company decided to terminate certain Cynosure executives in the second quarter of fiscal 2017 and recorded $1.5 million in severance and benefits charges. During the third and fourth quarters of fiscal 2017, the Company terminated additional executives and employees and recorded $4.3 million and $1.3 million , respectively, in severance and benefits charges. The charges were recorded pursuant to ASC 712, Compensation-Nonretirement Postemployment Benefits (ASC 712) or ASC 420, Exit or Disposal Cost Obligations (ASC 420) depending on the executive. Additional terminations may occur, but the Company does not have a formal plan at this time, nor does it expect any resulting charges to be material. During the fourth quarter of fiscal 2017, the decision was made to reduce headcount and related costs in R&D within Breast Health and to eliminate certain manufacturing personnel, primarily in Diagnostics. The majority of employees were notified of termination and related benefits in the fourth quarter of fiscal 2017, and the Company recorded these charges pursuant to ASC 420 as the benefits qualify as one-time termination benefits. As such, the Company recorded a charge for severance and benefits for these employees of $1.4 million in the fourth quarter. Fiscal 2016 Actions During the fourth quarter of fiscal 2016, the Company decided to initiate a cost reduction initiative in part of its Diagnostic's reportable segment, resulting in the termination of certain employees. The majority of employees were notified of termination and related benefits in the fourth quarter of fiscal 2016, and the Company recorded these charges pursuant to ASC 420 as the benefits qualify as one-time termination benefits. As such, the Company recorded a charge for severance and benefits of $0.9 million in the fourth quarter. This action was completed and no additional charges were recorded in fiscal 2017. During the third quarter of fiscal 2015, the Company decided to close its Bedford, Massachusetts facility where it manufactured its Skeletal Health products and provided certain support manufacturing services for its Breast Health segment. The manufacturing of the Skeletal Health products was outsourced to a third-party, and the Breast Health manufacturing services were moved to the Company's Danbury, Connecticut and Marlborough, Massachusetts facilities. In addition, research and development, sales and services support and administrative functions were moved to both Marlborough and Danbury. The transition was be substantially completed by the end of calendar year 2016. In connection with this plan, certain employees, primarily in manufacturing, were terminated. The employees were notified of termination and related benefits in the first quarter of fiscal 2016, and the Company recorded these charges pursuant to ASC 420. Employees were required to remain employed during this transition period and charges were recorded ratably over the required service period. The Company recorded $1.7 million in severance and benefits charges related to this action in fiscal 2016. This action was completed in the first quarter of fiscal 2017. In connection with shutting down the Bedford location, during the first quarter of fiscal 2017 the Company recorded $3.5 million for lease obligation charges related to a section of the facility that the Company had determined met the cease-use date criteria. The Company made certain assumptions regarding the time period it would take to obtain a subtenant and the sublease rates it could obtain. During the third quarter of fiscal 2017, the Company updated its assumption regarding the time period it will take to obtain a subtenant and as a result recorded an additional $1.3 million lease obligation charge. These estimates may vary from the actual sublease agreements executed, if at all, resulting in an adjustment to the charge. The Company has vacated other portions of the building but not the entire facility, and at this time does not meet the cease-use date criteria to record additional restructuring charges. During the first quarter of fiscal 2016, the Company began implementing a second plan to consolidate and improve operational efficiency of its international sales and marketing and field services operations and certain support functions. As a result, the Company identified and terminated certain employees during each quarter in fiscal 2016. Severance and benefits under this action were recorded pursuant to ASC 712, and ASC 420 depending on the circumstances. The Company recorded severance and benefit charges of $7.9 million in fiscal 2016 related to this plan. Fiscal 2015 Actions During each quarter of fiscal 2015, the Company continued to make executive management changes resulting in the termination of certain executives and employees on a worldwide basis. In addition, the Company continued to consolidate and close certain international offices to improve operational efficiency and reduce costs. Severance and benefit charges under these actions were recorded pursuant to ASC 712 and ASC 420 depending on the employees terminated, and the Company recorded severance and benefit charges of $10.0 million in fiscal 2015. Included in the charge was $4.1 million of stock-based compensation. No additional charges will be recorded under these actions. In connection with its review of operations, the Company decided to shut-down its manufacturing operation in China, which manufactured mammography systems for the Chinese market. As a result, the Company terminated manufacturing and research and development personnel located in China, and the severance charge was insignificant. Fiscal 2014 Actions During the first quarter of fiscal 2014, the Company implemented a cost reduction initiative comprised of reducing headcount and evaluating research projects and operating costs. In connection with this plan, the Company terminated certain employees on a worldwide basis. The Company recorded the severance and benefit charges pursuant to ASC 420 and ASC 712, depending on the employee terminated. The Company recorded $6.3 million of severance and benefit charges in the first quarter of fiscal 2014. On December 6, 2013, Stephen P. MacMillan was appointed as President, Chief Executive Officer and a director of the Company. The employment of John W. Cumming, the Company’s prior President and Chief Executive Officer, terminated upon Mr. MacMillan’s appointment. The Company provided separation benefits to Mr. Cumming pursuant to his employment letter dated July 18, 2013 resulting in a charge of $6.6 million in the first quarter of fiscal 2014, which included $4.4 million of stock-based compensation related to the acceleration of all of Mr. Cumming’s outstanding equity awards in accordance with the existing terms of Mr. Cumming’s share-based payment arrangements. In the second, third, and fourth quarters of fiscal 2014, the Company continued to make executive management changes and implement additional cost reduction initiatives resulting in the termination of certain executives and employees on a worldwide basis. In addition, in the fourth quarter of fiscal 2014 the Company decided to consolidate and close certain international offices. Severance and benefit charges under these actions were recorded pursuant to ASC 420 and ASC 712 depending on the employees terminated, and the Company recorded severance and benefit charges of $16.6 million in fiscal 2014. Included in the charge was $1.8 million of stock-based compensation for the modification of the terms of equity awards to certain employees. For those employees who continued to be employed beyond the minimum retention period, charges were recorded ratably over the estimated service period of the affected employees. During fiscal 2015, the Company recorded $6.0 million for severance and benefits costs and $2.0 million for facility closure costs related to this action. The facility closure costs primarily relate to lease obligation charges for three office locations that were vacated and the Company had met the cease-use date criteria. This action was completed in fiscal 2015. Divestiture In the fourth quarter of fiscal 2014, the Company completed the sale of its MRI breast coils product line and recorded a loss on disposal of $5.3 million . The Company also provided certain transition services through April 2015, including the manufacturing and sale of inventory to the buyer. Since all operations had ceased during the third quarter of fiscal 2015, the Company concluded that this subsidiary had been substantially liquidated and recorded a $9.6 million charge in the third quarter of fiscal 2015 related to writing off the cumulative translation adjustment related to the subsidiary.

Borrowings and Credit Arrangeme

Borrowings and Credit Arrangements	12 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Borrowings and Credit Agreements	Borrowings and Credit Agreements The Company’s borrowings consisted of the following: September 30, September 24, Current debt obligations, net of debt discount and issuance costs: Term Loan $ 121.3 $ 83.8 Revolver 345.0 — Securitization Program 200.0 200.0 Convertible Notes 484.5 12.2 Total current debt obligations 1,150.8 296.0 Long-term debt obligations, net of debt discount and issuance costs: Term Loan 1,190.5 1,308.2 2022 Senior Notes 981.6 977.7 Convertible Notes — 763.5 Total long-term debt obligations 2,172.1 3,049.4 Total debt obligations $ 3,322.9 $ 3,345.4 The debt maturity schedule for the Company’s obligations as of September 30, 2017 is as follows: 2018 2019 2020 2021 2022 2023 and Thereafter Total Term Loan $ 121.9 $ 150.0 $ 1,050.0 $ — $ — $ — $ 1,321.9 Revolver 345.0 — — — — — 345.0 Securitization Program 200.0 — — — — — 200.0 2022 Senior Notes — — — — 1,000.0 — 1,000.0 Convertible Notes (1) 488.3 — — — — 488.3 $ 1,155.2 $ 150.0 $ 1,050.0 $ — $ 1,000.0 $ — $ 3,355.2 (1) Classified based on the earliest date of redemption for each respective issuance. In addition, the balance in fiscal 2018 reflects accretion on the 2013 Notes through September 30, 2017. As discussed below, in October 2017 the Company refinanced its Credit Agreement and Term Loan which included increasing the amount outstanding to $1.5 billion , adjusting the principal payments and extending the maturity dates. In addition, the Company issued senior notes for $350 million due 2025. The above schedule does not reflect these subsequent changes to the Company's obligations. Credit Agreement On May 29, 2015, the Company and certain of its domestic subsidiaries entered into a Credit and Guaranty Agreement (the “Credit Agreement”) with Bank of America, N.A., in its capacity as Administrative Agent, Swing Line Lender and L/C Issuer, and certain other lenders party thereto (collectively, the "Lenders"). This Credit Agreement replaced the Company's existing senior secured credit facility with Goldman Sachs Bank USA, in its capacity as administrative agent and collateral agent and the lenders party thereto ("Prior Credit Agreement") entered into on August 1, 2012, and the proceeds under the Credit Agreement of $1.68 billion were used to pay off the amounts outstanding under the Prior Credit Agreement. The credit facilities ("Credit Facilities") under the Credit Agreement consisted of: • A $1.5 billion secured term loan to the Company with a final maturity date of May 29, 2020 (the “Term Loan”); and • A secured revolving credit facility under which the Borrowers (as defined below) may borrow up to $1 billion , subject to certain sublimits, with a final maturity date of May 29, 2020 (the “Revolver”). In addition to the Term Loan, the Company borrowed $175.0 million under the Revolver upon entering into the Credit Agreement that was subsequently repaid during fiscal 2016. Borrowings under the Credit Facilities bore interest, at the Company's option and in each case plus an applicable margin, as follows: • Term Loan : the Base Rate (as defined in the Credit Agreement) or the Eurocurrency Rate (i.e., the Libor rate); and • Revolver : if funded in U.S. dollars, the Base Rate or the Eurocurrency Rate, and, if funded in an alternative currency, the Eurocurrency Rate; and if requested under the swing line sublimit, the Base Rate. The applicable margin to the Base Rate and the Eurocurrency Rate was subject to specified changes depending on the total net leverage ratio as defined in the Credit Agreement. Current borrowings outstanding under the Credit Agreement bore interest at the Eurocurrency Rate plus the applicable margin, which was 1.50% per annum as of September 30, 2017. The Company was also required to pay a quarterly commitment fee on the undrawn committed amount available under the Revolver. The Company was required to make scheduled principal payments under the Term Loan in increasing amounts ranging from $18.75 million per three-month period commencing with the three-month period ending on September 25, 2015 to $37.5 million per three-month period commencing with the three-month period ending on September 28, 2018. The remaining balance of the Term Loan and amounts outstanding under the Revolver were due at maturity. In addition, subject to the terms and conditions set forth in the Credit Agreement, the Company could be required to make certain mandatory prepayments from specified excess cash flows from operations (to the extent the Company’s net senior secured leverage ratio exceeds a certain ratio) and from the net proceeds of specified types of asset sales (subject to certain reinvestment rights), debt issuances and insurance recoveries (subject to certain reinvestment rights) (“Mandatory Prepayments”). Mandatory Prepayments were required to be applied by the Company, first, to the Term Loan, second, to any outstanding amount under the swing line sublimit, third, to the Revolver, and fourth to any outstanding amount under a letter of credit sublimit. Subject to certain limitations, the Company could have voluntarily prepaid any of the credit facilities under the Credit Agreement without premium or penalty. Borrowings outstanding under the Credit Agreement in fiscal 2017 , 2016 and 2015 had weighted-average interest rates of 2.39% , 2.08% and 2.43% , respectively. The interest rate on the amounts outstanding at September 30, 2017 was 2.73% . Interest expense in fiscal 2017 , 2016 and 2015 aggregated $42.3 million and $40.4 million , and $54.7 million , respectively, which includes non-cash interest expense of $4.2 million , $4.4 million , and $9.0 million respectively, related to the amortization of the deferred issuance costs and accretion of the debt discount. The Credit Agreement contained affirmative and negative covenants customarily applicable to senior secured credit facilities, including covenants restricting the ability of the Borrowers and the Subsidiary Guarantors, subject to negotiated exceptions, to incur additional indebtedness and additional liens on their assets, engage in mergers or acquisitions or dispose of assets, enter into sale-leaseback transactions, pay dividends or make other distributions, voluntarily prepay other indebtedness, enter into transactions with affiliated persons, make investments, and change the nature of their businesses. The Credit Agreement also contained customary representations and warranties and events of default, including payment defaults, breach of representations and warranties, covenant defaults, cross defaults and an event of default upon a change of control of the Company. Borrowings were secured by first-priority liens on, and a first-priority security interest in, substantially all of the assets of the Company, with certain exceptions. For example, borrowings under the Credit Agreement were not secured by those accounts receivable that are transferred to the special purpose entity under the Company's Accounts Receivable Securitization program. The Credit Agreement contained total net leverage ratio and interest coverage ratio financial covenants measured as of the last day of each fiscal quarter and an excess cash flow prepayment requirement measured as of the end of each fiscal year. The total net leverage ratio was 5.50 :1.00 beginning on the Company's fiscal quarter ended September 26, 2015, and then decreased over time to 4.00 :1.00 for the quarter ending March 28, 2020. The interest coverage ratio was 3.75 :1.00 beginning on the Company's fiscal quarter ended September 26, 2015, and remained as such for each quarter thereafter. The total net leverage ratio was defined as the ratio of the Company's consolidated net debt as of the quarter end to its consolidated adjusted EBITDA (as defined in the Credit Agreement) for the four-fiscal quarter period ending on the measurement date. The interest coverage ratio was defined as the ratio of the Company's consolidated adjusted EBITDA for the prior four-fiscal quarter period ending on the measurement date to adjusted consolidated cash interest expense (as defined in the Credit Agreement) for the same measurement period. The Company was in compliance with these covenants as of September 30, 2017 , and no Mandatory Prepayments were required as of September 30, 2017 . The Company evaluated the Credit Agreement for derivatives pursuant to ASC 815, Derivatives and Hedging , and identified embedded derivatives that required bifurcation as the features are not clearly and closely related to the host instrument. The embedded derivatives were a default provision, which could require additional interest payments, and a provision requiring contingent payments to compensate the lenders for changes in tax deductions. The Company determined that the fair value of these embedded derivatives was nominal as of September 30, 2017 and September 24, 2016 . Pursuant to ASC 470, Debt (ASC 470), the accounting for the Credit Agreement was evaluated on a creditor-by-creditor basis with regard to the Prior Credit Agreement to determine whether each transaction should be accounted for as a modification or extinguishment. Certain creditors under the Prior Credit Agreement did not participate in this refinancing transaction and ceased being creditors of the Company. As a result, the Company recorded a debt extinguishment loss of $18.2 million in the third quarter of fiscal 2015 to write-off the pro-rata amount of unamortized debt discount and deferred issuance costs related to these creditors. For the remainder of the creditors, this transaction was accounted for as a modification because on a creditor-by-creditor basis the present value of the cash flows between the two debt instruments before and after the transaction was less than 10% . Pursuant to ASC 470, subtopic 50-40, third-party costs of $4.6 million related to this transaction were recorded as interest expense and $3.8 million were recorded as deferred issuance costs to be amortized over the term of the agreement. In addition, fees paid directly to the Lenders of $4.9 million were recorded as a debt discount. On May 6, 2016, the Company used the proceeds borrowed under the Securitization Program, discussed below, to repay $175.0 million owed under its Revolver. At various times during fiscal 2017, the Company borrowed $345.0 million under its Revolver in order to repay amounts owed on its convertible debt and to repurchase $200.1 million of its common stock. This amount was outstanding as of September 30, 2017 . Prior Credit Agreement On August 1, 2012, the Company and certain domestic subsidiaries (the “Guarantors”) entered into the Prior Credit Agreement with Goldman Sachs Bank USA, in its capacity as administrative and collateral agent, and the lenders party thereto (collectively, the “Prior Lenders”). The credit facilities under the Prior Credit Agreement initially consisted of: • $1.0 billion senior secured tranche A term loan (“Term Loan A”) with a final maturity date of August 1, 2017 ; • $1.5 billion secured tranche B term loan (“Term Loan B”) with a final maturity date of August 1, 2019 ; and • $300.0 million secured revolving credit facility (“Revolving Facility”) with a final maturity date of August 1, 2017 . Pursuant to the terms and conditions of the Prior Credit Agreement, the Prior Lenders committed to provide senior secured financing in an aggregate amount of up to $2.8 billion . As of the closing of the Gen-Probe Incorporated acquisition on August 1, 2012, the Company borrowed $2.5 billion aggregate principal under the term loans of the Prior Credit Agreement. On December 24, 2014, the Company voluntarily prepaid $300.0 million of the Term Loan B facility. Pursuant to ASC 470, the Company recorded a debt extinguishment loss of $6.7 million in the first quarter of fiscal 2015 to write-off the pro-rata amount of unamortized debt discount and deferred issuance costs related to this voluntary prepayment. Senior Notes 2022 Senior Notes On July 2, 2015, the Company completed a private placement of $1.0 billion aggregate principal amount of its 5.250% Senior Notes due 2022 (the “2022 Senior Notes”) at an offering price of 100% of the aggregate principal amount of the 2022 Senior Notes. The 2022 Senior Notes mature on July 15, 2022 and bear interest at the rate of 5.250% per year, payable semi-annually on January 15 and July 15 of each year, commencing on January 15, 2016. The Company used the net proceeds of the 2022 Senior Notes, plus available cash to redeem the outstanding 6.25% Senior Notes due 2020 (the "Senior Notes") in the aggregate principal amount of $1.0 billion on August 1, 2015 at an aggregate redemption price of $1.03 billion , reflecting a premium payment of $31.25 million . In addition, the Company made a final interest payment in the amount of $31.25 million for interest accrued to August 1, 2015, to holders of record of the Senior Notes as of July 15, 2015. As a result of this transaction, the Company recorded a debt extinguishment loss in the fourth quarter of fiscal 2015 of $22.3 million , which included the pro-rata premium payment and pro-rata debt issuance costs. The Company evaluated the accounting under ASC 470 at the creditor-by-creditor level to determine modification versus extinguishment accounting. The Company recorded interest expense related to the 2022 Senior Notes and Senior Notes of $57.3 million , $56.0 million , and $67.2 million and in fiscal 2017 , 2016 and 2015 , respectively, which includes non-cash interest expense of $3.9 million , $3.8 million and $2.1 million in fiscal 2017 , 2016 and 2015 , respectively, related to the amortization of the deferred financing costs. The 2022 Senior Notes were not registered, and will be not registered, under the Securities Act of 1933, as amended (the “Securities Act”), or any state securities laws, and were offered only to qualified institutional buyers in reliance on Rule 144A under the Securities Act and outside the United States in accordance with Regulation S under the Securities Act. The 2022 Senior Notes are general senior unsecured obligations of the Company and are guaranteed on a senior unsecured basis by certain domestic subsidiaries of Hologic (the “Domestic Guarantors”). The 2022 Senior Notes were issued pursuant to an indenture (the "Indenture"), dated as of July 2, 2015, among the Company, the Domestic Guarantors and Wells Fargo Bank, National Association, as trustee. The Indenture contains covenants which limit, among other things, the ability of the Company and the Domestic Guarantors to incur additional indebtedness and additional liens on their assets, engage in mergers or acquisitions or dispose of assets, pay dividends or make other distributions, enter into certain transactions with affiliated persons and to make certain investments. These covenants are subject to a number of exceptions and qualifications, including the suspension of certain of these covenants upon the 2022 Senior Notes receiving an investment grade credit rating. The Indenture does not require the Company to maintain any financial covenants. The Company may redeem the 2022 Senior Notes at any time prior to July 15, 2018 at a price equal to 100% of the aggregate principal amount so redeemed, plus accrued and unpaid interest, if any, to the redemption date and a make-whole premium set forth in the Indenture. The Company may also redeem up to 35% of the aggregate principal amount of the 2022 Senior Notes with the net cash proceeds of certain equity offerings at any time and from time to time before July 15, 2018, at a redemption price equal to 105.250% of the aggregate principal amount so redeemed, plus accrued and unpaid interest, if any, to the redemption date. The Company also has the option to redeem the 2022 Senior Notes on or after: July 15, 2018 through July 14, 2019 at 102.625% of par; July 15, 2019 through July 14, 2020 at 101.313% of par; and July 15, 2020 and thereafter at 100% of par. In addition, if the Company undergoes a change of control, as provided in the Indenture, the Company will be required to make an offer to purchase each holder’s 2022 Senior Notes at a price equal to 101% of their principal amount, plus accrued and unpaid interest, if any, to the repurchase date. The Company evaluated the 2022 Senior Notes for derivatives pursuant to ASC 815 and did not identify any embedded derivatives that require bifurcation. All features were deemed to be clearly and closely related to the host instrument. Convertible Notes On December 10, 2007, the Company issued and sold $1.725 billion , at par, of 2.00% Convertible Senior Notes due December 15, 2037 (“2007 Notes”). On November 18, 2010, the Company entered into separate, privately-negotiated exchange agreements under which it retired $450.0 million in aggregate principal of its 2007 Notes for $450.0 million in aggregate principal of new 2.00% Convertible Exchange Senior Notes due December 15, 2037 (“2010 Notes”). On February 29, 2012, the Company entered into separate, privately-negotiated exchange agreements under which it retired $500.0 million in aggregate principal of the 2007 Notes for $500.0 million in aggregate principal of new 2.00% Convertible Senior Notes due March 1, 2042 (“2012 Notes”). On February 14, 2013, the Company entered into separate, privately-negotiated exchange agreements under which it retired $370.0 million in aggregate principal of the 2007 Notes for $370.0 million in aggregate principal of new 2.00% Convertible Senior Notes due December 15, 2043 (“2013 Notes”). The remaining 2007 Notes were redeemed in fiscal 2014. On November 9, 2016, the Company announced that pursuant to the terms of the indenture for the 2010 Notes, holders of the 2010 Notes had the option of requiring the Company to repurchase their 2010 Notes on December 16, 2016 at a repurchase price payable in cash equal to 100% of the original principal amount of the 2010 Notes. None of the 2010 Notes were surrendered for repurchase pursuant to the option. In addition, the Company also announced on November 9, 2016 that, pursuant to the terms of the indenture, it had elected to redeem, on December 19, 2016, all of the then outstanding 2010 Notes at a redemption price payable in cash equal to 100% of the accreted principal amount of the 2010 Notes. Holders of the 2010 Notes also had a right to convert their 2010 Notes. During the first quarter of fiscal 2017, all of the outstanding 2010 Notes were either converted or surrendered for conversion in aggregate principal of $12.3 million , which was paid out over the first and second quarters of fiscal 2017. The payouts included an additional $8.7 million of premium payments due to the Company's stock price exceeding the conversion price. The 2012 Notes and the 2013 Notes are collectively referred to herein as the “Convertible Notes.” Holders may require the Company to repurchase the Convertible Notes prior to maturity on the dates set forth below: • the 2012 Notes on each of March 1, 2018, 2022, 2027 and 2032 and March 2, 2037; and • the 2013 Notes on each of December 15, 2017, 2022, 2027, 2032 and 2037. Holders may also require the Company to repurchase the Convertible Notes upon a fundamental change, as defined in each of the applicable indentures. The Company may redeem all or a portion of the 2012 Notes at any time on or after March 6, 2018 and all or a portion of the 2013 Notes at any time on or after December 15, 2017 . If, prior to maturity, a holder requires the Company to repurchase the Convertible Notes or the Company elects to redeem the Convertible Notes, the repurchase or redemption price of each Convertible Note will equal 100% of its principal amount, plus accrued and unpaid interest to, but excluding, the redemption or repurchase date, as applicable. On November 14, 2017, the Company announced that it would repurchase, on December 15, 2017, all of the outstanding 2013 Notes at a repurchase price in cash equal to 100% of the accreted principal amount of the 2013 Notes validly surrendered for repurchase and not withdrawn, at the option of the holders of the 2013 Notes. The Company also announced on November 14, 2017, that it had elected to redeem, on December 15, 2017, all of the outstanding 2013 Notes (those 2013 Notes not surrendered to us for repurchase on December 15, 2017 or validly submitted for conversion prior to December 15, 2017) at a redemption price equal to 100% of the accreted principal amount of the 2013 Notes to be redeemed. It is the Company's current intent and policy to settle any conversion of the Convertible Notes as if the Company had elected to make either a net share settlement or all cash election, such that upon conversion, the Company intends to pay the holders in cash for the principal amount of the Convertible Notes and, if applicable shares of its common stock or cash to satisfy the premium based on a calculated daily conversion value. The Company also announced on November 14, 2017 that as provided in the indenture for the 2013 Notes, it had made an irrevocable election to settle any conversion of the 2013 Notes validly submitted on or after November 14, 2017 in cash. The 2010 bore interest at 2.00% per year on the principal amount payable semi-annually through December 15, 2016. The 2012, and 2013 Notes originally bore interest at a rate of 2.00% per year on the principal amount payable semi-annually on March 1 and September 1, and June 15 and December 15, respectively, of each year ending on March 1, 2018 and December 15, 2013, respectively. The 2013 Notes no longer bear interest payable at 2.00% . The 2012 Notes will accrete principal from March 1, 2018 at a rate that provides holders with an aggregate annual yield to maturity of 2.00% per year. The 2013 Notes accrete principal from their date of issuance at a rate of 4.00% per year until and including December 15, 2017, and 2.00% per year thereafter. Beginning with the six month interest period commencing March 1, 2018 and December 15, 2017, the Company will pay contingent interest during any six month interest period to the holders of 2012 and 2013 Notes, respectively, if the “trading price”, as defined, of the 2012 and 2013 Notes for each of the five trading days ending on the second trading day immediately preceding the first day of the applicable six month interest period equals or exceeds 120% of the accreted principal amount of the 2012 and 2013 Notes. The holders of each of the 2012 or 2013 Notes may convert their respective Notes into shares of the Company’s common stock at a conversion price of approximately $31.175 per share and $38.59 per share, respectively, subject to adjustment, prior to the close of business on December 1, 2041 and September 15, 2043, respectively, subject to prior redemption or repurchase of the 2012, and 2013 Notes, respectively, under any of the following circumstances: (1) during any calendar quarter if the last reported sale price of the Company’s common stock exceeds 130% of the conversion price for at least 20 trading days in the 30 consecutive trading days ending on the last trading day of the preceding calendar quarter; (2) during the five business day period after any five consecutive trading day period in which the trading price per note for each day of such period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such day; (3) if the notes have been called for redemption; or (4) upon the occurrence of specified corporate events. At the option of the holder, regardless of the foregoing circumstances, holders may convert their respective 2012 and 2013 Notes at any time on or after December 1, 2041 and September 15, 2043, respectively, through the close of business on the second scheduled trading day immediately preceding the maturity date. The conversion rate will not be adjusted for accrued interest or accreted principal in excess of the original $1,000 principal amount, as accrued interest and accreted principal will not be convertible into common stock. For the 2013 Notes none of these triggering events have occurred as of September 30, 2017. On various dates during the fourth quarter of fiscal 2017, the Company entered into privately negotiated repurchase transactions and extinguished $17.9 million and $68.0 million principal amount of the 2012 Notes and 2013 Notes, respectively, for total payments of $23.1 million and $82.9 million , respectively. These amounts include the conversion premium resulting from the Company's stock price on the date of the transactions being in excess of the conversion prices of $31.175 and $38.59 , respectively, and on the 2013 Notes accreted principal of $13.3 million . Under ASC 470, these transactions were accounted for as an extinguishment and derecognition of the 2012 Notes and 2013 Notes and resulted in an aggregate debt loss extinguishment of $0.6 million . On various dates during the third quarter of fiscal 2017, the Company entered into privately negotiated repurchase transactions and extinguished $100.0 million principal amount of each of its 2012 Notes and 2013 Notes, for total payments of $269.1 million . This amount includes the conversion premium resulting from the Company's stock price on the date of the transactions being in excess of the conversion prices of $31.175 and $38.59 , respectively, and on the 2013 Notes accreted principal of $18.5 million . Under ASC 470, these transactions were accounted for as an extinguishment and derecognition of the 2012 Notes and 2013 Notes and resulted in an aggregate debt loss extinguishment of $2.6 million . On various dates during the fourth quarter of fiscal 2016, the Company entered into privately negotiated repurchase transactions and extinguished $46.3 million principal amount of the 2010 Notes for total payments of $79.2 million . These amounts include the conversion premium resulting from the Company's stock price on the date of the transactions being in excess of the conversion price of $23.03 for the 2010 Notes. Under ASC 470, these transactions were accounted for as an extinguishment and derecognition of the 2010 Notes and resulted in a debt loss extinguishment of $0.8 million . In addition, $1.3 million principal was put to the Company during the quarter. On various dates during the second quarter of fiscal 2016, the Company entered into privately negotiated repurchase transactions and extinguished $90.0 million and $136.6 million principal amount of the 2010 Notes and 2012 Notes, respectively, for total payments of $140.1 million and $171.3 million , respectively. These amounts include the conversion premium resulting from the Company's stock price on the date of the transactions being in excess of the conversion price of $23.03 and $31.175 for the 2010 Notes and 2012 Notes, respectively. Under ASC 470, these transactions were accounted for as an extinguishment and derecognition of the 2010 and 2012 Notes and resulted in an aggregate debt loss extinguishment of $4.5 million . On various dates during the fourth quarter of fiscal 2015, the Company entered into privately negotiated repurchase transactions and extinguished $300.0 million principal of the 2010 Notes for a total payment of $543.7 million , which includes the conversion premium resulting from the Company's stock price on the date of the transaction being in excess of the conversion price of $23.03 . Under ASC 470, this transaction was accounted for as an extinguishment and derecognition of the 2010 Notes and resulted in a debt loss extinguishment of $15.5 million . In lieu of delivery of shares of the Company’s common stock in satisfaction of the Company’s obligation upon conversion of the Convertible Notes, the Company may elect to deliver cash or a combination of cash and shares of its common stock. If the Company elects to satisfy its conversion obligation in a combination of cash and shares of the Company’s common stock, the Company is required to deliver up to a specified dollar amount of cash per $1,000 original principal amount of Convertible Notes, and will settle the remainder of its conversion obligation in shares of its common stock, in each case based on the daily conversion value calculated as provided in the respective indentures for the Convertible Notes. This net share settlement election is in the Company’s sole discretion and does not require the consent of holders of the Convertible Notes. It is the Company’s current intent and policy to settle any conversion of the Convertible Notes as if the Company had elected to make the net share settlement election. The Convertible Notes are the Company’s senior unsecured obligations and rank equally with all of its existing and future senior unsecured debt and prior to all future subordinated debt. The Convertible Notes are effectively subordinated to any future secured indebtedness to the extent of the collateral securing such indebtedness, and structurally subordinated to all indebtedness and other liabilities (including trade payables) of the Company’s subsidiaries. Accounting for the Convertible Notes The Convertible Notes have been recorded pursuant to FASB Staff Position (“FSP”) APB 14-1, Accounting for Convertible Debt Instruments That May Be Settled in Cash upon Conversion (Including Partial Cash Settlement) (FSP APB 14-1) (codified within ASC 470) since they can be settled in cash or partially in cash upon conversion. FSP APB 14-1 requires the liability and equity components of the convertible debt instrument to be separately accounted for in a manner that reflects the entity’s nonconvertible debt borrowing rate when interest expense is subsequently recognized. The excess of the debt’s principal amount over the amount allocated to the liability component is recognized as the value of the embedded conversion feature (“equity component”) within additional-paid-in capital in stockholders’ equity and amortized to interest expense over the expected life of the liability component (typically the date of the earliest redemption) using the effective interest method. The liability component is initially recorded at its fair value, which is calculated using a discounted cash flow technique. Key inputs used to estimate the fair value of the liability component included the Company’s estimated nonconvertible debt borrowing rate as of the measurement date (i.e., the date the Convertible Notes are issued), the amount and timing of cash flows, and the expected life of the Convertible Notes. The effective interest rate is estimated by comparing other companies’ debt issuances that had features similar to the Company’s debt excluding the conversion feature and who had similar credit ratings during the same annual period as the Company. In addition, third-party transaction costs are required to be allocated to the liability and equity components based on their relative values. The original issuance of the 2007 Notes and both exchange transactions for the 2010 Notes and 2012 Notes, which each included a derecognition and re-recognition, were accounted for under this accounting guidance. The 2013 Notes exchange transaction was accounted for as a modification pursuant to ASC 470-50 and not an extinguishment because the terms of the two debt instruments were not substantially different. The Company accounted for the 2012 Notes and 2013 Notes extinguishments in fiscal 2017, discussed above, under the derecognition provisions of subtopic ASC 470-20-40, which requires the allocations of the fair value of the consideration transferred and transaction costs incurred to the extinguishment of the liability component and the reacquisition of the equity component. In connection with these transactions, the Company recorded a debt extinguishment loss on the 2012 Notes of $0.9 million and a debt extinguishment loss on the 2013 Notes of $2.3 million , for a total debt extinguishment loss of $3.2 million in fiscal 2017. The loss on the debt was calculated as the difference between the fair value of the liability component immediately before the respective transactions and their related carrying values, which includes any debt discount and deferred issuance costs. The fair value of the liability component was calculated using a discounted cash flow technique and incorporates an estimated rate for non-convertible debt (with similar features as the 2012 and 2013 Notes excluding the conversion feature) issued by a company with a credit rating similar to the Company. In addition, under this accounting standard, a portion of the fair value of the consideration transferred is allocated to the reacquisition of the equity component, which is the difference

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company applies the provisions of ASC 820 for its financial assets and liabilities that are re-measured and reported at fair value each reporting period and its nonfinancial assets and liabilities that are re-measured and reported at fair value on a non-recurring basis. Fair value is the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining fair value, the Company considers the principal or most advantageous market in which it would transact and considers assumptions that market participants would use when pricing the asset or liability. Fair Value Hierarchy ASC 820 establishes a three-level valuation hierarchy for disclosure of fair value measurements. Financial assets and liabilities are categorized within the valuation hierarchy based upon the lowest level of input that is significant to the measurement of fair value. The three levels of the hierarchy are defined as follows: • Level 1—Inputs to the valuation methodology are quoted market prices for identical assets or liabilities. • Level 2—Inputs to the valuation methodology are other observable inputs, including quoted market prices for similar assets or liabilities and market-corroborated inputs. • Level 3—Inputs to the valuation methodology are unobservable inputs based on management’s best estimate of inputs market participants would use in pricing the asset or liability at the measurement date, including assumptions about risk. Assets/Liabilities Measured and Recorded at Fair Value on a Recurring Basis The Company has investments in publicly-traded companies, which are valued using quoted market prices, representing Level 1 assets, and investments in derivative instruments comprised of interest rate caps and forward foreign currency contracts, which are valued using analyses obtained from independent third party valuation specialists based on market observable inputs, representing Level 2 assets. The fair values of the Company's interest rate caps and forward foreign currency contracts represent the estimated amounts the Company would receive or pay to terminate the contracts. Refer to Note 2 for further discussion and information on the equity investments, the interest rate caps and forward foreign currency contracts. The Company has a payment obligation to the participants under its Nonqualified Deferred Compensation Plan (“DCP”). This liability is recorded at fair value based on the underlying value of certain hypothetical investments under the DCP as designated by each participant for their benefit. Since the value of the DCP obligation is based on market prices, the liability is classified within Level 1. Assets and liabilities measured and recorded at fair value on a recurring basis consisted of the following: Fair Value Measurements at September 30, 2017 Carrying Value Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Equity securities $ 0.1 $ 0.1 $ — $ — Interest rate caps - derivative 4.8 — 4.8 — Forward foreign currency contracts 0.4 — 0.4 — Total $ 5.3 $ 0.1 $ 5.2 $ — Liabilities: Deferred compensation liabilities $ 43.2 $ 43.2 $ — $ — Forward foreign currency contracts 4.0 — 4.0 — Total $ 47.2 $ 43.2 $ 4.0 $ — Fair Value Measurements at September 24, 2016 Carrying Value Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Equity securities $ 1.0 $ 1.0 $ — $ — Interest rate caps - derivative 1.4 — 1.4 — Forward foreign currency contracts 0.2 — 0.2 — Total $ 2.6 $ 1.0 $ 1.6 $ — Liabilities: Deferred compensation liabilities $ 37.0 $ 37.0 $ — $ — Forward foreign currency contracts 1.3 — 1.3 — Total $ 38.3 $ 37.0 $ 1.3 $ — There were no Level 3 assets or liabilities outstanding during fiscal 2017, 2016 and 2015. Assets Measured and Recorded at Fair Value on a Nonrecurring Basis The Company remeasures the fair value of certain assets and liabilities upon the occurrence of certain events. Such assets are comprised of cost-method equity investments and long-lived assets, including property, plant and equipment, intangible assets and goodwill. There were no impairments to assets measured using level 3 inputs in fiscal 2017, 2016 and 2015. Refer to Note 4 for disclosure of the nonrecurring fair value measurement related to the debt extinguishment losses recorded in fiscal 2017 , 2016 and 2015 . Disclosure of Fair Value of Financial Instruments The Company’s financial instruments mainly consist of cash and cash equivalents, accounts receivable, marketable securities, cost-method equity investments, interest rate caps, forward foreign currency contracts, insurance contracts, DCP liability, accounts payable and debt obligations. The carrying amounts of the Company’s cash and cash equivalents, accounts receivable and accounts payable approximate their fair value due to the short-term nature of these instruments. The Company’s marketable securities, interest rate caps, and forward foreign currency contracts are recorded at fair value. The carrying amount of the insurance contracts are recorded at the cash surrender value, as required by U.S. GAAP, which approximates fair value, and the related DCP liability is recorded at fair value. The Company believes the carrying amounts of its cost-method equity investments approximate fair value. Amounts outstanding under the Company’s Credit Agreement and Securitization Program of $1.67 billion and $200.0 million aggregate principal, respectively, as of September 30, 2017 are subject to variable rates of interest based on current market rates, and as such, the Company believes the carrying amount of these obligations approximates fair value. The Company’s 2022 Senior Notes had a fair value of approximately $1.05 billion and $1.06 billion as of September 30, 2017 and September 24, 2016 , respectively, based on their trading price, representing a Level 1 measurement. The fair value of the Company’s Convertible Notes is based on the trading prices of the respective notes and represents a Level 1 measurement. Refer to Note 4 for the carrying amounts of the various components of the Company’s debt. The estimated fair values of the Company’s Convertible Notes at September 30, 2017 and September 24, 2016 are as follows: 2017 2016 2010 Notes — 20.2 2012 Notes 297.3 481.9 2013 Notes 244.4 458.8 $ 541.7 $ 960.9

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company’s income before income taxes consisted of the following: Years ended September 30, 2017 September 24, 2016 September 26, 2015 Domestic $ 1,105.8 $ 310.7 $ 158.3 Foreign 124.7 104.6 18.9 $ 1,230.5 $ 415.3 $ 177.2 The provision for income taxes contained the following components: Years ended September 30, 2017 September 24, 2016 September 26, 2015 Federal: Current $ 701.1 $ 209.0 $ 185.2 Deferred (276.9 ) (122.7 ) (137.0 ) 424.2 86.3 48.2 State: Current 53.1 16.6 3.5 Deferred (15.9 ) (22.7 ) (11.0 ) 37.2 (6.1 ) (7.5 ) Foreign: Current 13.9 14.7 5.7 Deferred (0.3 ) (10.4 ) (0.8 ) 13.6 4.3 4.9 $ 475.0 $ 84.5 $ 45.6 The income tax provision differed from the tax provision computed at the U.S. federal statutory rate due to the following: Years ended September 30, 2017 September 24, 2016 September 26, 2015 Income tax provision at federal statutory rate 35.0 % 35.0 % 35.0 % Increase (decrease) in tax resulting from: Domestic production activities deduction (1.7 ) (5.0 ) (10.1 ) State income taxes, net of federal benefit 2.3 2.0 1.2 Non-deductible goodwill 9.2 — — Tax credits (0.8 ) (3.2 ) (3.8 ) Unrecognized tax benefits (1.4 ) 2.4 (1.8 ) Cumulative translation adjustment write-off — — 1.9 Compensation (0.5 ) 0.1 1.9 Foreign rate differential (2.6 ) (6.1 ) (1.6 ) Change in deferred tax rate 0.2 (1.8 ) — Change in valuation allowance (1.5 ) (3.4 ) 1.0 Other 0.4 0.3 2.1 38.6 % 20.3 % 25.8 % The Company's effective tax rate in fiscal 2017 was higher than the statutory rate primarily due to non-deductible goodwill related to the sale of the Blood Screening business, partially offset by the release of valuation allowances for capital losses utilized against the capital gain generated on the sale of the Blood Screening business, earnings in jurisdictions subject to lower tax rates, the domestic production activities deduction benefit, the release of uncertain tax positions due to statutes of limitations expirations and audit settlements, stock compensation benefits, and federal and state tax credits. The Company's effective tax rate in fiscal 2016 was lower than the statutory rate primarily due to earnings in jurisdictions subject to lower tax rates, the domestic production activities deduction benefit, and a change in the valuation allowance related to the sale of a marketable security with a higher tax than book basis. The Company's effective tax rate in fiscal 2015 was lower than the statutory rate primarily due to the domestic production activities deduction benefit. The Company uses the asset and liability method to account for income taxes in accordance with ASC 740, Income Taxes . Under this method, deferred income taxes are recognized for the future tax consequences of differences between the tax and financial accounting bases of assets and liabilities at each reporting period. Deferred income taxes are based on enacted tax laws and statutory tax rates applicable to the period in which these differences are expected to affect taxable income. A valuation allowance is established when necessary to reduce deferred tax assets to the amounts expected to be realized. The Company’s significant deferred tax assets and liabilities were as follows: September 30, 2017 September 24, 2016 Deferred tax assets Net operating loss carryforwards $ 50.1 $ 40.0 Capital losses 7.1 19.1 Non-deductible accruals 50.6 21.1 Non-deductible reserves 30.0 31.1 Stock-based compensation 39.3 34.8 Research and other credits 13.6 10.7 Nonqualified deferred compensation plan 16.4 14.1 Other temporary differences 16.5 9.2 223.6 180.1 Less: valuation allowance (28.2 ) (46.2 ) $ 195.4 $ 133.9 Deferred tax liabilities Depreciation and amortization $ (1,071.5 ) $ (1,030.8 ) Debt discounts and deferrals (88.4 ) (76.4 ) $ (1,159.9 ) $ (1,107.2 ) $ (964.5 ) $ (973.3 ) Under ASC 740, the Company can only recognize a deferred tax asset for the future benefit to the extent that it is “more likely than not” that these assets will be realized. After considering all available positive and negative evidence, the Company established a valuation allowance against specifically identified deferred tax assets because it is more-likely-than-not that these assets will not be realized. In making this determination, the Company considered numerous factors including historical profitability, estimated future taxable income and the character of such income. The valuation allowance decreased $18.0 million in fiscal 2017 from fiscal 2016 primarily due to capital loss utilization against the capital gain generated on the sale of the Blood Screening business. At September 30, 2017 , the Company had $64.3 million , $91.4 million and $36.5 million in gross federal, state, and foreign net operating losses, respectively, and $5.2 million , $10.3 million and $5.8 million in federal, state, and foreign credit carryforwards, respectively. These losses and credits expire between 2018 and 2037 , except for $33.7 million in losses and $2.2 million in credits that have unlimited carryforward periods. The federal, state, and foreign net operating losses exclude $4.5 million , $117.9 million and $45.4 million , respectively, in net operating losses, that the Company expects will expire unutilized. At September 30, 2017 , the Company had $90.3 million in gross unrecognized tax benefits excluding interest, of which $70.3 million , if recognized, would reduce the Company's effective tax rate. At September 24, 2016 , the Company had $163.6 million in gross unrecognized tax benefits excluding interest, of which $76.9 million , if recognized, would have reduced the Company's effective tax rate. The gross unrecognized tax benefits decreased by $73.3 million from fiscal 2016, of which $64.0 million was a balance sheet reclassification resulting from the effective settlement in fiscal 2017 of uncertain tax positions related to the convertible debt exchange that occurred in fiscal 2013 and $9.3 million was the net benefit recorded to the income tax provision primarily from audit settlements and expiring statutes of limitations partially offset by current year tax positions. In the next twelve months it is reasonably possible that the Company will reduce its gross unrecognized tax benefits by up to $2.0 million due to expiring statutes of limitations. The Company’s unrecognized income tax benefits activity for fiscal 2017 and 2016 was as follows: 2017 2016 Balance at beginning of fiscal year $ 163.6 $ 154.7 Tax positions related to current year: Additions 21.8 23.9 Reductions — — Tax positions related to prior years: Additions related to change in estimate 1.1 1.1 Reductions (77.3 ) (6.9 ) Payments (1.6 ) (6.0 ) Lapses in statutes of limitations (19.9 ) (3.2 ) Acquired tax positions: Additions related to reserves acquired from acquisitions 2.6 — Balance as of the end of the fiscal year $ 90.3 $ 163.6 The Company’s policy is to include accrued interest and penalties related to unrecognized tax benefits and income tax liabilities, when applicable, in income tax expense. As of September 30, 2017 and September 24, 2016 , gross accrued interest was $5.3 million and $13.1 million , respectively. At September 30, 2017 , no significant penalties have been accrued. The Company and its subsidiaries are subject to various federal, state, and foreign income taxes. The Company’s U.S. Federal income tax returns are generally no longer subject to examination prior to tax year 2014. During fiscal 2017, the Internal Revenue Service ("IRS") completed its audit for fiscal years 2013 and 2014. The Company made a cash payment of $1.7 million and recorded an income tax benefit of $10.9 million , including interest, related to the reversal of unrecognized tax benefits. State income tax returns are generally no longer subject to examination prior to fiscal year 2013. The Company is undergoing tax examinations in California (fiscal years 2011-2013), Massachusetts (fiscal years 2012-2013), and New York (fiscal years 2013-2015). The Company intends to reinvest, indefinitely, $309.5 million in unremitted foreign earnings. It is not practicable to estimate the additional taxes that may be payable upon repatriation.

Stockholders' Equity and Stock-

Stockholders' Equity and Stock-Based Compensation	12 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stockholders' Equity and Stock-Based Compensation	Stockholders' Equity and Stock-Based Compensation Stock Repurchase Program On November 11, 2013, the Company announced that its Board of Directors authorized the repurchase of up to $250 million of the Company’s outstanding common stock over a three -year period. During fiscal 2016, the Company repurchased 7.3 million shares of its common stock for total consideration of $250.0 million . This share repurchase authorization was fully utilized. On June 21, 2016, the Company's Board of Directors authorized the repurchase of up to an additional $500.0 million of the Company's outstanding common stock over the next five years . There were no repurchases of common stock made under this authorization during fiscal 2016. During fiscal 2017, the Company repurchased 5.3 million shares of its common stock for total consideration of $200.1 million . Stock-Based Compensation Equity Compensation Plans The Company has one share-based compensation plan pursuant to which awards are currently being issued—the 2008 amended and restated Equity Incentive Plan (“2008 Equity Plan”). The purpose of the 2008 Equity Plan is to provide stock options, restricted stock units and other equity interests in the Company to employees, officers, directors, consultants and advisors of the Company and any other person who is determined by the Board of Directors to have made (or is expected to make) contributions to the Company. The 2008 Equity Plan is administered by the Board of Directors of the Company, and a total of 31.5 million shares were reserved for issuance under this plan. As of September 30, 2017 , the Company had 6.8 million shares available for future grant under the 2008 Equity Plan. The following presents stock-based compensation expense in the Company’s Consolidated Statements of Operations in fiscal 2017 , 2016 and 2015 : 2017 2016 2015 Cost of revenues $ 10.7 $ 10.5 $ 8.7 Research and development 11.2 10.8 8.6 Selling and marketing 11.9 10.9 8.8 General and administrative 34.4 32.8 29.1 Restructuring and divestiture — 0.4 4.1 $ 68.2 $ 65.4 $ 59.3 Grant-Date Fair Value The Company uses a binomial model to determine the fair value of its stock options. The Company considers a number of factors to determine the fair value of options including the assistance of an outside valuation adviser. Information pertaining to stock options granted during fiscal 2017 , 2016 and 2015 and related assumptions are noted in the following table: Years ended September 30, 2017 September 24, 2016 September 26, 2015 Options granted (in millions) 1.0 1.1 1.3 Weighted-average exercise price $ 38.07 $ 39.32 $ 27.68 Weighted-average grant date fair value $ 12.33 $ 12.91 $ 9.95 Assumptions: Risk-free interest rates 1.8 % 1.6 % 1.7 % Expected life (in years) 4.7 4.7 5.3 Expected volatility 36.6 % 37.8 % 38.6 % Dividend yield — — — The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected life of the stock options. In projecting expected stock price volatility, the Company uses a combination of historical stock price volatility and implied volatility from observable market prices of similar equity instruments. The Company estimated the expected life of stock options based on historical experience using employee exercise and option expiration data. In connection with appointing Stephen P. MacMillan as its new President and Chief Executive Officer in December 2013, the Company granted approximately 0.1 million market stock units ("MSUs"). The MSUs vest in three separate tranches in an amount of 1/3 rd of the total amount of the award based on the Company’s stock price meeting certain defined average stock prices for 30 consecutive trading days. These MSUs were valued at an average of $18.65 per share using the Monte Carlo simulation model and each tranche had its own derived service period. The Company recognized compensation expense under the accelerated method as prescribed by ASC 718 in fiscal 2014 through a portion of fiscal 2015, and all tranches vested due to the defined average stock prices being met for the required period. In addition, per the terms of his employment agreement, the Company granted 0.2 million restricted stock units ("RSUs") to match Mr. MacMillan’s purchase of 0.2 million shares of the Company’s common stock on the open market in the second quarter of fiscal 2014. The RSUs cliff vest three years from the date of grant, and the Company accounted for this grant as a liability award pursuant to ASC 718 because this RSU award contained an additional vesting condition (the requirement that Mr. MacMillan retain the matching shares during the vesting period) that was not service, performance or market based. As such, this award was marked-to-market at each reporting period and vested during fiscal 2017 at which time the liability of $7.8 million was reclassified to additional paid-in-capital. Stock-Based Compensation Expense Attribution The Company uses the straight-line attribution method to recognize stock-based compensation expense for stock options and RSUs. The vesting term of stock options is generally four or five years with annual vesting of 25% and 20% per year, respectively, on the anniversary of the grant date, and RSUs generally vest over three or four years with annual vesting at 33% and 25% per year, respectively, on the anniversary of the grant date. Effective in the fourth quarter of fiscal 2016, the Company implemented a retirement provision providing for the continued vesting of equity awards granted after November 6, 2015 once an employee meets certain age and years of service criteria and retires from the Company. This provision from an accounting perspective may result in a shorter requisite service period for certain employees, resulting in accelerated stock-based compensation expense. Since this provision affected previously granted awards, it was accounted for as a modification and the Company recognized an additional $4.0 million of expense in the fourth quarter of fiscal 2016. The amount of stock-based compensation recognized during a period is based on the value of the portion of the awards that are ultimately expected to vest. ASC 718 requires forfeitures to be estimated at the time granted and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Based on an analysis of historical forfeitures, the Company has determined a specific forfeiture rate for certain employee groups and has applied forfeiture rates ranging from 0% to 7.0% as of September 30, 2017 depending on the specific employee group. This analysis is re-evaluated annually and the forfeiture rate will be adjusted as necessary. Ultimately, the actual stock-based compensation expense recognized will only be for those stock options and RSUs that vest. Stock-based compensation expense related to stock options was $12.2 million , $10.9 million , and $12.2 million in fiscal 2017 , 2016 and 2015 , respectively. Stock compensation expense related to stock units, including RSUs, performance stock units ("PSUs") and MSUs, was $51.6 million , $50.5 million , and $43.7 million in fiscal 2017 , 2016 and 2015 , respectively. The related tax benefit recorded in the Consolidated Statements of Income was $22.6 million , $23.1 million and $17.7 million in fiscal 2017, 2016 and 2015 , respectively. Included within stock-based compensation expense in fiscal 2016 and 2015 is $0.4 million and $4.1 million , respectively, related to modification accounting, the acceleration of vesting of certain retention RSUs provided under their original terms upon termination, and the acceleration of vesting for certain options assumed in the Gen-Probe acquisition related to employees who were terminated in connection with the Company’s restructuring action to consolidate its Diagnostics operations. The original terms of the stock options assumed in the Gen-Probe acquisition provided for acceleration upon a change-in-control and termination within 18 months of the change-in-control. At September 30, 2017 , there was $21.0 million and $54.6 million of unrecognized compensation expense related to stock options and RSUs, respectively, to be recognized over a weighted average period of 2.5 years and 1.8 years, respectively. Share Based Payment Activity The following table summarizes all stock option activity under the Company’s stock option plans for the year ended September 30, 2017 : Number of Shares (in millions) Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in Years) Aggregate Intrinsic Value (in millions) Options outstanding at September 24, 2016 6.1 $ 25.37 4.9 $ 80.1 Granted 1.0 38.07 Canceled/ forfeited (0.2 ) 30.59 Exercised (1.4 ) 23.25 $ 25.9 Options outstanding at September 30, 2017 5.5 $ 28.15 5.4 $ 50.3 Options exercisable at September 30, 2017 2.6 $ 23.31 3.6 $ 34.8 Options vested and expected to vest at September 30, 2017 (1) 5.4 $ 28.09 5.5 $ 50.0 (1) This represents the number of vested stock options as of September 30, 2017 plus the unvested outstanding options at September 30, 2017 expected to vest in the future, adjusted for estimated forfeitures. During fiscal 2016 and 2015 , the total intrinsic value of options exercised (i.e., the difference between the market price on the date of exercise and the price paid by the employee to exercise the options) was $21.6 million and $42.0 million , respectively. A summary of the Company’s RSU activity during the year ended September 30, 2017 is presented below: Non-vested Shares Number of Shares (in millions) Weighted-Average Grant-Date Fair Value Non-vested at September 24, 2016 2.8 $ 29.40 Granted 1.0 38.03 Vested (1.2 ) 27.43 Forfeited (0.3 ) 32.21 Non-vested at September 30, 2017 2.3 $ 34.06 The number of RSUs vested includes shares withheld on behalf of employees to satisfy minimum statutory tax withholding requirements. The Company pays the minimum statutory tax withholding requirement on behalf of its employees. During fiscal 2017 , 2016 and 2015 the total fair value of RSUs vested was $38.5 million , $28.4 million and $27.2 million , respectively. The Company also granted 0.2 million and 0.2 million and 0.3 million PSUs during fiscal 2017 , 2016 , and 2015, respectively, to members of the Company's senior management team, which have a weighted-average grant date fair value of $38.84 and $39.72 ,and 26.58 , respectively. Each recipient of the PSUs is eligible to receive between zero and 200% of the target number of shares of the Company’s common stock at the end of three year performance period provided the Company’s defined Return on Invested Capital metrics are achieved. These awards cliff-vest three years from the date of grant, and the Company is recognizing compensation expense ratably over the required service period based on its estimate of the number of shares will vest upon achieving the measurement criteria. If there is a change in the estimate of the number of shares that are probable of vesting, the Company will cumulatively adjust compensation expense in the period that the change in estimate is made. The Company also granted 0.1 million MSUs during fiscal 2017 to its senior management team. Each recipient of MSUs is eligible to receive between zero and 200% of the target number of shares of the Company’s common stock at the end of three year performance period based upon achieving a certain total shareholder return relative to a defined peer group. The MSUs were valued at $48.98 per share using the Monte Carlo simulation model. These awards cliff-vest three years from the date of grant, and the Company is recognizing compensation expense for the MSUs ratably over the service period. Employee Stock Purchase Plan In March 2012, the Company’s stockholders approved the Hologic, Inc. 2012 Employee Stock Purchase Plan (“2012 ESPP”), which provides for the granting of up to 2.5 million shares of the Company’s common stock to eligible employees. The 2012 ESPP plan period is semi-annual and allows participants to purchase the Company’s common stock at 85% of the lower of (i) the market value per share of the common stock on the first day of the offering period or (ii) the market value per share of the common stock on the purchase date. Stock-based compensation expense in fiscal 2017 , 2016 and 2015 was $4.4 million , $4.0 million and $3.4 million , respectively. The Company uses the Black-Scholes model to estimate the fair value of shares to be issued as of the grant date using the following weighted average assumptions: September 30, 2017 September 24, 2016 September 26, 2015 Assumptions: Risk-free interest rates 0.72 % 0.34 % 0.10 % Expected life (in years) 0.5 0.5 0.5 Expected volatility 24.9 % 27.2 % 27.4 % Dividend yield — — —

Profit Sharing 401(k) Plan

Profit Sharing 401(k) Plan	12 Months Ended
	Sep. 30, 2017
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Profit Sharing 401(k) Plan	Profit Sharing 401(k) Plan The Company has a qualified profit sharing plan covering substantially all of its employees. The Company made contributions of $20.2 million , $16.2 million and $14.4 million for fiscal 2017 , 2016 and 2015 , respectively.

Deferred Compensation Plan

Deferred Compensation Plan	12 Months Ended
	Sep. 30, 2017
Compensation Related Costs [Abstract]
Deferred Compensation Plan	Deferred Compensation Plans Nonqualified Deferred Compensation Plan Effective March 15, 2006, the Company adopted its DCP to provide non-qualified retirement benefits to a select group of executive officers, senior management and highly compensated employees of the Company. Eligible employees may elect to contribute up to 75% of their annual base salary and 100% of their annual bonus to the DCP and such employee contributions are 100% vested. In addition, the Company may elect to make annual discretionary contributions on behalf of participants in the DCP. Each Company contribution is subject to a three -year vesting schedule, such that each contribution vests one third annually. Employee contributions are recorded within accrued expenses. Upon enrollment into the DCP, employees make investment elections for both their voluntary contributions and discretionary contributions, if any, made by the Company. Earnings and losses on contributions based on these investment elections are recorded as a component of compensation expense in the period earned. Annually, the Compensation Committee of the Board of Directors has approved a discretionary cash contribution to the DCP for each year. Discretionary contributions by the Company to the DCP are held in a Rabbi Trust. The Company is recording compensation expense for the DCP discretionary contributions ratably over the three -year vesting period of each annual contribution, unless the participant meets the plan retirement provision of reaching a certain age and years of service criteria in which case the expense is accelerated to match the required service period to receive such benefit. Under the DCP, the Company recorded compensation expense related to Company contributions of $3.4 million , $3.1 million and $1.8 million in fiscal 2017 , 2016 and 2015 , respectively. The full amount of the discretionary contribution, net of forfeitures, along with employee deferrals is recorded within accrued expenses and totaled $43.2 million and $37.0 million at September 30, 2017 and September 24, 2016 , respectively. The Company has purchased Company-owned group life insurance contracts, in which both voluntary and discretionary Company DCP contributions are invested, to partially fund payment of the Company’s obligation to the DCP participants. The total amount invested at September 30, 2017 and September 24, 2016 was $41.0 million and $36.0 million , respectively. The values of these life insurance contracts are recorded in other long-term assets. Changes in the cash surrender value of life insurance contracts, which were not significant in fiscal 2017 , 2016 and 2015 , are recorded within other income (expense), net. Deferred Equity Plan Effective September 17, 2015, the Company adopted the Hologic, Inc. Deferred Equity Plan (the “DEP”). The DEP is designed to allow executives and non-employee Directors to accumulate Company stock in a tax-efficient manner to meet their long-term equity accumulation goals and shareholder ownership guidelines. Under the DEP, eligible participants may elect to defer the settlement of RSUs and PSUs granted under the 2008 Equity Plan until separation from service or separation from service plus a fixed number of years. Participants may defer settlement by vesting tranche. Although the equity will vest on schedule, if deferral of settlement is elected, no shares will be issued until the settlement date. The settlement date will be the earlier of death, disability, change in control of the Company or separation from service plus the number of years of deferral elected by the participant. While these shares upon vesting are not distributed to the individuals and are not outstanding, these shares will be included in basic weighted average shares outstanding used to calculate earnings per share.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Finance Lease Obligations The Company has two non-cancelable lease agreements for buildings that are primarily used for manufacturing. The Company was responsible for a significant portion of the construction costs, and in accordance with ASC 840, Leases, Subsection 40-15-5, the Company was deemed to be the owner of the respective buildings during the construction period. At the completion of the construction period, the Company reviewed the lease for potential sale-leaseback treatment in accordance with ASC 840, Subsection 40, Sale-Leaseback Transactions. Based on its analysis, the Company determined that the lease did not qualify for sale-leaseback treatment. Therefore, the building, leasehold improvements and associated liabilities remain on the Company’s financial statements throughout the lease term, and the building and leasehold improvements are being depreciated on a straight line basis over their estimated useful lives of 35 years. The Company recorded the fair market value of the buildings and land aggregating $28.3 million within property and equipment on its Consolidated Balance Sheets. Depreciation expense related to the buildings and land is recorded within depreciation in the Company's Consolidated Statements of Cash Flows. During fiscal 2016, the Company executed an amendment to one of the leases extending the term to 2024 , and a renewal option was removed. There were no other significant provisions to the terms of the lease agreement. At September 30, 2017 , the Company has recorded $3.2 million in accrued expenses and $34.1 million in other long-term liabilities related to these obligations. The current term of the leases is for a period of approximately 10 and 8 years, respectively, with the option to extend for one lease for two consecutive 5 -year terms and the other for one 5 -year term. Future minimum lease payments, including principal and interest, under these leases were as follows at September 30, 2017 : Fiscal 2018 $ 2.9 Fiscal 2019 1.2 Fiscal 2020 1.2 Fiscal 2021 1.2 Fiscal 2022 1.2 Thereafter 1.7 Total minimum payments 9.4 Less-amount representing interest (3.0 ) Total $ 6.4 As a result of the Cynosure acquisition, the Company has capital leases the for the buildings at its primary U.S. operating facility and certain equipment and vehicles with payments due through May 2028. Future minimum lease payments, including principal and interest, under these leases were as follows at September 30, 2017 : Fiscal 2018 $ 2.8 Fiscal 2019 2.8 Fiscal 2020 2.8 Fiscal 2021 2.9 Fiscal 2022 3.0 Thereafter 17.3 Total minimum lease payments $ 31.6 Less-amount representing interest (7.3 ) Present value of obligations under capital lease $ 24.3 Current portion of capital lease obligations 1.6 Capital lease obligations, net of current portion $ 22.7 Non-cancelable Purchase and Royalty Commitments The Company has certain non-cancelable purchase obligations primarily related to inventory purchases and diagnostics instruments, primarily Panther systems, and to a lesser extent other operating expense commitments. These obligations are not recorded in the Consolidated Balance Sheets. For reasons of quality assurance, sole source availability or cost effectiveness, certain key components and raw materials and instruments are available only from a sole supplier and the Company has certain long-term supply contracts to assure continuity of supply. At September 30, 2017 , purchase commitments are as follows: Fiscal 2018 $ 56.4 Fiscal 2019 4.7 Fiscal 2020 1.1 Fiscal 2021 1.1 Fiscal 2022 1.1 Total $ 64.4 Concentration of Suppliers The Company purchases certain components of its products from a single or small number of suppliers. A change in or loss of these suppliers could cause a delay in filling customer orders and a possible loss of sales, which could adversely affect results of operations; however, management believes that suitable replacement suppliers could be obtained in such an event. Operating Leases The Company conducts its operations in leased facilities under operating lease agreements that expire through fiscal 2035 . Substantially all of the Company’s lease agreements require the Company to maintain the facilities during the term of the lease and to pay all taxes, insurance, utilities and other costs associated with those facilities. The Company makes customary representations and warranties and agrees to certain financial covenants and indemnities. In the event the Company defaults on a lease, typically the landlord may terminate the lease, accelerate payments and collect liquidated damages. As of September 30, 2017 , the Company was not in default of any covenants contained in its lease agreements. Certain of the Company’s lease agreements provide for renewal options. Such renewal options are at rates similar to the current rates under the agreements. Future minimum lease payments under all of the Company’s operating leases at September 30, 2017 are as follows: Fiscal 2018 $ 20.9 Fiscal 2019 18.0 Fiscal 2020 15.2 Fiscal 2021 12.5 Fiscal 2022 11.4 Thereafter 27.0 Total $ 105.0 Rent expense, net of sublease income from these locations, was $19.3 million , $17.9 million , and $19.2 million for fiscal 2017 , 2016 and 2015 , respectively. The Company subleases a portion of a building it owns and some of its rented facilities and has received aggregate rental income of $2.3 million , $2.4 million and $2.0 million in fiscal 2017 , 2016 and 2015 , respectively, which has been recorded as an offset to rent expense. The future minimum annual rental income payments under these sublease agreements at September 30, 2017 are as follows: Fiscal 2018 $ 2.3 Fiscal 2019 2.3 Fiscal 2020 1.5 Fiscal 2021 0.4 Fiscal 2022 0.4 Thereafter 0.7 Total $ 7.6

Litigation and Related Matters

Litigation and Related Matters	12 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Litigation and Related Matters	Litigation and Related Matters On June 9, 2010, Smith & Nephew, Inc. ("Smith & Nephew") filed suit against Interlace Medical, Inc. ("Interlace"), which the Company acquired on January 6, 2011, in the United States District Court for the District of Massachusetts. The complaint alleged that the Interlace MyoSure hysteroscopic tissue removal device infringed U.S. patent 7,226,459 (the '459 patent). On November 22, 2011, Smith & Nephew filed suit against the Company in the United States District Court for the District of Massachusetts. The complaint alleged that use of the MyoSure tissue removal system infringed U.S. patent 8,061,359 (the '359 patent). Both complaints sought preliminary and permanent injunctive relief and unspecified damages. On September 4, 2012, following a two week trial, the jury returned a verdict of infringement of both the '459 and '359 patents and assessed damages of $4.0 million . A two-day bench trial regarding the Company’s assertion of inequitable conduct on the part of Smith & Nephew with regard to the '359 patent began on December 10, 2012 and oral arguments on the issue of inequitable conduct were presented on February 27, 2013. On June 27, 2013, the Court denied the Company’s motions related to inequitable conduct and allowed Smith & Nephew’s request for injunction, but ordered that enforcement of the injunction be stayed until final resolution, including appeal, of the current re-examinations of both patents at the United States Patent and Trademark Office (“USPTO”). The Court also rejected the jury’s damage award and ordered the parties to identify a mechanism for resolving the damages issue. The USPTO issued final decisions that the claims of the '459 and the '359 patents asserted as part of the litigation are not patentable, which decisions Smith & Nephew appealed to the U.S. Patent Trial and Appeal Board. In 2016, the U.S. Patent Trial and Appeal Board (i) affirmed the USPTO decision with respect to the '459 patent, holding that the claims at issue are invalid, and (ii) reversed the USPTO decision with respect to the '359 patent, holding that the claims at issue are not invalid. The Company and Smith & Nephew have appealed the decisions by the Patent Trial and Appeal Board on the '359 patent and the '459 patent, respectively, to the U.S. Court of Appeals for the Federal Circuit. Briefing on both appeals was completed on June 7, 2017. Oral argument on the ‘459 patent took place on October 4, 2017, and oral argument on the ‘359 patent is scheduled for December 7, 2017. At this time, based on available information regarding this litigation, the Company is unable to reasonably assess the ultimate outcome of this case or determine an estimate, or a range of estimates, of potential losses. On April 11, 2017, Minerva Surgical, Inc. (“Minerva”) filed suit against the Company and Cytyc Surgical Products, LLC (“Cytyc”) in the United States District Court for the Northern District of California alleging that the Company’s and Cytyc’s NovaSure ADVANCED endometrial ablation device infringes Minerva’s U.S. patent 9,186,208. Minerva is seeking a preliminary and permanent injunction against the Company and Cytyc from selling this NovaSure device as well as enhanced damages and interest, including lost profits, price erosion and/or royalty. A hearing on Minerva’s motion is scheduled for December 14, 2017. At this time, based on available information regarding this litigation, the Company is unable to reasonably assess the ultimate outcome of this case or determine an estimate, or a range of estimates, of potential losses. In January 2012, Enzo Life Sciences, Inc. ("Enzo") filed suit against the Company's subsidiary, Gen-Probe Incorporated ("Gen-Probe"), in the United States District Court for the District of Delaware, alleging that certain of Gen-Probe’s diagnostics products, including products that incorporate Gen-Probe’s hybridization protection assay technology (HPA), which include the Aptima line of products, infringe Enzo’s U.S. patent 6,992,180 (the '180 patent). On March 6, 2012, Enzo filed suit against the Company in the United States District Court for the District of Delaware, alleging that products based on the Company's Invader chemistry platform, such as Cervista HPV HR and Cervista HPV 16/18, infringe the '180 patent. On July 16, 2012, Enzo amended its complaint to include additional products that include HPA or TaqMan reagent chemistry, including the Progensa, AccuProbe and Prodesse product lines. The Company counter-claimed for non-infringement, invalidity and unenforceability of the '180 patent. On September 30, 2013, Enzo filed its infringement contentions which added products including "Torch" probes (e.g., MilliPROBE Real-Time Detection System for Mycoplasma), PACE and certain Procleix assays. Both complaints seek preliminary and permanent injunctive relief and unspecified damages. Enzo asserted the '180 patent claims against six other companies, three of which have settled with Enzo. Summary judgment and Daubert motions were filed by the parties on December 15, 2016. A hearing on the summary judgment motions was held on April 4, 2017, and on June 28, 2017, the Court ruled that the '180 patent is invalid for nonenablement. Final judgment was entered in the case on July 19, 2017, and on August 18, 2017, Enzo filed a notice of appeal with the Court of Appeals for the Federal Circuit. Enzo’s initial brief in support of its appeal is due on November 28, 2017. At this time, based on available information regarding this litigation, the Company is unable to reasonably assess the ultimate outcome of this case or determine an estimate, or a range of estimates, of potential losses. On March 27, 2015, Enzo filed an additional suit against the Company in the United States District Court for the District of Delaware. The complaint alleges that certain additional Company molecular diagnostic products, including, inter alia, the Procleix Parvo/HAV assays and coagulation products, including the Invader Factor II test and the Invader Factor V test, also infringe the '180 patent. The complaint further alleged that certain of the Company’s molecular diagnostic products, including the Company’s Progensa PCA3, Aptima and Procleix products using target capture technology infringe Enzo’s U. S. Patent 7,064,197 (the '197 patent). On June 11, 2015, this matter was stayed, and remains stayed, pending the resolution of summary judgment motions in other related suits involving the '197 patent. On March 30, 2016, Hologic filed two requests for inter partes review of the ‘197 patent at the USPTO. The USPTO instituted the two inter partes reviews on all challenged claims on October 4, 2016. Combined oral arguments for the two inter partes reviews were held on June 1, 2017. On September 28 and October 2, 2017, the PTAB issued final written decisions in the two inter partes reviews finding that all of the challenged claims of the’197 patent are unpatentable. Enzo will have an opportunity to appeal the decisions of the USPTO to the United States Court of Appeals for the Federal Circuit. At this time, based on available information regarding this litigation and the related inter partes reviews, the Company is unable to reasonably assess the ultimate outcome of this case or determine an estimate, or a range of estimates, of potential losses. On October 3, 2016, Enzo filed an additional suit against the Company in the United States District Court for the District of Delaware. The complaint alleges that all of the Company's Progensa PCA3, Aptima and Procleix products infringe U.S. Patent 6,221,581 (the '581 patent). On November 28, 2016, the Company filed an answer and counterclaims of non-infringement, invalidity and unenforceability. On June 30, 2017, Hologic filed its initial invalidity contentions, which provide support for finding that the asserted claims of the '581 patent are invalid based on anticipation, obviousness, lack of adequate written description and enablement, and indefiniteness. On August 31, 2017, the Company and Enzo filed supplemental invalidity charts and supplemental infringement charts, respectively. On October 4, 2017, the Company filed for inter partes review of the ‘581 patent with the USPTO based on Enzo’s asserted claims. A decision on whether to institute inter partes review is expected in April 2018. At this time, based on available information regarding this litigation and the related request for inter partes review, the Company is unable to reasonably assess the ultimate outcome of this case or determine an estimate, or a range of estimates, of potential losses. On February 3, 2017, bioMérieux, S.A. and bioMérieux, Inc. (collectively “bioMérieux”) filed suit against the Company in the United States District Court for the Middle District of North Carolina. The complaint alleges that the Company’s Aptima HIV-1 RNA Qualitative assay and Aptima HIV-1 Quant Dx assay, as well as products manufactured by the Company and sold to Grifols, S.A. and Grifols Diagnostic Solutions Inc. (“Grifols USA”) for resale under the names Procleix HIV-1/HCV assay, Procleix Ultrio assay, and Procleix Ultrio Plus assay, infringe U.S. Patent Nos. 8,697,352 and 9,074,262. On April 3, 2017, the Company and Grifols USA filed a motion to dismiss asking the Court to dismiss the complaint in its entirety for bioMérieux’s failure to state a claim upon which relief can be granted. On June 9, 2017, Hologic and Grifols USA filed a supplemental motion to dismiss for improper venue. bioMérieux filed a response to the venue motion on June 30, 2017, and Hologic and Grifols USA responded by filing a brief in further support of their motion to dismiss for improper venue on July 14, 2017. At this time, based on available information regarding this litigation, the Company is unable to reasonably assess the ultimate outcome of this case or determine an estimate, or range of estimates, of potential losses. On July 27, 2016, plaintiff ARcare, Inc., individually and as putative representative of a purported nationwide class, filed a complaint against Cynosure. The plaintiff alleges that Cynosure violated the Telephone Consumer Protection Act by: (i) sending fax advertisements that did not comply with statutory and Federal Communications Commission requirements that senders provide recipients with certain information about how to opt out from receiving faxed advertisements in the future; and (ii) sending unsolicited fax advertisements. The complaint sought damages, declaratory and injunctive relief, and attorneys’ fees on behalf of a purported class of all recipients of purported fax advertisements that the plaintiff alleges did not receive an adequate opt-out notice. On September 30, 2016, Cynosure answered the complaint and denied liability. On September 7, 2016, the plaintiff sent a demand letter seeking a class settlement for statutory damages under Massachusetts General Laws, Chapter 93A § 9 (“Chapter 93A”). On October 7, 2016, Cynosure responded denying any liability under Chapter 93A, but offering the plaintiff statutory damages of $25 on an individual basis. In March 2017, Cynosure and ARcare entered into a settlement agreement, subject to court approval, which requires Cynosure to pay settlement compensation of $8.5 million notwithstanding the number of claims filed. If approved, Cynosure would receive a full release from the settlement class concerning the conduct alleged in the complaint. A preliminary approval hearing was held on November 6, 2017. As a result of the settlement agreement, Cynosure recorded a charge of $9.2 million , in the period ended December 31, 2016, which was accrued on the Company's balance sheet as of September 30, 2017. On March 17, 2017, prior to the consummation of Hologic’s acquisition of Cynosure, Hologic received a written demand for appraisal from BlueMountain Capital Management LLC and its affiliates with respect to 1,200,000 shares of Cynosure (value of $79.2 million at $66.00 per share). On April 17, 2017, the shareholders filed a Petition for Appraisal of Stock in the Court of Chancery of the State of Delaware requesting appraisal and payment of the fair value of their shares. The Company filed a response on May 5, 2017. On August 30, 2017, the shareholders withdrew their Petition, and the matter is fully resolved. On March 17, 2017, a purported shareholder of Cynosure, Michael Guido, filed an action against Cynosure in the Court of Chancery of the State of Delaware pursuant to Section 220 of the Delaware General Corporation Law seeking the production of certain books and records, including books and records related to the acquisition of Cynosure by Hologic. The action follows Cynosure’s rejection of Mr. Guido’s demand for these books and records on the ground that he had not met the requirements of the statute. In addition to books and records, the complaint seeks reasonable attorneys’ fees. The Company filed an answer to the complaint on April 10, 2017. On June 29, 2017, the parties agreed to stay all proceedings in the action and to suspend all the current deadlines in an attempt to resolve the matter. Hologic has since provided certain board minutes and materials to plaintiff's counsel on a Rule 408 "settlement purposes only" basis, and plaintiff's counsel is evaluating whether or not they intend to continue to pursue the action. At this time, based on available information regarding this matter, the Company is unable to reasonably assess the ultimate outcome of this case or determine an estimate, or range of estimates, of potential losses. The Company is a party to various other legal proceedings and claims arising out of the ordinary course of its business. The Company believes that except for those matters described above there are no other proceedings or claims pending against it the ultimate resolution of which could have a material adverse effect on its financial condition or results of operations. In all cases, at each reporting period, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under ASC 450, Contingencies. Legal costs are expensed as incurred.

Disposition

Disposition	12 Months Ended
	Sep. 30, 2017
Disposal Groups, Including Discontinued Operations and Collaborative Agreement [Abstract]
Disposition	Disposition Blood Screening Business On December 14, 2016, the Company entered into a definitive agreement to sell the assets of its blood screening business to its long-time commercial partner, Grifols for a sales price of $1.85 billion in cash, subject to adjustment based on an estimated closing amount of inventory. The divestiture was completed on January 31, 2017, and the Company received $1.865 billion . The sale resulted in a gain of $899.7 million recorded in the second quarter of fiscal 2017 within operations in the Consolidated Statements of Income. As a result of this disposition and proceeds received, the Company recorded a tax obligation of $649.5 million , which was paid during fiscal 2017. Upon the closing of the transaction, the Company's existing collaboration agreement with Grifols terminated, and a new collaboration agreement was executed as part of this transaction pursuant to which the Company provides certain research and development services to Grifols. In addition, the Company agreed to provide transition services to Grifols over the next two to three years depending on the nature of the respective service, including the manufacture of inventory. The Company has also agreed to sell Panther instrumentation and certain supplies to Grifols as part of a long term supply agreement. In determining the accounting for the multiple elements of the overall arrangement, the Company allocated $13.1 million of the proceeds to these elements based on their estimated fair values. The Company determined this disposal does not qualify to be reported as a discontinued operation as the blood screening business was deemed not to be strategic to the Company and has not had and will not have a major effect on the Company's operations and financial results. Under the previous collaboration agreement, the Company performed research and development activities and manufacturing, while Grifols performed the commercial and distribution activities. The blood screening business was embedded within the Company's molecular diagnostics business, and the Company retains ownership and will continue to use the intellectual property for the underlying technology of its molecular diagnostics assays and instrumentation. Income from operations of the disposed business presented below represents the pretax profit of the business as it was operated prior to the date of disposition. The operating expenses include only those that were incurred directly by and were retained by the disposed business and are now incurred by Grifols. As noted above, the Company is performing a number of transition services and the financial impact from these services are not included in the amounts presented below and the Company is in effect serving as a contract manufacturer of assays for Grifols for a two to three year period. Income from operations of the disposed business for the years periods ended September 30, 2017 and September 24, 2016 was as follows: Twelve Months Ended September 30, 2017 September 24, 2016 Income from operations $ 45.8 $ 99.1 Under the long term supply agreement and transition services agreement to manufacture assays, subsequent to disposing the blood screening business, the Company recognized $44.0 million of revenue in fiscal 2017. Prior Collaboration Agreement with Grifols Under its prior collaboration agreement with Grifols, the Company manufactured blood screening products, while Grifols was responsible for marketing, sales and service of those products, which Grifols sold under its trademarks. The Company was entitled to recover 50% of its manufacturing costs incurred in connection with the collaboration and received a percentage of the blood screening assay revenue generated under the collaboration. The Company’s share of revenue from assays it sold to Grifols was 50% . The Company recognized product revenue, and collaborative research and license revenue, which is included within services and other revenues, under the prior collaboration agreement. The Company recognized revenue of $96.5 million , $235.4 million and $253.1 million under this collaboration agreement in fiscal 2017 , 2016 , and 2015 respectively.

Business Segments and Geographi

Business Segments and Geographic Information	12 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Business Segments and Geographic Information	Business Segments and Geographic Information The Company reports segment information in accordance with ASC 280, Segment Reporting. Operating segments are identified as components of an enterprise about which separate, discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions about how to allocate resources and assess performance. The Company’s chief operating decision maker is its chief executive officer, and the Company’s reportable segments have been identified based on the types of products manufactured and the end markets to which the products are sold. Each reportable segment generates revenue from either the sale of medical equipment and related services and/or sale of disposable supplies, primarily used for diagnostic testing and surgical procedures. The Company has five reportable segments: Diagnostics, Breast Health, Medical Aesthetics, GYN Surgical and Skeletal Health. Certain reportable segments represent an aggregation of operating units within each segment. The Company measures and evaluates its reportable segments based on segment revenues and operating income adjusted to exclude the effect of non-cash charges, such as intangible asset amortization expense, intangible asset impairment charges, transaction and integration expenses for acquisitions, restructuring, consolidation and divestiture charges, litigation charges, and other one-time or unusual items. Identifiable assets for the five reportable segments consist of inventories, intangible assets, goodwill, and property, plant and equipment. The Company fully allocates depreciation expense to its five reportable segments. The Company has presented all other identifiable assets as corporate assets. There were no intersegment revenues. Segment information for fiscal 2017 , 2016 , and 2015 was as follows: Years ended September 30, September 24, September 26, Total revenues: Diagnostics $ 1,197.1 $ 1,236.9 $ 1,211.8 Breast Health 1,138.3 1,112.8 1,063.4 Medical Aesthetics 207.5 — — GYN Surgical 427.1 393.1 335.8 Skeletal Health 88.8 89.9 94.0 $ 3,058.8 $ 2,832.7 $ 2,705.0 Operating income: Diagnostics $ 1,054.2 $ 126.0 $ 109.5 Breast Health 373.4 350.5 296.3 Medical Aesthetics (115.9 ) — — GYN Surgical 65.0 69.1 38.6 Skeletal Health (6.5 ) 3.0 10.7 $ 1,370.2 $ 548.6 $ 455.1 Depreciation and amortization: Diagnostics $ 278.9 $ 341.8 $ 358.7 Breast Health 19.7 22.6 28.6 Medical Aesthetics 54.2 — — GYN Surgical 95.7 99.9 102.7 Skeletal Health 0.7 1.1 1.4 $ 449.2 $ 465.4 $ 491.4 Capital expenditures: Diagnostics $ 50.9 $ 53.5 $ 55.6 Breast Health 12.0 10.6 12.8 Medical Aesthetics 7.3 — — GYN Surgical 15.2 17.7 9.5 Skeletal Health 1.2 0.4 0.4 Corporate 21.0 12.3 11.1 $ 107.6 $ 94.5 $ 89.4 September 30, September 24, September 26, Identifiable assets: Diagnostics $ 2,621.6 $ 3,771.9 $ 4,055.8 Breast Health 824.0 809.1 815.4 Medical Aesthetics 1,751.2 — — GYN Surgical 1,494.6 1,570.7 1,658.1 Skeletal Health 25.5 30.9 25.3 Corporate 1,262.7 1,134.4 1,087.9 $ 7,979.6 $ 7,317.0 $ 7,642.5 The Company operates in the following major geographic areas as noted in the below chart. Revenue data is based upon customer location. Other than the United States, no single country accounted for more than 10% of consolidated revenues. The Company’s sales in Europe are predominantly derived from France, the United Kingdom and Germany. The Company’s sales in Asia-Pacific are predominantly derived from China, Australia and Japan. The “Rest of world” designation includes Canada, Latin America and the Middle East. Revenues by geography as a percentage of total revenues were as follows: Years ended September 30, September 24, September 26, United States 77.6 % 78.9 % 76.0 % Europe 10.0 % 10.2 % 11.8 % Asia-Pacific 8.1 % 7.6 % 8.5 % Rest of world 4.3 % 3.3 % 3.7 % 100.0 % 100.0 % 100.0 % The Company’s property, plant and equipment, net are geographically located as follows: September 30, 2017 September 24, 2016 September 26, 2015 United States $ 386.5 $ 370.7 $ 369.1 Costa Rica 30.1 28.1 27.7 Europe 57.1 49.2 50.8 Rest of world 17.5 12.2 9.5 $ 491.2 $ 460.2 $ 457.1

Accrued Expenses and Other Long

Accrued Expenses and Other Long-Term Liabilities	12 Months Ended
	Sep. 30, 2017
Payables and Accruals [Abstract]
Accrued Expenses and Other Long-Term Liabilities	Accrued Expenses and Other Long-Term Liabilities Accrued expenses and other long-term liabilities consisted of the following: September 30, 2017 September 24, 2016 Accrued Expenses Compensation and employee benefits $ 176.7 $ 176.4 Income and other taxes 66.9 38.4 Other 131.7 72.8 $ 375.3 $ 287.6 September 30, 2017 September 24, 2016 Other Long-Term Liabilities Reserve for income tax uncertainties $ 88.3 $ 167.6 Accrued lease obligation—long-term 34.1 34.8 Pension liabilities 10.0 11.2 Other 7.8 10.9 $ 140.2 $ 224.5

Pension and Other Employee Bene

Pension and Other Employee Benefits	12 Months Ended
	Sep. 30, 2017
Compensation and Retirement Disclosure [Abstract]
Pension and Other Employee Benefits	Pension and Other Employee Benefits The Company has certain defined benefit pension plans covering the employees of its Hitec Imaging German subsidiary (the “Pension Benefits”). As of September 30, 2017 and September 24, 2016 , the Company’s pension liability was $9.9 million and $11.0 million , respectively, which is primarily recorded as a component of long-term liabilities in the Consolidated Balance Sheets. Under German law, there are no rules governing investment or statutory supervision of the pension plan. As such, there is no minimum funding requirement imposed on employers. Pension benefits are safeguarded by the Pension Guaranty Fund, a form of compulsory reinsurance that guarantees an employee will receive vested pension benefits in the event of insolvency. The pension plans were closed on December 31, 1997 and only eligible employees at that date could participate in the plans prior to closing to new participants. The tables below provide a reconciliation of benefit obligations, plan assets, funded status, and related actuarial assumptions of the Company’s German Pension Benefits. Change in Benefit Obligation Years ended September 30, 2017 September 24, 2016 September 26, 2015 Benefit obligation at beginning of year $ (11.0 ) $ (10.0 ) $ (10.3 ) Service cost — — — Interest cost (0.1 ) (0.2 ) (0.3 ) Plan participants’ contributions — — — Actuarial gain (loss) 1.5 (1.2 ) (0.9 ) Foreign exchange gain (0.6 ) 0.1 1.2 Benefits paid 0.3 0.3 0.3 Benefit obligation at end of year (9.9 ) (11.0 ) (10.0 ) Plan assets — — — Benefit obligation at end of year $ (9.9 ) $ (11.0 ) $ (10.0 ) The tables below outline the components of the net periodic benefit cost and related actuarial assumptions of the Company’s German Pension Benefits. Components of Net Periodic Benefit Cost Years ended September 30, 2017 September 24, 2016 September 26, 2015 Service cost $ — $ — $ — Interest cost 0.1 0.4 0.3 Expected return on plan assets — — — Amortization of prior service cost — — Recognized net actuarial gain 0.4 (0.2 ) — Net periodic benefit cost $ 0.5 $ 0.2 $ 0.3 Weighted-Average Net Periodic Benefit Cost Assumptions 2017 2016 2015 Discount rate 2.15 % 1.30 % 2.05 % Expected return on plan assets — % — % — % Rate of compensation increase — % — % — % The projected benefit obligation for the German Pension Benefits with projected benefit obligations in excess of plan assets was $9.9 million and $11.0 million at September 30, 2017 and September 24, 2016 , respectively, and the accumulated benefit obligation for the German Pension Benefits was $9.9 million and $11.0 million at September 30, 2017 and September 24, 2016 , respectively. The Company is also obligated to pay long-term service award benefits under the German Pension Benefits. The projected benefit obligation for long-term service awards was $0.1 million at both September 30, 2017 and September 24, 2016 , respectively. The table below reflects the total Pension Benefits expected to be paid for the German Pension Benefits each fiscal year as of September 30, 2017 : 2018 $ 0.4 2019 $ 0.4 2020 $ 0.4 2021 $ 0.4 2022 $ 0.4 2023 to 2027 $ 2.2 The Company also maintains additional contractual pension benefits for its top German executive officers in the form of a defined contribution plan. These contributions were insignificant in fiscal 2017 , 2016 and 2015 . Additionally, the Company has Swiss pension plans, which were insignificant in fiscal 2017 , 2016 , and 2015 .

Quarterly Statement of Operatio

Quarterly Statement of Operations Information (Unaudited)	12 Months Ended
	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Statement of Operations Information (Unaudited)	Quarterly Statement of Operations Information (Unaudited) The following table presents a summary of quarterly results of operations for fiscal 2017 and 2016 : 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenue $ 734.4 $ 715.4 $ 806.1 $ 802.9 Gross profit 404.8 388.7 409.6 417.9 Net income (1) 86.5 526.8 59.5 82.7 Diluted net income per common share $ 0.30 $ 1.84 $ 0.21 $ 0.29 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenue $ 695.2 $ 693.3 $ 717.4 $ 726.8 Gross profit 379.1 385.0 393.1 406.1 Net income (2) 84.9 68.9 84.8 92.2 Diluted net income per common share $ 0.29 $ 0.24 $ 0.30 $ 0.33 (1) Net income in the first quarter of fiscal 2017 included restructuring charges of $3.2 million and acquisition charges of $2.6 million . Net income in the second quarter of fiscal 2017 included a gain on the sale of the blood screening business of $899.7 million , acquisition charges of $19.4 million , and restructuring charges of $1.6 million . Net income in the third quarter of fiscal 2017 included restructuring charges of $6.0 million and a debt extinguishment loss of $2.6 million . Net income in the fourth quarter of fiscal 2017 included restructuring charges of $2.5 million , and gain on sale of cost method investment of $2.0 million . (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.

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. The Company’s fiscal year ends on the last Saturday in September. Fiscal 2017 , 2016 and 2015 ended on September 30, 2017 , September 24, 2016 and September 26, 2015 , respectively.
Management's Estimates	Management’s Estimates and Uncertainties The preparation of financial statements in conformity with U.S. generally accepted accounting principles ("GAAP") requires management to make significant estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. Significant estimates and assumptions by management affect the Company’s revenue recognition for multiple element arrangements, allowance for doubtful accounts, the net realizable value of inventory, estimated fair value of cost-method equity investments, valuations, purchase price allocations and contingent consideration related to business combinations, expected future cash flows including growth rates, discount rates, terminal values and other assumptions and estimates used to evaluate the recoverability of long-lived assets and goodwill, estimated fair values of intangible assets and goodwill, amortization methods and periods, warranty reserves, certain accrued expenses, restructuring and other related charges, stock-based compensation, contingent liabilities, tax reserves, deferred tax rates and recoverability of the Company’s net deferred tax assets and related valuation allowances. Although the Company regularly assesses these estimates, actual results could differ materially from these estimates. Changes in estimates are recorded in the period in which they become known. The Company bases its estimates on historical experience and various other assumptions that it believes to be reasonable under the circumstances. The Company is subject to a number of risks similar to those of other companies of similar size in its industry, including dependence on third-party reimbursements to support the markets of the Company’s products, early stage of development of certain products, rapid technological changes, recoverability of long-lived assets (including intangible assets and goodwill), competition, stability of world financial markets, ability to obtain regulatory approvals, changes in the regulatory environment, limited number of suppliers, customer concentration, integration of acquisitions, substantial indebtedness, government regulations, management of international activities, protection of proprietary rights, patent and other litigation, dependence on contract manufacturers and dependence on key individuals.
Cash Equivalents	Cash Equivalents Cash equivalents are highly liquid investments with insignificant interest rate risk and maturities of three months or less at the time of acquisition.
Marketable Securities	Marketable Securities The Company’s marketable securities as of September 30, 2017 and September 24, 2016 are comprised solely of equity securities and as of September 26, 2015 also included mutual funds. The equity securities are investments in the common stock of publicly traded companies, and the mutual funds were used to fund a portion of the Company's deferred compensation plan. The equity securities are classified as available-for-sale and are recorded at fair value with the unrealized gains or losses, net of tax, recorded within accumulated other comprehensive income (loss), which is a component of stockholders’ equity. The mutual funds were classified as trading and recorded at fair value with unrealized gains and losses recorded in other income (expense), net in the Consolidated Statements of Income. The Company periodically reviews its marketable equity securities classified as available-for-sale for other-than-temporary declines in fair value below carrying value, or whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. The determination that a decline is other-than-temporary is, in part, subjective and influenced by many factors. When assessing marketable equity securities for other-than-temporary declines in fair value, the Company considers factors including: the significance of the decline in value compared to the carrying value; the underlying factors contributing to a decline in the price of the security; how long the market value of the investment has been less than its carrying value; any market conditions that impact liquidity; the views of external investment analysts; the financial condition and near-term prospects of the investee; any news or financial information that has been released specific to the investee; and the outlook for the overall industry in which the investee operates.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that subject the Company to credit risk primarily consist of cash and cash equivalents, cost-method equity investments, and trade accounts receivable. The Company invests its cash and cash equivalents with high credit quality financial institutions. The Company’s customers are principally located in the United States, Europe and Asia. The Company performs ongoing credit evaluations of the financial condition of its customers and generally does not require collateral. Although the Company is directly affected by the overall financial condition of the healthcare industry, as well as global economic conditions, management does not believe significant credit risk exists as of September 30, 2017 . The Company generally has not experienced any material losses related to receivables from individual customers or groups of customers in the healthcare industry. The Company maintains an allowance for doubtful accounts based on accounts past due and historical collection experience.
Inventories	Inventories Inventories are valued at the lower of cost or market on a first in, first out basis. Work-in-process and finished goods inventories consist of materials, labor and manufacturing overhead. The valuation of inventory requires management to estimate excess and obsolete inventory. The Company employs a variety of methodologies to determine the net realizable value of its inventory. Provisions for excess and obsolete inventory are primarily based on management’s estimates of forecasted sales, usage levels and expiration dates, as applicable for disposable products. A significant change in the timing or level of demand for the Company’s products compared to forecasted amounts may result in recording additional charges for excess and obsolete inventory in the future. The Company records charges for excess and obsolete inventory within cost of product revenues.
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment is recorded at cost less allowances for depreciation. The straight-line method of depreciation is used for all property and equipment. Property, plant and equipment consisted of the following: September 30, 2017 September 24, 2016 Equipment and software $ 422.4 $ 381.9 Equipment under customer usage agreements 368.7 334.6 Buildings and improvements 172.0 186.1 Leasehold improvements 60.6 65.6 Land 46.3 51.9 Furniture and fixtures 20.8 18.4 1,090.8 1,038.5 Less - accumulated depreciation and amortization (599.6 ) (578.3 ) $ 491.2 $ 460.2 Property, plant and equipment are depreciated over the following estimated useful lives: Asset Classification Estimated Useful Life Building and improvements 20–35 years Equipment and software 3–10 years Equipment under customer usage agreements 3–8 years Furniture and fixtures 5–7 years Leasehold improvements Shorter of the Original Term of Lease or Estimated Useful Life Equipment under customer usage agreements primarily consists of diagnostic instrumentation and imaging equipment located at customer sites but owned by the Company. Generally, the customer has the right to use the equipment for a period of time provided they meet certain agreed to conditions. The Company recovers the cost of providing the equipment from the sale of disposables. The depreciation costs associated with equipment under customer usage agreements are charged to cost of product revenues over the estimated useful life of the equipment. The costs to maintain the equipment in the field are charged to cost of product revenue as incurred.
Long-Lived Assets	Long-Lived Assets The Company reviews its long-lived assets, which includes property, plant and equipment and identifiable intangible assets (see below for discussion of intangible assets), for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable in accordance with ASC 360-10-35-15, Property, Plant and Equipment—Impairment or Disposal of Long-Lived Assets (ASC 360). Recoverability of these assets is evaluated by comparing the carrying value of the assets to the undiscounted cash flows estimated to be generated by those assets over their remaining economic life. If the undiscounted cash flows are not sufficient to recover the carrying value of the assets, the assets are considered impaired. The impairment loss is measured by comparing the fair value of the assets to their carrying value. Fair value is determined by either a quoted market price, if any, or a value determined by a discounted cash flow technique.
Business Combinations and Acquisition of Intangible Assets	Business Combinations and Acquisition of Intangible Assets The Company accounts for the acquisition of a business in accordance with ASC 805, Business Combinations (ASC 805). Amounts paid for each acquisition are allocated to the assets acquired and liabilities assumed based on their fair values at the date of acquisition. The Company determines the fair value of acquired intangible assets based on detailed valuations that use certain information and assumptions provided by management. The Company allocates any excess purchase price over the fair value of the net tangible and intangible assets acquired to goodwill. The Company uses the income approach to determine the fair value of developed technology and in-process research and development ("IPR&D") acquired in a business combination. This approach determines fair value by estimating the after-tax cash flows attributable to the respective asset over its useful life and then discounting these after-tax cash flows back to a present value. The Company bases its revenue assumptions on estimates of relevant market sizes, expected market growth rates, expected trends in technology and expected product introductions by competitors. Developed technology represents patented and unpatented technology and know-how. The value of the in-process projects is based on projects’ stage of completion, the complexity of the work completed as of the acquisition date, the projected costs to complete, the contribution of core technologies and other acquired assets, the expected introduction date, the estimated cash flows to be generated upon commercial release and the estimated useful life of the technology. The Company believes that the estimated developed technology and IPR&D amounts represent the fair value at the date of acquisition and do not exceed the amount a third-party would pay for the assets. The Company also uses the income approach, as described above, to determine the estimated fair value of certain other identifiable intangible assets including customer relationships, distribution agreements, trade names and business licenses. Customer relationships represent established relationships with customers, which provide a ready channel for the sale of additional products and services. Trade names represent acquired company and product names, and distribution agreements generally pertain to exclusive distribution of certain products manufactured by third parties
Intangible Assets and Goodwill	Intangible Assets and Goodwill Intangible Assets Intangible assets are initially recorded at fair value and stated net of accumulated amortization and impairments. The Company amortizes its intangible assets that have finite lives using either the straight-line method, or if reliably determinable, based on the pattern in which the economic benefit of the asset is expected to be utilized. Amortization is recorded over the estimated useful lives ranging from 2 to 30 years. The Company evaluates the realizability of its definite lived intangible assets whenever events or changes in circumstances or business conditions indicate that the carrying value of these assets may not be recoverable based on expectations of future undiscounted cash flows for each asset group. If the carrying value of an asset or asset group exceeds its undiscounted cash flows, the Company estimates the fair value of the assets, generally utilizing a discounted cash flow analysis based on the present value of estimated future cash flows to be generated by the assets using a risk-adjusted discount rate. To estimate the fair value of the assets, the Company uses market participant assumptions pursuant to ASC 820, Fair Value Measurements . Indefinite lived intangible assets, such as IPR&D assets, are required to be tested for impairment annually, or more frequently if indicators of impairment are present. The Company’s annual impairment test date is as of the first day of its fourth quarter. Intangible assets consisted of the following: September 30, 2017 September 24, 2016 Description Gross Carrying Value Accumulated Amortization Gross Carrying Value Accumulated Amortization Developed technology $ 4,528.7 $ 2,186.8 $ 3,983.7 $ 1,991.6 In-process research and development 46.0 — 3.7 — Customer relationships 552.8 393.8 1,098.9 546.2 Trade names 310.3 156.4 236.2 141.6 Distribution agreement 42.0 2.8 — — Non-competition agreements 1.5 0.1 — — Business licenses 2.4 2.2 2.4 2.1 $ 5,483.7 $ 2,742.1 $ 5,324.9 $ 2,681.5 During the second quarter of fiscal 2017, the Company divested its blood screening business and net book value of $154.0 million of developed technology and $387.7 million of customer relationship assets were disposed of (see Note 13). In addition, in the second quarter of fiscal 2017, the Company acquired Cynosure and recorded an aggregate of $994.0 million of intangible assets (see Note 3). In the third quarter of fiscal 2017, the Company acquired Medicor and recorded $5.4 million of intangible assets. In addition, during the third quarter of fiscal 2017, the Company obtained CE approval for its last in-process research and development project acquired in the Gen-Probe Incorporated acquisition and transferred $3.7 million to developed technology. In the third quarter of fiscal 2016, the Company accelerated the amortization of the Cystic Fibrosis developed technology asset of $6.2 million as a result of discontinuing this product line. In the second quarter of fiscal 2016, the Company acquired certain intellectual property for $4.8 million , which was recorded in developed technology. Amortization expense related to developed technology is classified as a component of cost of product revenues—amortization of intangible assets. Amortization expense related to customer relationships and contracts, trade names, and business licenses is classified as a component of amortization of intangible assets within operating expenses. The estimated amortization expense at September 30, 2017 for each of the five succeeding fiscal years was as follows: Fiscal 2018 $ 376.6 Fiscal 2019 $ 364.9 Fiscal 2020 $ 353.6 Fiscal 2021 $ 332.2 Fiscal 2022 $ 319.8 Goodwill In accordance with ASC 350, Intangibles—Goodwill and Other (ASC 350), the Company tests goodwill for impairment annually at the reporting unit level and between annual tests if events and circumstances indicate it is more likely than not that the fair value of a reporting unit is less than its carrying value. Events that could indicate impairment and trigger an interim impairment assessment include, but are not limited to, current economic and market conditions, including a decline in market capitalization, a significant adverse change in legal factors, business climate, operational performance of the business or key personnel, and an adverse action or assessment by a regulator. In performing the impairment test, the Company utilizes the two-step approach prescribed under ASC 350. The first step requires a comparison of the carrying value of each reporting unit to its estimated fair value. To estimate the fair value of its reporting units for Step 1, the Company primarily utilizes the income approach. The income approach is based on a DCF analysis and calculates the fair value by estimating the after-tax cash flows attributable to a reporting unit and then discounting the after-tax cash flows to present value using a risk-adjusted discount rate. Assumptions used in the DCF require significant judgment, including judgment about appropriate discount rates and terminal values, growth rates, and the amount and timing of expected future cash flows. The forecasted cash flows are based on the Company’s most recent budget and strategic plan and for years beyond this period, the Company’s estimates are based on assumed growth rates expected as of the measurement date. The Company believes its assumptions are consistent with the plans and estimates used to manage the underlying businesses. The discount rates used are intended to reflect the risks inherent in future cash flow projections and are based on estimates of the weighted-average cost of capital (“WACC”) of market participants relative to each respective reporting unit. The market approach considers comparable market data based on multiples of revenue or earnings before interest, taxes, depreciation and amortization (“EBITDA”) and is primarily used as a corroborative analysis to the results of the DCF analysis. The Company believes its assumptions used to determine the fair value of its reporting units are reasonable. If different assumptions were used, particularly with respect to forecasted cash flows, terminal values, WACCs, or market multiples, different estimates of fair value may result and there could be the potential that an impairment charge could result. Actual operating results and the related cash flows of the reporting units could differ from the estimated operating results and related cash flows. If the carrying value of a reporting unit exceeds its estimated fair value, the Company is required to perform the second step of the goodwill impairment test to measure the amount of impairment loss, if any. The second step of the goodwill impairment test compares the implied fair value of a reporting unit’s goodwill to its carrying value. The implied fair value of goodwill is derived by performing a hypothetical purchase price allocation for the impaired reporting unit as of the measurement date and allocating the reporting unit’s estimated fair value to its assets and liabilities. The residual amount from performing this allocation represents the implied fair value of goodwill. To the extent this amount is below the carrying value of goodwill, an impairment charge is recorded. The Company conducted its fiscal 2017 impairment test on the first day of the fourth quarter, and as noted above used DCF and market approaches to estimate the fair value of its reporting units as of July 2, 2017, and ultimately used the fair value determined by the DCF approach in making its impairment test conclusions. The Company believes it used reasonable estimates and assumptions about future revenue, cost projections, cash flows, market multiples and discount rates as of the measurement date. As a result of completing Step 1, all of the Company's reporting units had fair values exceeding their carrying values, and as such, Step 2 of the impairment test was not required. For illustrative purposes, had the fair value of each of the reporting units been lower by 10% , all of the reporting units, except the Company's Medical Aesthetics reporting unit, would still have passed Step 1 of the goodwill impairment test. This reporting unit had a fair value as of the measurement date that exceeded its carrying value by 2% with goodwill of $683.5 million . The Company acquired Cynosure, which is the sole business in Medical Aesthetics, on March 22, 2017. In connection with the Company's annual strategic planning process and annual goodwill impairment test, it lowered its estimated financial projections for this business as a result of its current operating performance being below expectations, which the Company primarily attributes to the significant turnover in the U.S. sales force in 2017. In the event, future operating performance is below forecasted projections, or there are negative changes to long-term growth rates or if discount rates increase, these factors could result in a decline in the fair value of the reporting unit and the Company may be required to record a goodwill impairment charge. At September 30, 2017 , the Company believes that its other reporting units, with goodwill aggregating $2.49 billion , was not at risk of failing Step 1 of the goodwill impairment test based on the current forecasts. The Company conducted its fiscal 2016 and 2015 impairment tests on the first day of the respective year's fourth quarter, and as noted above used DCF and market approaches to estimate the fair value of its reporting units as of June 26, 2016 and June 28, 2015, respectively, and ultimately used the fair value determined by the DCF approach in making its impairment test conclusions. As a result of completing Step 1, all of the Company's reporting units had fair values exceeding their carrying values, and as such, Step 2 of the impairment test was not required.
Other Assets	Other Assets Other assets consisted of the following: September 30, 2017 September 24, 2016 Other Assets Life insurance contracts $ 41.0 $ 36.0 Capitalized software 12.3 10.0 Manufacturing access fees 7.1 9.6 Cost-method equity investments 3.0 3.5 Deferred tax assets 9.1 9.3 Other 24.5 15.3 $ 97.0 $ 83.7 Life insurance contracts were purchased in connection with the Company’s Nonqualified Deferred Compensation Plan (“DCP”) and are recorded at their cash surrender value (see Note 9 for further discussion). Capitalized software relates to development costs incurred related to software embedded in the Company's products. The manufacturing access fees are related to a manufacturing supply and purchase agreement for our Aptima HPV products and are being amortized over the term of the agreement.
Research and Software Development Costs	Research and Software Development Costs Costs incurred for the research and development of the Company’s products are expensed as incurred. Nonrefundable advance payments for goods or services to be received in the future by the Company for use in research and development activities are deferred. The deferred costs are expensed as the related goods are delivered or the services are performed. The Company accounts for the development costs of software embedded in the Company’s products in accordance with ASC 985, Software. Costs incurred in the research, design and development of software embedded in products to be sold to customers are charged to expense until technological feasibility of the ultimate product to be sold is established. The Company’s policy is that technological feasibility is achieved when a working model, with the key features and functions of the product, is available for customer testing. Software development costs incurred after the establishment of technological feasibility and until the product is available for general release are capitalized, provided recoverability is reasonably assured. Capitalized software development costs are amortized over their estimate useful life and recorded within cost of revenues - product.
Foreign Currency Translation	Foreign Currency Translation The financial statements of the Company’s foreign subsidiaries are translated in accordance with ASC 830, Foreign Currency Matters. The reporting currency for the Company is the U.S. dollar. The functional currency of the Company’s foreign subsidiaries is determined based on the guidance in ASC 830. The majority of the Company's foreign subsidiaries' functional currency is the applicable local currency, although certain of the Company's foreign subsidiaries' functional currency is the U.S. dollar based on the nature of their operations or functions. Assets and liabilities of subsidiaries whose functional currency is the local currency are translated at the exchange rate in effect at each balance sheet date. Before translation, the Company re-measures foreign currency denominated assets and liabilities, including inter-company accounts receivable and payable, into the functional currency of the respective entity, resulting in unrealized gains or losses recorded in other income (expense), net in the Consolidated Statements of Income. Revenues and expenses are translated using average exchange rates during the respective period. Foreign currency translation adjustments are accumulated as a component of other comprehensive income (loss) as a separate component of stockholders’ equity. Gains and losses arising from transactions denominated in foreign currencies are included in other income (expense), net in the Consolidated Statements of Income and were not significant in any of the reporting periods presented.
Accumulated Other Comprehensive Income	Accumulated Other Comprehensive Income (Loss) Other comprehensive income (loss) includes certain transactions that have generally been reported in the statement of stockholders’ equity.
Derivatives	Derivatives Interest Rate Cap - Cash Flow Hedge The Company is exposed to certain risks arising from both its business operations and economic conditions. The Company manages its exposure to some of its interest rate risk through the use of interest rate caps, which are derivative financial instruments. The Company does not use derivatives for speculative purposes. For a derivative that is designated as a cash flow hedge, changes in the fair value of the derivative are recognized in accumulated other comprehensive income ("AOCI") to the extent the derivative is effective at offsetting the changes in the cash flows being hedged until the hedged item affects earnings. To the extent there is any hedge ineffectiveness, changes in fair value relating to the ineffective portion are immediately recognized in earnings in other income (expense) in the Consolidated Statements of Income. During fiscal 2015, the Company entered into separate interest rate cap agreements with multiple counter-parties to help mitigate the interest rate volatility associated with the variable rate interest on its credit facilities under its Prior Credit Agreement, which was replaced by the Credit Agreement in 2015 (see Note 5). Interest rate cap agreements provide the right to receive cash if the reference interest rate rises above a contractual rate. The aggregate premium paid for the interest rate cap agreements was $13.2 million , which was the initial fair value of the instruments recorded in the Company's financial statements. Certain of these cap agreements expired during fiscal 2017. During fiscal 2017, the Company entered into new separate interest rate cap agreements with multiple counter-parties to extend the expiration date of its hedges by an additional year. The aggregate premium paid for the interest rate cap agreements was $1.9 million , which was the initial fair value of the instruments recorded in the Company's financial statements. The critical terms of the interest rate caps were designed to mirror the terms of the Company’s LIBOR-based borrowings under the Prior Credit Agreement. The terms in the 2015 Credit Agreement are consistent with the Prior Credit Agreement, and therefore the interest rate caps continue to be highly effective at offsetting the cash flows being hedged. The Company designated these derivatives as cash flow hedges of the variability of the LIBOR-based interest payments on $1.0 billion of principal, which ends on December 30, 2018. As of September 30, 2017 , the Company determined that the existence of hedge ineffectiveness, if any, was immaterial and all changes in the fair value of the interest rate caps were recorded in the Consolidated Statements of Comprehensive Income as a component of AOCI. During fiscal 2017 and 2016, interest expense of $6.9 million and $3.9 million , respectively, was reclassified from AOCI to the Company's Consolidated Statements of Income related to the interest rate cap agreements. The Company expects to similarly reclassify approximately $3.6 million from AOCI to the Consolidated Statements of Income in the next twelve months. The aggregate fair value of these interest rate caps was $4.8 million and $1.4 million at September 30, 2017 and September 24, 2016 , respectively, and is included in both Prepaid expenses and other current assets and Other assets on the Company’s Consolidated Balance Sheet. Refer to Note 6 “Fair Value Measurements” below for related fair value disclosures. Forward Foreign Currency Contracts The Company enters into forward foreign currency exchange contracts to mitigate certain operational exposures from the impact of changes in foreign currency exchange rates. Such exposures result from the portion of the Company's operations that are denominated in currencies other than the U.S. dollar, primarily the Euro, the UK Pound, the Australian dollar, the Canadian dollar and the Japanese Yen. These foreign currency exchange contracts are entered into to support transactions made in the ordinary course of business and are not speculative in nature. The contracts are generally for periods of one year or less. During fiscal 2016, the Company began to execute forward foreign currency contracts in order to mitigate its exposure to fluctuations in various currencies against its reporting currency, the U.S. dollar. The Company executed additional contracts in fiscal 2017. The Company did not elect hedge accounting for these forward foreign currency contracts; however, the Company may seek to apply hedge accounting in future scenarios. The change in the fair value of these contracts is recognized directly in earnings as a component of other income (expense), net.
Revenue Recognition	Revenue Recognition The Company generates revenue from the sale of its products, primarily medical imaging systems, aesthetic treatment systems and diagnostic and surgical disposable products, and related services, which are primarily support and maintenance services on its medical imaging systems. The Company recognizes product revenue upon shipment provided that there is persuasive evidence of an arrangement, there are no uncertainties regarding acceptance, the sales price is fixed or determinable, and collection of the resulting receivable is reasonably assured. Generally, the Company’s product arrangements for capital equipment sales, primarily in its Breast Health, Medical Aesthetics and Skeletal Health reporting segments, are multiple-element arrangements, including services, such as installation, training and support and maintenance, and multiple products. Based on the terms and conditions of the product arrangements, the Company believes that these services and undelivered products can be accounted for separately from the delivered product element as the Company’s delivered products have value to its customers on a stand-alone basis. Accordingly, revenue for services not yet performed at the time of product delivery are deferred and recognized as such services are performed. The relative selling price of any undelivered products is also deferred at the time of shipment and recognized as revenue when these products are delivered. There is no customer right of return in the Company’s sales agreements for its capital equipment. Service revenues primarily consist of amounts recorded under service and maintenance contracts and repairs not covered under warranty, installation and training, and shipping and handling costs billed to customers. Service and maintenance contract revenues are recognized ratably over the term of the contract. Other service revenues are recognized as the services are performed. Service and other revenue also includes royalties which are recognized in the period the payments are due to the Company. For revenue arrangements with multiple deliverables, the Company records revenue as separate units of accounting if the delivered items have value to the customer on a stand-alone basis, and if the arrangement includes a general right of return relative to the delivered items, the delivery or performance of the undelivered items is considered probable and substantially within the Company’s control. Some of the Company’s products have both software and non-software components that function together to deliver the product’s essential functionality. The Company determined that except for its computer-aided detection (“CAD”) products and C-View and Intelligent 2D products, the software element in its other products is not within the scope of the software revenue recognition rules, ASC 985-605, Software—Revenue Recognition . The Company determined that given the significance of the software component’s functionality to its CAD, C-View and Intelligent 2D components, which are sold by its Breast Health segment, these products are within the scope of the software revenue recognition rules. The Company evaluated the appropriate revenue recognition treatment of it hardware products, including its Dimensions digital mammography systems, which have both software and non-software components that function together to deliver the products’ essential functionality (i.e., it is a tangible product), and determined they are not within the scope of ASC 985-605. The Company is required to allocate revenue to its multiple element arrangements based on the relative fair value of each element’s selling price. The Company typically determines the selling price of its products based on its best estimate of selling prices (“ESP”) and services based on vendor-specific objective evidence of selling price (“VSOE”). The Company determines VSOE based on its normal pricing and discounting practices for the specific product or service when sold on a stand-alone basis. In determining VSOE, the Company’s policy requires a substantial majority of selling prices for a product or service to be within a reasonably narrow range. The Company also considers the class of customer, method of distribution, and the geographies into which its products and services are sold when determining VSOE. If VSOE cannot be established, which may occur in instances when a product or service has not been sold separately, stand-alone sales are too infrequent, or product pricing is not within a relatively narrow range, the Company will generally establish the selling price using ESP to allocate arrangement consideration. The objective of ESP is to determine the price at which the Company would typically transact a stand-alone sale of the product or service. ESP is determined by considering a number of factors including Company pricing policies, internal costs and gross margin objectives, method of distribution, information gathered from experience in customer negotiations, market research and information, recent technological trends, competitive landscape and geographies. For those arrangements accounted for under the software revenue recognition rules, ASC 985-605 generally requires revenue earned on software arrangements involving multiple elements to be allocated to each element based on their relative VSOE of fair value. If VSOE does not exist for a delivered element, the residual method is applied in which the arrangement consideration is allocated to the undelivered elements based on their VSOE with the remaining consideration recognized as revenue for the delivered elements. For multiple-element software arrangements where VSOE of fair value of Post-Contract Customer Support (“PCS”) has been established, the Company recognizes revenue using the residual method at the time all other revenue recognition criteria have been met. Within its Diagnostics segment, the Company manufactured blood screening products according to demand schedules provided by its former collaboration partner, Grifols, S.A. (“Grifols”). In the second quarter of fiscal 2017, the Company sold its assets in the blood screening business to Grifols. Upon the closing of the transaction, the Company's existing collaboration agreement with Grifols terminated, and a new collaboration agreement was executed as part of this transaction for the Company to provide certain research and development services to Grifols. In addition, the Company agreed to provide transition services to Grifols over the next two to three years depending on the nature of the respective service, including the manufacture of inventory, and the Company is in effect serving as a contract manufacturer of assays to Grifols for a two to three year period. The Company also agreed to sell Panther instrumentation and certain supplies to Grifols as part of a long term supply agreement. As such, the Company will generate a level of revenues, but much lower than historical trends. Prior to divestiture, the Company’s agreement provided that it would share a portion of Grifols’s revenue from screening blood donations. Upon shipment to Grifols, the Company recognized product revenue at an agreed upon fixed transfer price, which was not refundable, and recorded the related cost of products sold. Based on the terms of the Company’s prior collaboration agreement with Grifols, the Company’s ultimate share of the net revenue from sales to the end user in excess of the transfer price was not known until it was reported to the Company by Grifols. On a monthly basis, Grifols reported net revenue generated during the prior month and remitted an additional corresponding net payment to the Company, which was recorded as revenue at that time. This payment combined with the transfer price revenues previously recognized represented the Company’s ultimate share of net revenue under the prior agreement. While the majority of its instruments are placed at customer sites, in certain instances the Company sells instruments to its clinical diagnostics customers and records sales of these instruments upon shipment or delivery, depending on the terms of the arrangement. Within its Diagnostics business, and to a lesser extent, its GYN Surgical business, the Company provides its instrumentation (for example, the ThinPrep Processor, ThinPrep Imaging System, and the Panther and Tigris systems) and certain other hardware to customers without requiring them to purchase the equipment or enter into a lease. The Company installs the instrumentation or equipment at the customer’s site and recovers the cost of providing the instrumentation or equipment in the amount it charges for its diagnostic tests, assays and other disposables. Customers enter into a customer usage agreement and typically commit to purchasing minimum quantities of disposable products at a stated price over a defined contract term, which is typically between three and five years. Revenue is recognized over the term of the customer usage agreement as tests, assays and other disposable products are shipped or delivered, depending on the customer's arrangement.
Accounts Receivable and Reserves	Accounts Receivable and Reserves The Company records reserves for doubtful accounts based upon a specific review of all outstanding invoices, known collection issues and historical experience. The Company regularly evaluates the collectability of its trade accounts receivables and performs ongoing credit evaluations of its customers and adjusts credit limits based upon payment history and its assessment of the customer’s current credit worthiness.
Cost of Service and Other Revenues	Cost of Service and Other Revenues Cost of service and other revenues primarily represents payroll and related costs associated with the Company’s professional services’ employees, consultants, infrastructure costs and overhead allocations, including depreciation, rent and materials consumed in providing the service.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for share-based payments in accordance with ASC 718, Stock Compensation (ASC 718) . As such, all share-based payments to employees, including grants of stock options, restricted stock units, performance stock units and market stock units and shares issued under the Company’s employee stock purchase plan, are recognized in the Consolidated Statements of Income based on their fair values on the date of grant. In March 2016, the FASB issued Accounting Standards Update No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share Based Payment Accounting (ASU 2016-09). This guidance changes how companies account for certain aspects of share-based payments to employees. The amendments in the update are effective for annual periods beginning after December 15, 2016, and were applicable to the Company in fiscal 2018 with early adoption permitted in any interim or annual period. During the first quarter of fiscal 2017, the Company elected to early adopt this standard. The update requires certain changes to presentation of the financial statements as follows: • All excess tax benefits and deficiencies are recognized as a component of the provision for income taxes on a discrete basis in the period in which the equity awards vest and/or are settled. Previously, the Company recorded this tax impact directly to additional paid in capital. For fiscal 2017, the Company recorded a tax benefit of $10.3 million . The standard does not permit retroactive presentation of this benefit to prior fiscal years on the Consolidated Statements of Income. • The tax benefit or deficiency is required to be classified as a cash flow provided by (used in) operating activities. It was previously required to be presented as a cash flow provided by financing activities in the Consolidated Statements of Cash Flows, with a corresponding adjustment to operating cash flows. As permitted by ASU 2016-09, the Company has elected to adopt this classification on a retrospective basis, and therefore, the Consolidated Statement of Cash Flows for fiscal 2016 and 2015 have been recast for this provision resulting in an increase cash flows provided by operations of $11.0 million and $10.7 million , respectively, with a corresponding increase to cash flows used in financing activities. • In the diluted net earnings per share calculation, when applying the treasury stock method for shares that could be repurchased, the assumed proceeds no longer include the amount of excess tax benefit. This provision, which is only applicable on a prospective basis, did not have a material impact on the Company's diluted net earnings per share calculation in fiscal 2017. • ASU 2016-09 allows a Company to elect to account for award forfeitures as they occur or to continue to estimate forfeitures. The Company has elected to continue to estimate potential forfeitures. As such, there is no impact from a change in accounting principle within stockholders' equity.
Net Income Per Share	Net Income Per Share Basic net income per share is computed by dividing net income by the weighted average number of common shares outstanding. Diluted net income per share is computed by dividing net income by the weighted average number of common shares and the dilutive effect of potential future issuances of common stock from outstanding stock options, restricted stock units and convertible debt determined by applying the treasury stock method. In accordance with ASC 718, the assumed proceeds under the treasury stock method include the average unrecognized compensation expense of in-the-money stock options and restricted stock units. This results in the assumed buyback of additional shares, thereby reducing the dilutive impact of equity awards. The Company applies the provisions of ASC 260, Earnings Per Share, Subsection 10-45-44, to determine the diluted weighted average shares outstanding as it relates to its convertible notes, and due to the type of debt instrument issued and its accounting policy, the Company applies the treasury stock method and not the if-converted method. The dilutive impact of the Company’s convertible notes is based on the difference between the Company’s current period average stock price and the conversion price of the convertible notes, provided there is a premium. As such, dilution related to the conversion premium on the 2010 Notes, 2012 Notes and 2013 Notes is included in the calculation of diluted weighted-average shares outstanding in all years to the extent each issuance is dilutive based on the average stock price during each reporting period being greater than the conversion price of the respective Notes.
Product Warranties	Product Warranties The Company generally offers a one -year warranty for its products. The Company provides for the estimated cost of product warranties at the time product revenue is recognized. Factors that affect the Company’s warranty reserves include the number of units sold, historical and anticipated rates of warranty repairs and the cost per repair. The Company periodically assesses the adequacy of the warranty reserve and adjusts the amount as necessary.
Advertising Costs	Advertising Costs Advertising costs are charged to operations as incurred. The Company does not have any direct-response advertising. Advertising costs, which include trade shows and conventions, were approximately $22.5 million , $20.2 million and $14.4 million for fiscal 2017 , 2016 and 2015 , respectively, and were included in selling and marketing expense in the Consolidated Statements of Income.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350) . This guidance simplifies how companies calculate goodwill impairments by eliminating Step 2 of the impairment test. The guidance requires companies to compare the fair value of a reporting unit to its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value. The guidance is effective for annual periods beginning after December 15, 2019, and is applicable to the Company in fiscal 2020. Early adoption is permitted. In October 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740). The guidance requires companies to recognize the income tax effects of intercompany sales and transfers of assets, other than inventory, in the income statement as income tax expense (or benefit) in the period in which the transfer occurs. The guidance is effective for annual periods beginning after December 15, 2017, and is applicable to the Company in fiscal 2019. Early adoption is permitted as of the beginning of an annual reporting period. The Company is currently evaluating the impact of the adoption of ASU 2016-16 on its consolidated financial position and results of operations. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flow (Topic 230) . The guidance reduces diversity in how certain cash receipts and cash payments are presented and classified in the Statements of Cash Flows. Certain of ASU 2016-15 requirements are as follows: 1) cash payments for debt prepayment or debt extinguishment costs should be classified as cash outflows for financing activities, 2) contingent consideration payments made soon after a business combination should be classified as cash outflows for investing activities and cash payment made thereafter should be classified as cash outflows for financing up to the amount of the contingent consideration liability recognized at the acquisition date with any excess classified as operating activities, 3) cash proceeds from the settlement of insurance claims should be classified on the basis of the nature of the loss, 4) cash proceeds from the settlement of Corporate-Owned Life Insurance (COLI) Policies should be classified as cash inflows from investing activities and cash payments for premiums on COLI policies may be classified as cash outflows for investing activities, operating activities, or a combination of investing and operating activities, and 5) cash paid to a tax authority by an employer when withholding shares from an employee's award for tax-withholding purposes should be classified as cash outflows for financing activities. The guidance is effective for annual periods beginning after December 15, 2017, and is applicable to the Company in fiscal 2019. Early adoption is permitted. The adoption of ASU 2016-15 is not expected to have a material effect on the Company's consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326) . The guidance requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis. The income statement reflects the measurement of credit losses for newly recognized financial assets, as well as the expected credit losses during the period. The measurement of expected credit losses is based upon historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. Credit losses relating to available-for-sale debt securities will be recorded through an allowance for credit losses rather than as a direct write-down to the security. The updated guidance is effective for annual periods beginning after December 15, 2019, and is applicable to the Company in fiscal 2021. Early adoption is permitted. The Company is currently evaluating the impact of the adoption of ASU 2016-13 on its consolidated financial position and results of operations. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The guidance requires an entity to recognize a right-of-use asset and a lease liability for virtually all of its leases with terms of more than 12 months. Recognition, measurement and presentation of expenses will depend on classification as a finance or operating lease. The amendments also require certain quantitative and qualitative disclosures about leasing arrangements. The guidance is effective for annual periods beginning after December 15, 2018, and is applicable to the Company in fiscal 2020. Early adoption is permitted. The updated guidance requires a modified retrospective adoption. The Company is currently evaluating the anticipated impact of the adoption of ASU 2016-02 on its consolidated financial position and results of operations. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities . This guidance changes how entities measure equity investments that do not result in consolidation and are not accounted for under the equity method. Entities will be required to measure these investments at fair value at the end of each reporting period and recognize changes in fair value in net income. A practicability exception will be available for equity investments that do not have readily determinable fair values, however; the exception requires the Company to consider relevant transactions that can be reasonably known to identify any observable price changes that would impact the fair value . This guidance also changes certain disclosure requirements and other aspects of current U.S. GAAP. This guidance is effective for annual periods beginning after December 15, 2017, and is applicable to the Company in fiscal 2019 . Early adoption is permitted. The Company is currently evaluating the anticipated impact of the adoption of ASU 2016-01 on its consolidated financial position and results of operations. In July 2015, the FASB issued guidance under ASC 330, Simplifying the Measurement of Inventory. The new guidance requires inventory to be measured at the lower of cost and net realizable value, which is defined as the estimated selling price in the ordinary course of business less reasonably predictable costs of completion, disposal and transportation. This new guidance is effective for the Company's first quarter of fiscal 2018 and early adoption is permitted. The guidance must be applied prospectively. The Company is currently evaluating the impact of the adoption of this requirement on its consolidated financial statements but does not anticipate that adoption of this guidance will have a material impact on its consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) , which provides guidance for revenue recognition. This ASU is applicable to any entity that either enters into contracts with customers to transfer goods or services or enters into contracts for the transfer of nonfinancial assets. ASU 2014-09 will supersede the revenue recognition requirements in Topic 605, Revenue Recognition , and most industry-specific guidance. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled to receive in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under current U.S. GAAP. These judgments may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. On July 9, 2015, the FASB voted in favor of delaying the effective date of the new standard by one year, with early adoption permitted as of the original effective date. ASU 2014-09 is effective prospectively for fiscal years, and interim reporting periods within those years, beginning after December 15, 2017, which is fiscal 2019 for the Company. The Company will adopt Topic 606 effective September 30, 2018 and has established a cross-functional team to evaluate and implement the new revenue recognition rules. The Company will adopt Topic 606 using the modified retrospective method but has not finalized evaluating the anticipated impact of the adoption of ASU 2014-09 on its consolidated financial position and results of operations.
Recently Issued Accounting Pronouncements

Summary of Significant Accoun27

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Marketable Securities	The following reconciles cost basis to fair market value. Cost Gross Unrealized Gross Unrealized Other Than Temporary Impairment Fair Value As of September 30, 2017 $ 0.7 $ — $ (0.6 ) $ — $ 0.1 As of September 24, 2016 $ 2.4 $ — $ (0.3 ) $ (1.1 ) $ 1.0 As of September 26, 2015 $ 16.1 $ 7.2 $ (0.3 ) $ (7.8 ) $ 15.2
Supplemental Cash Flow Statement Information	Supplemental Cash Flow Statement Information Years ended September 30, 2017 September 24, 2016 September 26, 2015 Cash paid during the period for income taxes $ 867.8 $ 184.8 $ 168.7 Cash paid during the period for interest $ 102.4 $ 104.0 $ 143.0
Schedule of Inventories	Inventories consisted of the following: September 30, 2017 September 24, 2016 Raw materials $ 95.7 $ 96.4 Work-in-process 45.0 51.7 Finished goods 190.9 126.6 $ 331.6 $ 274.7
Schedule of Property, Plant and Equipment	Property, plant and equipment consisted of the following: September 30, 2017 September 24, 2016 Equipment and software $ 422.4 $ 381.9 Equipment under customer usage agreements 368.7 334.6 Buildings and improvements 172.0 186.1 Leasehold improvements 60.6 65.6 Land 46.3 51.9 Furniture and fixtures 20.8 18.4 1,090.8 1,038.5 Less - accumulated depreciation and amortization (599.6 ) (578.3 ) $ 491.2 $ 460.2 Property, plant and equipment are depreciated over the following estimated useful lives: Asset Classification Estimated Useful Life Building and improvements 20–35 years Equipment and software 3–10 years Equipment under customer usage agreements 3–8 years Furniture and fixtures 5–7 years Leasehold improvements Shorter of the Original Term of Lease or Estimated Useful Life
Schedule of Intangible Assets	Intangible assets consisted of the following: September 30, 2017 September 24, 2016 Description Gross Carrying Value Accumulated Amortization Gross Carrying Value Accumulated Amortization Developed technology $ 4,528.7 $ 2,186.8 $ 3,983.7 $ 1,991.6 In-process research and development 46.0 — 3.7 — Customer relationships 552.8 393.8 1,098.9 546.2 Trade names 310.3 156.4 236.2 141.6 Distribution agreement 42.0 2.8 — — Non-competition agreements 1.5 0.1 — — Business licenses 2.4 2.2 2.4 2.1 $ 5,483.7 $ 2,742.1 $ 5,324.9 $ 2,681.5
Schedule of Estimated Amortization Expense	The estimated amortization expense at September 30, 2017 for each of the five succeeding fiscal years was as follows: Fiscal 2018 $ 376.6 Fiscal 2019 $ 364.9 Fiscal 2020 $ 353.6 Fiscal 2021 $ 332.2 Fiscal 2022 $ 319.8
Rollforward of Goodwill Activity by Reportable Segment	A rollforward of goodwill activity by reportable segment from September 24, 2016 to September 30, 2017 is as follows: Diagnostics Breast Health Medical Aesthetics GYN Surgical Skeletal Health Total Balance at September 24, 2016 $ 1,148.2 $ 631.8 $ — $ 1,015.0 $ 8.1 $ 2,803.1 Acquisitions — 8.9 683.5 — — 692.4 Sale of blood screening business (325.0 ) — — — — (325.0 ) Foreign currency and other adjustments (0.2 ) 0.8 — 0.1 — 0.7 Balance at September 30, 2017 $ 823.0 $ 641.5 $ 683.5 $ 1,015.1 $ 8.1 $ 3,171.2
Schedule of Other Assets	Other assets consisted of the following: September 30, 2017 September 24, 2016 Other Assets Life insurance contracts $ 41.0 $ 36.0 Capitalized software 12.3 10.0 Manufacturing access fees 7.1 9.6 Cost-method equity investments 3.0 3.5 Deferred tax assets 9.1 9.3 Other 24.5 15.3 $ 97.0 $ 83.7
Changes in accumulated balances of other comprehensive income	The following tables summarize the components and changes in accumulated balances of other comprehensive income for the periods presented: Year Ended September 30, 2017 Year Ended September 24, 2016 Foreign Currency Translation Marketable Securities Pension Plans Hedged Interest Rate Caps Total Foreign Currency Translation Marketable Securities Pension Plans Hedged Interest Rate Caps Total Beginning Balance $ (26.1 ) $ (0.3 ) $ (2.5 ) $ (3.4 ) $ (32.3 ) $ (15.7 ) $ 6.9 $ (1.8 ) $ (3.9 ) $ (14.5 ) Other comprehensive loss before reclassifications 7.6 2.3 0.9 0.8 11.6 (10.4 ) (1.1 ) (0.7 ) (3.4 ) (15.6 ) (Gains) charges reclassified to statement of income — (2.4 ) — 6.9 4.5 — (6.1 ) — 3.9 (2.2 ) Ending Balance $ (18.5 ) $ (0.4 ) $ (1.6 ) $ 4.3 $ (16.2 ) $ (26.1 ) $ (0.3 ) $ (2.5 ) $ (3.4 ) $ (32.3 )
Schedule of Derivative Instruments on the Consolidated Balance Sheets	The table below presents the fair value of the Company's derivative financial instruments as well as their classification on the balance sheet as of September 30, 2017 : Balance Sheet Location September 30, 2017 September 24, 2016 Assets: Derivative instruments designated as a cash flow hedge: Interest rate cap agreements Prepaid expenses and other current assets $ 3.6 $ 1.0 Interest rate cap agreements Other Assets 1.2 0.4 $ 4.8 $ 1.4 Derivatives not designated as hedging instruments: Forward foreign currency contracts Prepaid expenses and other current assets $ 0.4 $ 0.2 Liabilities: Derivatives not designated as hedging instruments: Forward foreign currency contracts Accrued expenses $ 4.0 $ 1.3
Schedule of Unrealized Loss Recognized in AOCI	The following table presents the unrealized loss recognized in AOCI related to the interest rate caps for the following reporting periods: Year Ended Year Ended Year Ended Amount of loss recognized in other comprehensive income, net of taxes: Interest rate cap agreements $ 0.8 $ (3.4 ) $ (3.9 )
Gain (Loss) on Fair Value Hedges Recognized in Earnings	The following table presents the adjustment to fair value (realized and unrealized) recorded within the Consolidated Statements of Income for derivative instruments for which the Company did not elect hedge accounting: Derivatives not classified as hedging instruments Location of Gain (Loss) Recognized in Income Year Ended Year Ended Forward foreign currency contracts $ 0.5 $ 0.4 Other income (expense), net
Accounts Receivable Reserve Activity	Accounts receivable reserve activity for fiscal 2017 , 2016 and 2015 was as follows: Balance at Beginning of Period Charged to Costs and Expenses Write- offs and Payments Balance at End of Period Period Ended: September 30, 2017 $ 12.7 $ 1.8 $ (4.7 ) $ 9.8 September 24, 2016 $ 11.1 $ 2.0 $ (0.4 ) $ 12.7 September 26, 2015 $ 12.0 $ 1.6 $ (2.5 ) $ 11.1
Schedule of Reconciliation of Basic and Diluted Share Amounts	A reconciliation of basic and diluted share amounts for fiscal 2017 , 2016 , and 2015 was as follows: September 30, 2017 September 24, 2016 September 26, 2015 Basic weighted average common shares outstanding 279,811 280,213 280,566 Weighted average common stock equivalents from assumed exercise of stock options and restricted stock units 2,885 2,631 2,898 Incremental shares from convertible notes premium 2,957 3,312 6,073 Diluted weighted average common shares outstanding 285,653 286,156 289,537 Weighted-average anti-dilutive shares related to: Outstanding stock options 1,677 1,029 1,502 Restricted stock units 12 62 49
Schedule of Product Warranty Activity	Product warranty activity for fiscal 2017 and 2016 was as follows: Balance at Beginning of Period Acquired Provisions Settlements/ Adjustments Balance at End of Period Period ended: September 30, 2017 $ 5.0 $ 9.9 $ 15.3 $ (13.2 ) $ 17.0 September 24, 2016 $ 5.4 $ — $ 7.1 $ (7.5 ) $ 5.0

Summary of Significant Accoun28

Summary of Significant Accounting Policies - Gain (Loss) on Fair Value Hedges Recognized in Earnings (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016
Forward foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	$ 0.5	$ 0.4

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Schedule of Purchase Price	The preliminary purchase price allocation is as follows: Cash $ 107.2 Marketable securities 82.9 Accounts receivable 40.2 Inventory 121.1 Property, plant and equipment 44.1 Other assets and liabilities, net 12.2 Accounts payable and accrued expenses (75.3 ) Deferred revenue (11.2 ) Capital lease obligation (25.2 ) Identifiable intangible assets: Developed technology 736.0 In-process research and development 107.0 Distribution agreement 42.0 Customer relationships 35.0 Trade names 74.0 Deferred income taxes, net (315.7 ) Goodwill 683.5 Purchase Price $ 1,657.8
Schedule of Pro Forma Information	The following unaudited pro forma information presents the combined financial results for the Company and Cynosure as if the acquisition of Cynosure had been completed at the beginning of the prior fiscal year, September 26, 2015: Twelve Months Ended Twelve Months Ended September 30, 2017 September 24, 2016 (unaudited) (unaudited) Revenue $ 3,241.4 $ 3,244.6 Net income $ 768.5 $ 252.3 Basic earnings per common share $ 2.75 $ 0.90 Diluted earnings per common share $ 2.69 $ 0.88

Restructuring and Divestiture30

Restructuring and Divestiture Charges (Tables)	12 Months Ended
	Sep. 30, 2017
Restructuring and Related Activities [Abstract]
Charges Taken Related to Restructuring Actions	The following table displays charges taken related to restructuring actions in fiscal 2017 , 2016 and 2015 and a rollforward of the charges to the accrued balances as of September 30, 2017 : Fiscal 2017 Actions Fiscal 2016 Actions Fiscal 2015 Actions Fiscal 2014 Actions Other Charges Total Restructuring and Divestiture Charges Fiscal 2015 charges: Workforce reductions $ — $ — $ 10.0 $ 6.0 $ 0.3 $ 16.3 Facility closure costs — — — 2.0 0.6 2.6 Fiscal 2015 restructuring charges $ — $ — $ 10.0 $ 8.0 $ 0.9 $ 18.9 Divestiture net charges 9.6 Fiscal 2015 restructuring and divestiture charges $ 28.5 Fiscal 2016 charges: Workforce reductions $ — $ 10.5 $ — $ — $ — $ 10.5 Fiscal 2016 restructuring charges $ — $ 10.5 $ — $ — $ — $ 10.5 Fiscal 2017 charges: Workforce reductions $ 8.5 $ — $ — $ — $ — $ 8.5 Facility closure costs — 4.8 — — — 4.8 Other — — — — — — Fiscal 2017 restructuring charges $ 8.5 $ 4.8 $ — $ — $ — $13.3
Charges Taken Related to Accrued Restructuring Actions	Fiscal 2017 Actions Fiscal 2016 Actions Fiscal 2015 Actions Fiscal 2014 Actions Other Charges Total Rollforward of Accrued Restructuring Balance as of September 27, 2014 $ — $ — $ — $ 12.0 $ 4.9 $ 16.9 Fiscal 2015 restructuring charges $ — $ — $ 10.0 $ 8.0 $ 0.9 $ 18.9 Stock-based compensation — — (4.1 ) — — (4.1 ) Severance payments — — (2.8 ) (16.2 ) (4.9 ) (23.9 ) Other payments — — — (1.3 ) (0.8 ) (2.1 ) Balance as of September 26, 2015 $ — $ — $ 3.1 $ 2.5 $ 0.1 $ 5.7 Fiscal 2016 restructuring charges $ — $ 10.5 $ — $ — $ — $ 10.5 Stock-based compensation — (0.4 ) — — — (0.4 ) Severance payments — (4.6 ) (2.9 ) (1.4 ) (0.1 ) (9.0 ) Other payments — — — (0.5 ) — (0.5 ) Balance as of September 24, 2016 $ — $ 5.5 $ 0.2 $ 0.6 $ — $ 6.3 Fiscal 2017 restructuring charges $ 8.5 $ 4.8 $ — $ — $ — $ 13.3 Severance payments (1.0 ) (5.4 ) (0.2 ) — — (6.6 ) Other payments — (1.2 ) — (0.3 ) — (1.5 ) Balance as of September 30, 2017 $ 7.5 $ 3.7 $ — $ 0.3 $ — $ 11.5

Borrowings and Credit Arrange31

Borrowings and Credit Arrangements (Tables)	12 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Company's Borrowings	The Company’s borrowings consisted of the following: September 30, September 24, Current debt obligations, net of debt discount and issuance costs: Term Loan $ 121.3 $ 83.8 Revolver 345.0 — Securitization Program 200.0 200.0 Convertible Notes 484.5 12.2 Total current debt obligations 1,150.8 296.0 Long-term debt obligations, net of debt discount and issuance costs: Term Loan 1,190.5 1,308.2 2022 Senior Notes 981.6 977.7 Convertible Notes — 763.5 Total long-term debt obligations 2,172.1 3,049.4 Total debt obligations $ 3,322.9 $ 3,345.4
Schedule Of Long Term Debt By Maturity Table	The debt maturity schedule for the Company’s obligations as of September 30, 2017 is as follows: 2018 2019 2020 2021 2022 2023 and Thereafter Total Term Loan $ 121.9 $ 150.0 $ 1,050.0 $ — $ — $ — $ 1,321.9 Revolver 345.0 — — — — — 345.0 Securitization Program 200.0 — — — — — 200.0 2022 Senior Notes — — — — 1,000.0 — 1,000.0 Convertible Notes (1) 488.3 — — — — 488.3 $ 1,155.2 $ 150.0 $ 1,050.0 $ — $ 1,000.0 $ — $ 3,355.2 (1) Classified based on the earliest date of redemption for each respective issuance. In addition, the balance in fiscal 2018 reflects accretion on the 2013 Notes through September 30, 2017.
Schedule Of Convertible Notes And Related Equity Components Recorded In Capital In Excess Of Par Value Net Of Deferred Taxes Table	As of September 30, 2017 and September 24, 2016 , the Convertible Notes and related equity components (recorded in additional paid-in-capital, net of deferred taxes) consisted of the following: 2017 2016 2010 Notes principal amount $ — $ 12.3 Unamortized discount and issuance costs — (0.1 ) Net carrying amount $ — $ 12.2 Equity component, net of taxes $ — $ 1.6 2012 Notes principal amount $ 245.4 $ 363.4 Unamortized discount and issuance costs (1.9 ) (9.5 ) Net carrying amount $ 243.5 $ 353.9 Equity component, net of taxes $ 24.1 $ 35.8 2013 Notes principal amount $ 202.0 $ 370.0 Principal accretion 40.8 57.1 Unamortized discount and issuance costs (1.8 ) (17.5 ) Net carrying amount $ 241.0 $ 409.6 Equity component, net of taxes $ 71.8 $ 131.5
Interest Expense under Convertible Notes	Interest expense under the Convertible Notes is as follows: Years Ended September 30, September 24, September 26, Amortization of debt discount $ 17.9 $ 22.3 $ 34.9 Amortization of deferred financing costs 0.8 1.1 1.7 Principal accretion 15.6 16.6 15.9 Non-cash interest expense 34.3 40.0 52.5 2.00% accrued interest (cash) 6.7 10.0 18.2 $ 41.0 $ 50.0 $ 70.7

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Assets and Liabilities Measured on Recurring Basis	Assets and liabilities measured and recorded at fair value on a recurring basis consisted of the following: Fair Value Measurements at September 30, 2017 Carrying Value Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Equity securities $ 0.1 $ 0.1 $ — $ — Interest rate caps - derivative 4.8 — 4.8 — Forward foreign currency contracts 0.4 — 0.4 — Total $ 5.3 $ 0.1 $ 5.2 $ — Liabilities: Deferred compensation liabilities $ 43.2 $ 43.2 $ — $ — Forward foreign currency contracts 4.0 — 4.0 — Total $ 47.2 $ 43.2 $ 4.0 $ — Fair Value Measurements at September 24, 2016 Carrying Value Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Equity securities $ 1.0 $ 1.0 $ — $ — Interest rate caps - derivative 1.4 — 1.4 — Forward foreign currency contracts 0.2 — 0.2 — Total $ 2.6 $ 1.0 $ 1.6 $ — Liabilities: Deferred compensation liabilities $ 37.0 $ 37.0 $ — $ — Forward foreign currency contracts 1.3 — 1.3 — Total $ 38.3 $ 37.0 $ 1.3 $ —
Estimated Fair Values of Convertible Notes	The estimated fair values of the Company’s Convertible Notes at September 30, 2017 and September 24, 2016 are as follows: 2017 2016 2010 Notes — 20.2 2012 Notes 297.3 481.9 2013 Notes 244.4 458.8 $ 541.7 $ 960.9

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income (Loss) Before Income Taxes	The Company’s income before income taxes consisted of the following: Years ended September 30, 2017 September 24, 2016 September 26, 2015 Domestic $ 1,105.8 $ 310.7 $ 158.3 Foreign 124.7 104.6 18.9 $ 1,230.5 $ 415.3 $ 177.2
Provision for Income Taxes	The provision for income taxes contained the following components: Years ended September 30, 2017 September 24, 2016 September 26, 2015 Federal: Current $ 701.1 $ 209.0 $ 185.2 Deferred (276.9 ) (122.7 ) (137.0 ) 424.2 86.3 48.2 State: Current 53.1 16.6 3.5 Deferred (15.9 ) (22.7 ) (11.0 ) 37.2 (6.1 ) (7.5 ) Foreign: Current 13.9 14.7 5.7 Deferred (0.3 ) (10.4 ) (0.8 ) 13.6 4.3 4.9 $ 475.0 $ 84.5 $ 45.6
Reconciliation of Income Tax (Benefit) at U.S. Federal Statutory Rate to Company's Effective Tax Rate	The income tax provision differed from the tax provision computed at the U.S. federal statutory rate due to the following: Years ended September 30, 2017 September 24, 2016 September 26, 2015 Income tax provision at federal statutory rate 35.0 % 35.0 % 35.0 % Increase (decrease) in tax resulting from: Domestic production activities deduction (1.7 ) (5.0 ) (10.1 ) State income taxes, net of federal benefit 2.3 2.0 1.2 Non-deductible goodwill 9.2 — — Tax credits (0.8 ) (3.2 ) (3.8 ) Unrecognized tax benefits (1.4 ) 2.4 (1.8 ) Cumulative translation adjustment write-off — — 1.9 Compensation (0.5 ) 0.1 1.9 Foreign rate differential (2.6 ) (6.1 ) (1.6 ) Change in deferred tax rate 0.2 (1.8 ) — Change in valuation allowance (1.5 ) (3.4 ) 1.0 Other 0.4 0.3 2.1 38.6 % 20.3 % 25.8 %
Significant Components of the Company's Deferred Tax Assets and Liabilities	The Company’s significant deferred tax assets and liabilities were as follows: September 30, 2017 September 24, 2016 Deferred tax assets Net operating loss carryforwards $ 50.1 $ 40.0 Capital losses 7.1 19.1 Non-deductible accruals 50.6 21.1 Non-deductible reserves 30.0 31.1 Stock-based compensation 39.3 34.8 Research and other credits 13.6 10.7 Nonqualified deferred compensation plan 16.4 14.1 Other temporary differences 16.5 9.2 223.6 180.1 Less: valuation allowance (28.2 ) (46.2 ) $ 195.4 $ 133.9 Deferred tax liabilities Depreciation and amortization $ (1,071.5 ) $ (1,030.8 ) Debt discounts and deferrals (88.4 ) (76.4 ) $ (1,159.9 ) $ (1,107.2 ) $ (964.5 ) $ (973.3 )
Activity of the Company's Unrecognized Income Tax Benefits	The Company’s unrecognized income tax benefits activity for fiscal 2017 and 2016 was as follows: 2017 2016 Balance at beginning of fiscal year $ 163.6 $ 154.7 Tax positions related to current year: Additions 21.8 23.9 Reductions — — Tax positions related to prior years: Additions related to change in estimate 1.1 1.1 Reductions (77.3 ) (6.9 ) Payments (1.6 ) (6.0 ) Lapses in statutes of limitations (19.9 ) (3.2 ) Acquired tax positions: Additions related to reserves acquired from acquisitions 2.6 — Balance as of the end of the fiscal year $ 90.3 $ 163.6

Stockholders' Equity and Stoc34

Stockholders' Equity and Stock-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation Expense in Consolidated Statement of Operations	The following presents stock-based compensation expense in the Company’s Consolidated Statements of Operations in fiscal 2017 , 2016 and 2015 : 2017 2016 2015 Cost of revenues $ 10.7 $ 10.5 $ 8.7 Research and development 11.2 10.8 8.6 Selling and marketing 11.9 10.9 8.8 General and administrative 34.4 32.8 29.1 Restructuring and divestiture — 0.4 4.1 $ 68.2 $ 65.4 $ 59.3
Information Pertaining to Stock Options Granted and Related Assumptions	Information pertaining to stock options granted during fiscal 2017 , 2016 and 2015 and related assumptions are noted in the following table: Years ended September 30, 2017 September 24, 2016 September 26, 2015 Options granted (in millions) 1.0 1.1 1.3 Weighted-average exercise price $ 38.07 $ 39.32 $ 27.68 Weighted-average grant date fair value $ 12.33 $ 12.91 $ 9.95 Assumptions: Risk-free interest rates 1.8 % 1.6 % 1.7 % Expected life (in years) 4.7 4.7 5.3 Expected volatility 36.6 % 37.8 % 38.6 % Dividend yield — — —
Stock Option Activity	The following table summarizes all stock option activity under the Company’s stock option plans for the year ended September 30, 2017 : Number of Shares (in millions) Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (in Years) Aggregate Intrinsic Value (in millions) Options outstanding at September 24, 2016 6.1 $ 25.37 4.9 $ 80.1 Granted 1.0 38.07 Canceled/ forfeited (0.2 ) 30.59 Exercised (1.4 ) 23.25 $ 25.9 Options outstanding at September 30, 2017 5.5 $ 28.15 5.4 $ 50.3 Options exercisable at September 30, 2017 2.6 $ 23.31 3.6 $ 34.8 Options vested and expected to vest at September 30, 2017 (1) 5.4 $ 28.09 5.5 $ 50.0 (1) This represents the number of vested stock options as of September 30, 2017 plus the unvested outstanding options at September 30, 2017 expected to vest in the future, adjusted for estimated forfeitures.
Restricted Stock Unit Activity	A summary of the Company’s RSU activity during the year ended September 30, 2017 is presented below: Non-vested Shares Number of Shares (in millions) Weighted-Average Grant-Date Fair Value Non-vested at September 24, 2016 2.8 $ 29.40 Granted 1.0 38.03 Vested (1.2 ) 27.43 Forfeited (0.3 ) 32.21 Non-vested at September 30, 2017 2.3 $ 34.06
Black-Scholes Model Weighted Average Assumptions Used to Estimate Fair Value of Shares to Be Issued as of Grant Date	The Company uses the Black-Scholes model to estimate the fair value of shares to be issued as of the grant date using the following weighted average assumptions: September 30, 2017 September 24, 2016 September 26, 2015 Assumptions: Risk-free interest rates 0.72 % 0.34 % 0.10 % Expected life (in years) 0.5 0.5 0.5 Expected volatility 24.9 % 27.2 % 27.4 % Dividend yield — — —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments for Capital Leases	Future minimum lease payments, including principal and interest, under these leases were as follows at September 30, 2017 : Fiscal 2018 $ 2.9 Fiscal 2019 1.2 Fiscal 2020 1.2 Fiscal 2021 1.2 Fiscal 2022 1.2 Thereafter 1.7 Total minimum payments 9.4 Less-amount representing interest (3.0 ) Total $ 6.4
Unrecorded Unconditional Purchase Obligations Disclosure	At September 30, 2017 , purchase commitments are as follows: Fiscal 2018 $ 56.4 Fiscal 2019 4.7 Fiscal 2020 1.1 Fiscal 2021 1.1 Fiscal 2022 1.1 Total $ 64.4
Schedule of Future Minimum Rental Payments for Operating Leases	Future minimum lease payments under all of the Company’s operating leases at September 30, 2017 are as follows: Fiscal 2018 $ 20.9 Fiscal 2019 18.0 Fiscal 2020 15.2 Fiscal 2021 12.5 Fiscal 2022 11.4 Thereafter 27.0 Total $ 105.0
Schedule Of Future Minimum Annual Rental Income Payments Under Sublease Agreements	The future minimum annual rental income payments under these sublease agreements at September 30, 2017 are as follows: Fiscal 2018 $ 2.3 Fiscal 2019 2.3 Fiscal 2020 1.5 Fiscal 2021 0.4 Fiscal 2022 0.4 Thereafter 0.7 Total $ 7.6

Disposition (Tables)

Disposition (Tables)	12 Months Ended
	Sep. 30, 2017
Disposal Groups, Including Discontinued Operations and Collaborative Agreement [Abstract]
Schedule of Disposed Business, Income from Operations	Income from operations of the disposed business for the years periods ended September 30, 2017 and September 24, 2016 was as follows: Twelve Months Ended September 30, 2017 September 24, 2016 Income from operations $ 45.8 $ 99.1

Business Segments and Geograp37

Business Segments and Geographic Information (Tables)	12 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Segment Information	Segment information for fiscal 2017 , 2016 , and 2015 was as follows: Years ended September 30, September 24, September 26, Total revenues: Diagnostics $ 1,197.1 $ 1,236.9 $ 1,211.8 Breast Health 1,138.3 1,112.8 1,063.4 Medical Aesthetics 207.5 — — GYN Surgical 427.1 393.1 335.8 Skeletal Health 88.8 89.9 94.0 $ 3,058.8 $ 2,832.7 $ 2,705.0 Operating income: Diagnostics $ 1,054.2 $ 126.0 $ 109.5 Breast Health 373.4 350.5 296.3 Medical Aesthetics (115.9 ) — — GYN Surgical 65.0 69.1 38.6 Skeletal Health (6.5 ) 3.0 10.7 $ 1,370.2 $ 548.6 $ 455.1 Depreciation and amortization: Diagnostics $ 278.9 $ 341.8 $ 358.7 Breast Health 19.7 22.6 28.6 Medical Aesthetics 54.2 — — GYN Surgical 95.7 99.9 102.7 Skeletal Health 0.7 1.1 1.4 $ 449.2 $ 465.4 $ 491.4 Capital expenditures: Diagnostics $ 50.9 $ 53.5 $ 55.6 Breast Health 12.0 10.6 12.8 Medical Aesthetics 7.3 — — GYN Surgical 15.2 17.7 9.5 Skeletal Health 1.2 0.4 0.4 Corporate 21.0 12.3 11.1 $ 107.6 $ 94.5 $ 89.4 September 30, September 24, September 26, Identifiable assets: Diagnostics $ 2,621.6 $ 3,771.9 $ 4,055.8 Breast Health 824.0 809.1 815.4 Medical Aesthetics 1,751.2 — — GYN Surgical 1,494.6 1,570.7 1,658.1 Skeletal Health 25.5 30.9 25.3 Corporate 1,262.7 1,134.4 1,087.9 $ 7,979.6 $ 7,317.0 $ 7,642.5
Revenues by Geography	Revenues by geography as a percentage of total revenues were as follows: Years ended September 30, September 24, September 26, United States 77.6 % 78.9 % 76.0 % Europe 10.0 % 10.2 % 11.8 % Asia-Pacific 8.1 % 7.6 % 8.5 % Rest of world 4.3 % 3.3 % 3.7 % 100.0 % 100.0 % 100.0 %
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]	The Company’s property, plant and equipment, net are geographically located as follows: September 30, 2017 September 24, 2016 September 26, 2015 United States $ 386.5 $ 370.7 $ 369.1 Costa Rica 30.1 28.1 27.7 Europe 57.1 49.2 50.8 Rest of world 17.5 12.2 9.5 $ 491.2 $ 460.2 $ 457.1

Accrued Expenses and Other Lo38

Accrued Expenses and Other Long-Term Liabilities (Tables)	12 Months Ended
	Sep. 30, 2017
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses and other long-term liabilities consisted of the following: September 30, 2017 September 24, 2016 Accrued Expenses Compensation and employee benefits $ 176.7 $ 176.4 Income and other taxes 66.9 38.4 Other 131.7 72.8 $ 375.3 $ 287.6
Schedule of Other Long-Term Liabilities	September 30, 2017 September 24, 2016 Other Long-Term Liabilities Reserve for income tax uncertainties $ 88.3 $ 167.6 Accrued lease obligation—long-term 34.1 34.8 Pension liabilities 10.0 11.2 Other 7.8 10.9 $ 140.2 $ 224.5

Pension and Other Employee Be39

Pension and Other Employee Benefits (Tables)	12 Months Ended
	Sep. 30, 2017
Compensation and Retirement Disclosure [Abstract]
Schedule of Reconciliation of Benefit Obligations, Plan Assets, Funded Status and Related Actuarial Assumptions	The tables below provide a reconciliation of benefit obligations, plan assets, funded status, and related actuarial assumptions of the Company’s German Pension Benefits. Change in Benefit Obligation Years ended September 30, 2017 September 24, 2016 September 26, 2015 Benefit obligation at beginning of year $ (11.0 ) $ (10.0 ) $ (10.3 ) Service cost — — — Interest cost (0.1 ) (0.2 ) (0.3 ) Plan participants’ contributions — — — Actuarial gain (loss) 1.5 (1.2 ) (0.9 ) Foreign exchange gain (0.6 ) 0.1 1.2 Benefits paid 0.3 0.3 0.3 Benefit obligation at end of year (9.9 ) (11.0 ) (10.0 ) Plan assets — — — Benefit obligation at end of year $ (9.9 ) $ (11.0 ) $ (10.0 )
Components of Net Periodic Benefit Cost and Related Actuarial Assumptions	The tables below outline the components of the net periodic benefit cost and related actuarial assumptions of the Company’s German Pension Benefits. Components of Net Periodic Benefit Cost Years ended September 30, 2017 September 24, 2016 September 26, 2015 Service cost $ — $ — $ — Interest cost 0.1 0.4 0.3 Expected return on plan assets — — — Amortization of prior service cost — — Recognized net actuarial gain 0.4 (0.2 ) — Net periodic benefit cost $ 0.5 $ 0.2 $ 0.3
Schedule of Weighted-Average Net Periodic Benefit Cost Assumptions	Weighted-Average Net Periodic Benefit Cost Assumptions 2017 2016 2015 Discount rate 2.15 % 1.30 % 2.05 % Expected return on plan assets — % — % — % Rate of compensation increase — % — % — %
Schedule of Expected Pension Benefit	The table below reflects the total Pension Benefits expected to be paid for the German Pension Benefits each fiscal year as of September 30, 2017 : 2018 $ 0.4 2019 $ 0.4 2020 $ 0.4 2021 $ 0.4 2022 $ 0.4 2023 to 2027 $ 2.2

Quarterly Statement of Operat40

Quarterly Statement of Operations Information (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Results of Operations	The following table presents a summary of quarterly results of operations for fiscal 2017 and 2016 : 2017 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenue $ 734.4 $ 715.4 $ 806.1 $ 802.9 Gross profit 404.8 388.7 409.6 417.9 Net income (1) 86.5 526.8 59.5 82.7 Diluted net income per common share $ 0.30 $ 1.84 $ 0.21 $ 0.29 2016 First Quarter Second Quarter Third Quarter Fourth Quarter Total revenue $ 695.2 $ 693.3 $ 717.4 $ 726.8 Gross profit 379.1 385.0 393.1 406.1 Net income (2) 84.9 68.9 84.8 92.2 Diluted net income per common share $ 0.29 $ 0.24 $ 0.30 $ 0.33 (1) Net income in the first quarter of fiscal 2017 included restructuring charges of $3.2 million and acquisition charges of $2.6 million . Net income in the second quarter of fiscal 2017 included a gain on the sale of the blood screening business of $899.7 million , acquisition charges of $19.4 million , and restructuring charges of $1.6 million . Net income in the third quarter of fiscal 2017 included restructuring charges of $6.0 million and a debt extinguishment loss of $2.6 million . Net income in the fourth quarter of fiscal 2017 included restructuring charges of $2.5 million , and gain on sale of cost method investment of $2.0 million . (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.

Operations (Details)

Operations (Details)	Mar. 22, 2017Segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	5

Summary of Significant Accoun42

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended						12 Months Ended
	Apr. 01, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 24, 2016USD ($)Customer	Mar. 26, 2016USD ($)	Dec. 26, 2015USD ($)	Sep. 26, 2015USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)Customer	Sep. 24, 2016USD ($)Customer	Sep. 26, 2015USD ($)	Jul. 02, 2017USD ($)	Jul. 01, 2017USD ($)	Apr. 07, 2017USD ($)	Mar. 22, 2017USD ($)	Jun. 25, 2016USD ($)
Significant Accounting Policies [Line Items]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense								$ 10,300,000
Marketable Securities, Unrealized Gain (Loss)		$ 4,000,000
Cash equivalent maturity period								three months or less
Net (gains) losses reclassified from accumulated other comprehensive income to the statement of income					$ 7,200,000			$ 2,400,000	$ 6,100,000	$ 0
Equity investment impairment charges								$ 0	$ 1,100,000	7,800,000
Number of customers with balance greater than specified percentage | Customer			0					0	0
Accumulated Amortization			$ 2,681,500,000					$ 2,742,100,000	$ 2,681,500,000
Indefinite-lived Intangible Assets Acquired				$ 4,800,000
Sensitivity Change To Fair Value By Percent								10.00%
Goodwill			2,803,100,000					$ 3,171,200,000	2,803,100,000
Other-than-temporary impairment charges									0
Purchase of interest rate caps								1,900,000	0	13,200,000
Principal amount of borrowings								1,000,000,000
Loss reclassified from accumulated other comprehensive income to the statement of operations, net								6,900,000	3,900,000	0
Derivative Instruments, Gain (Loss) Reclassification from Accumulated OCI to Income, Estimated Net Amount to be Transferred								3,600,000
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments								3,100,000	1,500,000
Unrealized Gain (Loss) on Foreign Currency Derivatives, Net, before Tax								3,600,000	1,100,000
Notional Amount								$ 209,000,000
Product Warranty Term								1 year
Advertising cost								$ 22,500,000	20,200,000	14,400,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax								4,500,000	(2,200,000)
Increase to cash flows provided by operations								8,300,000	798,200,000	796,800,000
Increase to cash flows used in financing activities								(285,800,000)	68,400,000	$ 86,100,000
MRI Breast Coils [Member]
Significant Accounting Policies [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									9,600,000
Developed Technology Rights [Member]
Significant Accounting Policies [Line Items]
Accumulated Amortization			1,991,600,000					2,186,800,000	1,991,600,000
Developed Technology Rights [Member] | Cystic Fibrosis [Member]
Significant Accounting Policies [Line Items]
Accumulated Amortization															$ 6,200,000
Trade Names [Member]
Significant Accounting Policies [Line Items]
Accumulated Amortization			141,600,000					$ 156,400,000	$ 141,600,000
Minimum
Significant Accounting Policies [Line Items]
Intangible assets useful life								2 years
Defined contract term								3 years
Transition services agreement term	2 years
Minimum | Accounts receivable [Member]
Significant Accounting Policies [Line Items]
Concentration risk, percentage								10.00%	10.00%
Minimum | Total revenues [Member]
Significant Accounting Policies [Line Items]
Concentration risk, percentage								10.00%	10.00%	10.00%
Maximum
Significant Accounting Policies [Line Items]
Intangible assets useful life								30 years
Defined contract term								5 years
Transition services agreement term	3 years
Other Nonoperating Income (Expense) [Member]
Significant Accounting Policies [Line Items]
Gain on Sale of Investments	$ 3,800,000
Interest Rate Cap [Member]
Significant Accounting Policies [Line Items]
Interest rate caps - derivative			1,400,000					$ 4,800,000	$ 1,400,000
Equity Securities [Member]
Significant Accounting Policies [Line Items]
Realized Gain (Loss) on Marketable Securities, Cost Method Investments, and Other Investments					$ (25,100,000)
Equity investment impairment charges			1,100,000			$ 7,800,000		0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									(7,800,000)
Cynosure [Member]
Significant Accounting Policies [Line Items]
Intangible assets	994,000,000
Accelerated depreciation of acquired software								3,000,000
Short and long-term marketable securities assumed														$ 82,900,000
Goodwill														$ 683,500,000
Medicor Medical Supply
Significant Accounting Policies [Line Items]
Intangible assets												$ 5,400,000	$ 5,400,000
Goodwill													$ 8,900,000
Gen-Probe Incorporated [Member] | Developed Technology Rights [Member]
Significant Accounting Policies [Line Items]
Intangible assets												$ 3,700,000
Scenario, Forecast [Member] | Cynosure [Member]
Significant Accounting Policies [Line Items]
Accelerated depreciation of acquired software							$ 5,900,000
Discontinued Operations, Disposed of by Sale [Member] | Blood Screening Business | Developed Technology Rights [Member]
Significant Accounting Policies [Line Items]
Disposal Group, Including Discontinued Operation, Intangible Assets	154,000,000
Discontinued Operations, Disposed of by Sale [Member] | Blood Screening Business | Customer relationships
Significant Accounting Policies [Line Items]
Disposal Group, Including Discontinued Operation, Intangible Assets	$ 387,700,000
Medical Aesthetics [Member]
Significant Accounting Policies [Line Items]
Goodwill			$ 0					683,500,000	0		$ 683,500,000
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount											2.00%
Operating Segments [Member]
Significant Accounting Policies [Line Items]
Goodwill								$ 2,490,000,000
Accounting Standards Update 2016-09 [Member]
Significant Accounting Policies [Line Items]
Increase to cash flows provided by operations									11,000,000	$ 10,700,000
Increase to cash flows used in financing activities									$ 11,000,000	$ 10,700,000
Forward foreign currency contracts
Significant Accounting Policies [Line Items]
Derivative contract period, or less								1 year

Summary of Significant Accoun43

Summary of Significant Accounting Policies - Summary of Marketable Securities (Detail) - Equity securities - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Schedule Of Marketable Securities [Line Items]
Cost	$ 0.7	$ 2.4	$ 16.1
Gross Unrealized Gains	0	0	7.2
Gross Unrealized Losses	(0.6)	(0.3)	(0.3)
Other than temporary impairment	0	(1.1)	(7.8)
Fair Value	$ 0.1	$ 1	$ 15.2

Summary of Significant Accoun44

Summary of Significant Accounting Policies - Supplemental Cash Flow Statement Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Accounting Policies [Abstract]
Cash paid during the period for income taxes	$ 867.8	$ 184.8	$ 168.7
Cash paid during the period for interest	$ 102.4	$ 104	$ 143

Summary of Significant Accoun45

Summary of Significant Accounting Policies - Schedule of Inventories (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Accounting Policies [Abstract]
Raw materials	$ 95.7	$ 96.4
Work-in-process	45	51.7
Finished goods	190.9	126.6
Inventories	$ 331.6	$ 274.7

Summary of Significant Accoun46

Summary of Significant Accounting Policies - Estimated Useful Lives of Property, Plant and Equipments (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Property, Plant and Equipment [Line Items]
Manufacturing Equipment And Software	$ 422.4	$ 381.9
Equipment Under Customer Usage Agreements	368.7	334.6
Buildings and Improvements, Gross	172	186.1
Leasehold Improvements, Gross	60.6	65.6
Land	46.3	51.9
Furniture and Fixtures, Gross	20.8	18.4
Property, Plant and Equipment, Gross	1,090.8	1,038.5
Less - accumulated depreciation and amortization	(599.6)	(578.3)
Property, plant and equipment, net	$ 491.2	$ 460.2	$ 457.1
Building and Improvements [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful life	20 years
Building and Improvements [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful life	35 years
Equipment and Software [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful life	3 years
Equipment and Software [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful life	10 years
Equipment Under Customer Usage Agreements [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful life	3 years
Equipment Under Customer Usage Agreements [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful life	8 years
Furniture and Fixtures [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful life	5 years
Furniture and Fixtures [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful life	7 years

Summary of Significant Accoun47

Summary of Significant Accounting Policies - Schedule of Intangible Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 5,483.7	$ 5,324.9
Accumulated Amortization	2,742.1	2,681.5
Developed technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	4,528.7	3,983.7
Accumulated Amortization	2,186.8	1,991.6
In-process research and development
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	46	3.7
Accumulated Amortization	0	0
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	552.8	1,098.9
Accumulated Amortization	393.8	546.2
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	310.3	236.2
Accumulated Amortization	156.4	141.6
Distribution agreement
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	42	0
Accumulated Amortization	2.8	0
Non-competition agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	1.5	0
Accumulated Amortization	0.1	0
Business licenses
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Value	2.4	2.4
Accumulated Amortization	$ 2.2	$ 2.1

Summary of Significant Accoun48

Summary of Significant Accounting Policies - Schedule of Estimated Amortization Expense (Detail) $ in Millions	Sep. 30, 2017USD ($)
Accounting Policies [Abstract]
Fiscal 2,018	$ 376.6
Fiscal 2,019	364.9
Fiscal 2,020	353.6
Fiscal 2,021	332.2
Fiscal 2,022	$ 319.8

Summary of Significant Accoun49

Summary of Significant Accounting Policies - Rollforward of Goodwill Activity by Reportable Segments (Detail) $ in Thousands	12 Months Ended
	Sep. 30, 2017USD ($)
Goodwill [Roll Forward]
Balance at September 24, 2016	$ 2,803,100
Acquisitions	692,400
Sale of blood screening business	(325,000)
Foreign currency and other adjustments	700
Balance at September 30, 2017	3,171,200
Diagnostics
Goodwill [Roll Forward]
Balance at September 24, 2016	1,148,200
Acquisitions	0
Sale of blood screening business	(325,000)
Foreign currency and other adjustments	(200)
Balance at September 30, 2017	823,000
Breast Health
Goodwill [Roll Forward]
Balance at September 24, 2016	631,800
Acquisitions	8,900
Sale of blood screening business	0
Foreign currency and other adjustments	800
Balance at September 30, 2017	641,500
Medical Aesthetics
Goodwill [Roll Forward]
Balance at September 24, 2016	0
Acquisitions	683,500
Sale of blood screening business	0
Foreign currency and other adjustments	0
Balance at September 30, 2017	683,500
GYN Surgical
Goodwill [Roll Forward]
Balance at September 24, 2016	1,015,000
Acquisitions	0
Sale of blood screening business	0
Foreign currency and other adjustments	100
Balance at September 30, 2017	1,015,100
Skeletal Health
Goodwill [Roll Forward]
Balance at September 24, 2016	8,100
Acquisitions	0
Sale of blood screening business	0
Foreign currency and other adjustments	0
Balance at September 30, 2017	$ 8,100

Summary of Significant Accoun50

Summary of Significant Accounting Policies - Schedule of Other Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Accounting Policies [Abstract]
Life insurance contracts	$ 41	$ 36
Capitalized software	12.3	10
Manufacturing access fees	7.1	9.6
Cost-method equity investments	3	3.5
Deferred tax assets	9.1	9.3
Other	24.5	15.3
Other assets	$ 97	$ 83.7

Summary of Significant Accoun51

Summary of Significant Accounting Policies - Changes in accumulated balances of other comprehensive income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	$ (18.5)	$ (26.1)	$ (15.7)
Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(0.4)	(0.3)	6.9
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	1.6	2.5	1.8
Accumulated other comprehensive Income loss Hedge	4.3	(3.4)	(3.9)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(16.2)	(32.3)	(14.5)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent	7.6	(10.4)	(20.6)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(2.3)	1.1	9.8
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax, Portion Attributable to Parent	(0.9)	0.7	$ 0.2
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	0.8	(3.4)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	11.6	(15.6)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	4.5	(2.2)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Pension in Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Equity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2.4)	(6.1)
Interest Rate Cap [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 6.9	$ 3.9

Summary of Significant Accoun52

Summary of Significant Accounting Policies - Schedule of Derivative Instruments on the Consolidated Balance Sheets (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$ 0.8	$ (3.4)
Interest rate caps - derivative
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cash Flow Hedge Derivative Instrument Assets at Fair Value	4.8	1.4
Interest rate caps - derivative | Prepaid Expenses and Other Current Assets [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cash Flow Hedge Derivative Instrument Assets at Fair Value	3.6	1
Interest rate caps - derivative | Other Assets [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cash Flow Hedge Derivative Instrument Assets at Fair Value	1.2	0.4
Forward foreign currency contracts | Prepaid Expenses and Other Current Assets [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cash Flow Hedge Derivative Instrument Assets at Fair Value	0.4	0.2
Forward foreign currency contracts | Accrued Liabilities [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cash Flow Hedge Derivative Instrument Assets at Fair Value	$ 4	$ 1.3

Summary of Significant Accoun53

Summary of Significant Accounting Policies - Amount of loss recognized in other comprehensive income, net of taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 4.5	$ (2.2)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	0.8	(3.4)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Equity securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2.4)	(6.1)
Interest rate caps - derivative
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 6.9	$ 3.9

Summary of Significant Accoun54

Summary of Significant Accounting Policies - Schedule of Unrealized Loss Recognized in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Accounting Policies [Abstract]
Loss recognized in other comprehensive income, net	$ 0.8	$ (3.4)	$ (3.9)

Summary of Significant Accoun55

Summary of Significant Accounting Policies - Accounts Receivable Reserve Activity (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at Beginning of Period	$ 12.7	$ 11.1	$ 12
Charged to Costs and Expenses	1.8	2	1.6
Write- offs and Payments	(4.7)	(0.4)	(2.5)
Balance at End of Period	$ 9.8	$ 12.7	$ 11.1

Summary of Significant Accoun56

Summary of Significant Accounting Policies - Reconciliation of Basic and Diluted Share Amounts (Detail) - shares shares in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Earnings Per Share [Line Items]
Basic weighted average common shares outstanding (in shares)	279,811	280,213	280,566
Weighted Average Common Stock Equivalents From Assumed Exercise Of Stock Options And Restricted Stock Units	2,885	2,631	2,898
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	2,957	3,312	6,073
Diluted weighted average common shares outstanding (in shares)	285,653	286,156	289,537
Outstanding Stock Options [Member]
Weighted-average anti-dilutive shares related to:
Weighted-average anti-dilutive shares (in shares)	1,677	1,029	1,502
Restricted Stock Units [Member]
Weighted-average anti-dilutive shares related to:
Weighted-average anti-dilutive shares (in shares)	12	62	49

Summary of Significant Accoun57

Summary of Significant Accounting Policies - Product Warranty (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at Beginning of Period	$ 5	$ 5.4
Acquired	9.9	0
Provisions	15.3	7.1
Settlements/ Adjustments	(13.2)	(7.5)
Balance at End of Period	$ 17	$ 5

Business Combinations - Narrati

Business Combinations - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions

Apr. 07, 2017

Mar. 22, 2017

Sep. 30, 2017

Jul. 01, 2017

Apr. 01, 2017

Dec. 31, 2016

Sep. 24, 2016

Jun. 25, 2016

Mar. 26, 2016

Dec. 26, 2015

Sep. 30, 2017

Sep. 30, 2017

Sep. 24, 2016

Sep. 26, 2015

Business Acquisition [Line Items]

Revenues

$ 802.9

$ 806.1

$ 715.4

$ 734.4

$ 726.8

$ 717.4

$ 693.3

$ 695.2

$ 3,058.8

$ 2,832.7

$ 2,705

Pre-tax loss

(1,370.2)

(548.6)

$ (455.1)

Goodwill

3,171.2

$ 2,803.1

$ 3,171.2

$ 3,171.2

$ 2,803.1

Cynosure

Business Acquisition [Line Items]

Purchase price (in dollars per share)

$ 66

Outstanding noncontrolling shares (in shares)

1.2

Total purchase price

$ 1,660

Transaction costs

18.8

Intangible assets

$ 994

Revenues

207.5

Pre-tax loss

$ 96.4

Goodwill

683.5

Property, plant and equipment

44.1

Cynosure | In-process research and development

Business Acquisition [Line Items]

Intangible assets

107

Estimated costs to complete

$ 18

Cynosure | Developed technology

Business Acquisition [Line Items]

Project fair value

61

Estimated cost to complete project

$ 4

Weighted average period

11 years 9 months 18 days

Cynosure | Distribution agreement

Business Acquisition [Line Items]

Weighted average period

8 years

Cynosure | Customer relationships

Business Acquisition [Line Items]

Weighted average period

7 years 8 months 12 days

Cynosure | Trade names

Business Acquisition [Line Items]

Weighted average period

8 years 10 months 24 days

Cynosure | Minimum | Other intangible assets

Business Acquisition [Line Items]

Discount rate (as a percent)

11.00%

Cynosure | Minimum | In-process research and development

Business Acquisition [Line Items]

Discount rate (as a percent)

14.00%

Cynosure | Maximum | Other intangible assets

Business Acquisition [Line Items]

Discount rate (as a percent)

12.00%

Cynosure | Maximum | In-process research and development

Business Acquisition [Line Items]

Discount rate (as a percent)

22.00%

Medicor Medical Supply

Business Acquisition [Line Items]

Cash paid

$ 19

Intangible assets

$ 5.4

$ 5.4

Weighted average period

7 years 8 months 12 days

Acquisition price adjustment

$ 2

Purchase price withheld

1.9

Goodwill

8.9

Property, plant and equipment

$ 4.7

Business Combinations - Purchas

Business Combinations - Purchase Price Allocation (Details) - USD ($) $ in Millions	Sep. 30, 2017	Mar. 22, 2017	Sep. 24, 2016
Business Acquisition [Line Items]
Goodwill	$ 3,171.2		$ 2,803.1
Cynosure
Business Acquisition [Line Items]
Cash		$ 107.2
Marketable securities		82.9
Accounts receivable		40.2
Inventory		121.1
Property, plant and equipment		44.1
Other assets and liabilities, net		12.2
Accounts payable and accrued expenses		(75.3)
Deferred revenue		(11.2)
Capital lease obligation		(25.2)
Deferred income taxes, net		(315.7)
Goodwill		683.5
Purchase Price		1,657.8
Cynosure | Developed technology
Business Acquisition [Line Items]
Identifiable intangible assets		736
Cynosure | In-process research and development
Business Acquisition [Line Items]
Identifiable intangible assets		107
Cynosure | Distribution agreement
Business Acquisition [Line Items]
Identifiable intangible assets		42
Cynosure | Customer relationships
Business Acquisition [Line Items]
Identifiable intangible assets		35
Cynosure | Trade names
Business Acquisition [Line Items]
Identifiable intangible assets		$ 74

Business Combinations Business

Business Combinations Business Combinations - Pro Forma (Details) - Cynosure - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016
Business Acquisition [Line Items]
Revenue	$ 3,241.4	$ 3,244.6
Net income	$ 768.5	$ 252.3
Basic earnings per common share (in dollars per share)	$ 2.75	$ 0.90
Diluted earnings per common share (in dollars per share)	$ 2.69	$ 0.88

Restructuring and Divestiture61

Restructuring and Divestiture Charges - Charges Taken Related to Restructuring Actions (Detail) - USD ($) $ in Millions	3 Months Ended							12 Months Ended
	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 24, 2016	Mar. 26, 2016	Dec. 26, 2015	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Restructuring Cost and Reserve [Line Items]
Fiscal restructuring and divestiture charges	$ 2.5	$ 6	$ 1.6	$ 3.2	$ 2.9	$ 3.8	$ 2.3	$ 13.3	$ 10.5	$ 28.5
Fiscal 2015 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions										16.3
Facility closure costs										2.6
Fiscal restructuring charges										18.9
Divestiture net charges										9.6
Fiscal restructuring and divestiture charges										28.5
Fiscal 2016 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions									10.5
Fiscal restructuring charges									10.5
Two Thousand Seventeen [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions								8.5
Facility closure costs								4.8
Other								0
Fiscal restructuring charges								13.3
Fiscal 2017 Actions [Member] | Fiscal 2015 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions										0
Facility closure costs										0
Fiscal restructuring charges										0
Fiscal 2017 Actions [Member] | Fiscal 2016 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions									0
Fiscal restructuring charges									0
Fiscal 2017 Actions [Member] | Two Thousand Seventeen [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions								8.5
Facility closure costs								0
Other								0
Fiscal restructuring charges								8.5
Fiscal 2016 Actions [Domain] | Fiscal 2015 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions										0
Facility closure costs										0
Fiscal restructuring charges										0
Fiscal 2016 Actions [Domain] | Fiscal 2016 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions									10.5
Fiscal restructuring charges									10.5
Fiscal 2016 Actions [Domain] | Two Thousand Seventeen [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions								0
Facility closure costs								4.8
Other								0
Fiscal restructuring charges								4.8
Fiscal 2015 Actions [Member] | Fiscal 2015 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions										10
Facility closure costs										0
Fiscal restructuring charges										10
Fiscal 2015 Actions [Member] | Fiscal 2016 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions									0
Fiscal restructuring charges									0
Fiscal 2015 Actions [Member] | Two Thousand Seventeen [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions								0
Facility closure costs								0
Other								0
Fiscal restructuring charges								0
Fiscal 2014 Actions [Member] | Fiscal 2015 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions										6
Facility closure costs										2
Fiscal restructuring charges										8
Fiscal 2014 Actions [Member] | Fiscal 2016 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions									0
Fiscal restructuring charges									0
Fiscal 2014 Actions [Member] | Two Thousand Seventeen [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions								0
Facility closure costs								0
Other								0
Fiscal restructuring charges								0
Other Operating Cost Reductions [Member] | Fiscal 2015 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions										0.3
Facility closure costs										0.6
Fiscal restructuring charges										$ 0.9
Other Operating Cost Reductions [Member] | Fiscal 2016 Charges [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions									0
Fiscal restructuring charges									$ 0
Other Operating Cost Reductions [Member] | Two Thousand Seventeen [Member] | Restructuring Charges [Member]
Restructuring Cost and Reserve [Line Items]
Workforce reductions								0
Facility closure costs								0
Other								0
Fiscal restructuring charges								$ 0

Restructuring and Divestiture62

Restructuring and Divestiture Charges - Charges Taken Related to Accrued Restructuring Actions (Detail) - Restructuring Charges [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Two Thousand Seventeen [Member]
Restructuring Reserve [Roll Forward]
Fiscal restructuring charges	$ 13.3
Severance payments	(6.6)
Other payments	(1.5)
Balance	11.5
Two Thousand Seventeen [Member] | Fiscal 2017 Actions [Member]
Restructuring Reserve [Roll Forward]
Fiscal restructuring charges	8.5
Severance payments	(1)
Other payments	0
Balance	7.5
Two Thousand Seventeen [Member] | Fiscal 2016 Actions [Domain]
Restructuring Reserve [Roll Forward]
Fiscal restructuring charges	4.8
Severance payments	(5.4)
Other payments	(1.2)
Balance	3.7
Two Thousand Seventeen [Member] | Fiscal 2015 Actions [Member]
Restructuring Reserve [Roll Forward]
Fiscal restructuring charges	0
Severance payments	(0.2)
Other payments	0
Balance	0
Two Thousand Seventeen [Member] | Fiscal 2014 Actions [Member]
Restructuring Reserve [Roll Forward]
Fiscal restructuring charges	0
Severance payments	0
Other payments	(0.3)
Balance	0.3
Two Thousand Seventeen [Member] | Other Operating Cost Reductions [Member]
Restructuring Reserve [Roll Forward]
Fiscal restructuring charges	0
Severance payments	0
Other payments	0
Balance	0
Fiscal 2016 Charges [Member]
Restructuring Reserve [Roll Forward]
Balance	6.3
Fiscal restructuring charges		$ 10.5
Stock-based compensation		(0.4)
Severance payments		(9)
Other payments		(0.5)
Balance		6.3
Fiscal 2016 Charges [Member] | Fiscal 2017 Actions [Member]
Restructuring Reserve [Roll Forward]
Balance	0
Fiscal restructuring charges		0
Stock-based compensation		0
Severance payments		0
Other payments		0
Balance		0
Fiscal 2016 Charges [Member] | Fiscal 2016 Actions [Domain]
Restructuring Reserve [Roll Forward]
Balance	5.5
Fiscal restructuring charges		10.5
Stock-based compensation		(0.4)
Severance payments		(4.6)
Other payments		0
Balance		5.5
Fiscal 2016 Charges [Member] | Fiscal 2015 Actions [Member]
Restructuring Reserve [Roll Forward]
Balance	0.2
Fiscal restructuring charges		0
Stock-based compensation		0
Severance payments		(2.9)
Other payments		0
Balance		0.2
Fiscal 2016 Charges [Member] | Fiscal 2014 Actions [Member]
Restructuring Reserve [Roll Forward]
Balance	0.6
Fiscal restructuring charges		0
Stock-based compensation		0
Severance payments		(1.4)
Other payments		(0.5)
Balance		0.6
Fiscal 2016 Charges [Member] | Other Operating Cost Reductions [Member]
Restructuring Reserve [Roll Forward]
Balance	$ 0
Fiscal restructuring charges		0
Stock-based compensation		0
Severance payments		(0.1)
Other payments		0
Balance		0
Fiscal 2015 Charges [Member]
Restructuring Reserve [Roll Forward]
Balance		5.7
Fiscal restructuring charges			$ 18.9
Stock-based compensation			(4.1)
Severance payments			(23.9)
Other payments			(2.1)
Balance			5.7
Fiscal 2015 Charges [Member] | Fiscal 2017 Actions [Member]
Restructuring Reserve [Roll Forward]
Balance		0
Fiscal restructuring charges			0
Stock-based compensation			0
Severance payments			0
Other payments			0
Balance			0
Fiscal 2015 Charges [Member] | Fiscal 2016 Actions [Domain]
Restructuring Reserve [Roll Forward]
Balance		0
Fiscal restructuring charges			0
Stock-based compensation			0
Severance payments			0
Other payments			0
Balance			0
Fiscal 2015 Charges [Member] | Fiscal 2015 Actions [Member]
Restructuring Reserve [Roll Forward]
Balance		3.1
Fiscal restructuring charges			10
Stock-based compensation			(4.1)
Severance payments			(2.8)
Other payments			0
Balance			3.1
Fiscal 2015 Charges [Member] | Fiscal 2014 Actions [Member]
Restructuring Reserve [Roll Forward]
Balance		2.5
Fiscal restructuring charges			8
Stock-based compensation			0
Severance payments			(16.2)
Other payments			(1.3)
Balance			2.5
Fiscal 2015 Charges [Member] | Other Operating Cost Reductions [Member]
Restructuring Reserve [Roll Forward]
Balance		$ 0.1
Fiscal restructuring charges			0.9
Stock-based compensation			0
Severance payments			(4.9)
Other payments			(0.8)
Balance			0.1
Fiscal 2014 Charges [Member]
Restructuring Reserve [Roll Forward]
Balance			16.9
Fiscal 2014 Charges [Member] | Fiscal 2017 Actions [Member]
Restructuring Reserve [Roll Forward]
Balance			0
Fiscal 2014 Charges [Member] | Fiscal 2016 Actions [Domain]
Restructuring Reserve [Roll Forward]
Balance			0
Fiscal 2014 Charges [Member] | Fiscal 2015 Actions [Member]
Restructuring Reserve [Roll Forward]
Balance			0
Fiscal 2014 Charges [Member] | Fiscal 2014 Actions [Member]
Restructuring Reserve [Roll Forward]
Balance			12
Fiscal 2014 Charges [Member] | Other Operating Cost Reductions [Member]
Restructuring Reserve [Roll Forward]
Balance			$ 4.9

Restructuring and Divestiture63

Restructuring and Divestiture Charges - Additional Information (Detail) - USD ($) $ in Millions

3 Months Ended

12 Months Ended

Sep. 30, 2017

Jul. 01, 2017

Apr. 01, 2017

Dec. 31, 2016

Sep. 24, 2016

Jun. 27, 2015

Sep. 27, 2014

Dec. 28, 2013

Sep. 30, 2017

Sep. 24, 2016

Sep. 26, 2015

Sep. 27, 2014

Restructuring Cost and Reserve [Line Items]

Gain on sale of business

$ 5.3

$ 899.7

$ 0

$ 0

Restructuring reserve, translation adjustment

$ 9.6

Cynosure

Restructuring Cost and Reserve [Line Items]

Severance charges

$ 1.3

$ 4.3

$ 1.5

Bedford [Member]

Restructuring Cost and Reserve [Line Items]

Facility closure costs

$ 1.3

$ 3.5

Fiscal 2014 Actions [Member]

Restructuring Cost and Reserve [Line Items]

Severance charges

$ 6.3

$ 16.6

Compensation charges

$ 1.8

Fiscal 2014 Actions [Member] | Jack Cumming [Member]

Restructuring Cost and Reserve [Line Items]

Severance charges

6.6

Compensation charges

$ 4.4

Restructuring Charges [Member] | San Diego [Member]

Restructuring Cost and Reserve [Line Items]

Severance charges

$ 1.4

$ 0.9

Restructuring Charges [Member] | Bedford [Member]

Restructuring Cost and Reserve [Line Items]

Severance charges

1.7

Restructuring Charges [Member] | International [Member]

Restructuring Cost and Reserve [Line Items]

Severance charges

$ 7.9

Restructuring Charges [Member] | Fiscal 2015 Charges [Member]

Restructuring Cost and Reserve [Line Items]

Facility closure costs

2.6

Workforce reductions

16.3

Restructuring Charges [Member] | Fiscal 2015 Actions [Member] | Fiscal 2015 Charges [Member]

Restructuring Cost and Reserve [Line Items]

Severance charges

$ 0

Facility closure costs

0

Workforce reductions

10

Compensation charges

4.1

Restructuring Charges [Member] | Fiscal 2014 Actions [Member] | Fiscal 2015 Charges [Member]

Restructuring Cost and Reserve [Line Items]

Facility closure costs

2

Workforce reductions

$ 6

Number of office locations

0

Borrowings and Credit Arrange64

Borrowings and Credit Arrangements - Company's Borrowings (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Debt Instrument [Line Items]
Current debt obligations, net of debt discount	$ 1,150.8	$ 296
Convertible Notes	484.5	12.2
Convertible Notes	0	763.5
Total long-term debt obligations	2,172.1	3,049.4
Total debt obligations	3,322.9	3,345.4
Term Loan
Debt Instrument [Line Items]
Current debt obligations, net of debt discount	121.3	83.8
Long-term debt obligations, net of debt discount	1,190.5	1,308.2
Revolver
Debt Instrument [Line Items]
Current debt obligations, net of debt discount	345	0
Securitization Program
Debt Instrument [Line Items]
Current debt obligations, net of debt discount	200	200
2022 Senior Notes
Debt Instrument [Line Items]
Long-term debt obligations, net of debt discount	$ 981.6	$ 977.7

Borrowings and Credit Arrange65

Borrowings and Credit Arrangements - Debt Maturity Schedule for Components of Company's Obligations (Details) $ in Millions	Sep. 30, 2017USD ($)
Debt Instrument [Line Items]
2,018	$ 1,155.2
2,019	150
2,020	1,050
2,021	0
2,022	1,000
2023 and Thereafter	0
Total	3,355.2
Term Loan
Debt Instrument [Line Items]
2,018	121.9
2,019	150
2,020	1,050
2,021	0
2,022	0
2023 and Thereafter	0
Total	1,321.9
Revolver
Debt Instrument [Line Items]
2,018	345
2,019	0
2,020	0
2,021	0
2,022	0
2023 and Thereafter	0
Total	345
Securitization Program
Debt Instrument [Line Items]
2,018	200
2,019	0
2,020	0
2,021	0
2,022	0
2023 and Thereafter	0
Total	200
2022 Senior Notes
Debt Instrument [Line Items]
2,018	0
2,019	0
2,020	0
2,021	0
2,022	1,000
2023 and Thereafter	0
Total	1,000
Convertible Notes
Debt Instrument [Line Items]
2,018	488.3
2,019
2,020	0
2,021	0
2,022	0
2023 and Thereafter	0
Total	$ 488.3

Borrowings and Credit Arrange66

Borrowings and Credit Arrangements - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions	Nov. 14, 2017	Oct. 10, 2017	Dec. 19, 2016	Nov. 09, 2016	May 29, 2015	Dec. 24, 2014	Feb. 14, 2013	Feb. 29, 2012	Dec. 10, 2007	Sep. 30, 2017	Jul. 01, 2017	Dec. 31, 2016	Sep. 24, 2016	Mar. 26, 2016	Dec. 26, 2015	Sep. 26, 2015	Jun. 27, 2015	Dec. 25, 2010	Apr. 01, 2017	Jul. 01, 2015	Jun. 27, 2015	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015	Oct. 31, 2017	Apr. 21, 2017	Aug. 01, 2015	Jul. 02, 2015	Aug. 01, 2012	Nov. 18, 2010
Debt Instrument [Line Items]
Notes principal amount											$ 100,000,000
Amount borrowed under revolver										$ 345,000,000												$ 345,000,000
Non-cash interest expense amortization of debt discount and deferred financing costs																						49,400,000	$ 52,100,000	$ 63,800,000
Debt extinguishment loss										(600,000)	2,600,000		$ 800,000	$ 4,500,000								3,200,000	5,300,000	62,700,000
Payment of debt issuance costs																						0	0	(22,700,000)
Repurchase of common stock										200,100,000												200,100,000
Amount repaid under revolver																						175,000,000
Principal amount of borrowings										$ 1,000,000,000												1,000,000,000
Repayments of convertible debt											269,100,000	$ 12,300,000										396,200,000	392,800,000	543,700,000
Conversion premium																			$ 8,700,000
Adjustments to APIC, equity component of convertible debt																						$ (33,900,000)	$ (94,400,000)	$ (216,900,000)
Penalty fee percentage										0.25%												0.25%
Maximum number of shares subject to mandatory redemption (in shares)										18												18
Period to remedy event of default																						90 days
Accretion expense											$ 18,500,000
2013 Notes
Debt Instrument [Line Items]
Notes principal amount										$ 68,000,000												$ 68,000,000
Debt extinguishment loss																						$ (2,300,000)
Repayments of convertible debt										82,900,000
Conversion price (in dollars per share)											$ 38.590
Accretion expense										13,300,000
Credit Agreement
Debt Instrument [Line Items]
Notes principal amount																													$ 2,800,000,000
Proceeds under credit agreement					$ 1,680,000,000
Credit agreement interest rate																						2.39%	2.08%	2.43%
Interest expense																						$ 42,300,000	$ 40,400,000	$ 54,700,000
Non-cash interest expense amortization of debt discount and deferred financing costs																						$ 4,200,000	4,400,000	9,000,000
Leverage ratio maximum																						5.50
Interest coverage ratio																						3.75
Decreased net leverage ratio																						4
Debt extinguishment loss																	$ 18,200,000
Number of debt instruments																	2
Maximum range of present value of cash flow, percentage																	10.00%
Third-party costs																	$ 4,600,000
Payment of debt issuance costs																	(3,800,000)
Fees recorded as debt discount																	$ 4,900,000
Principal amount of borrowings										$ 1,670,000,000												$ 1,670,000,000							$ 2,500,000,000
Credit Agreement | Percentage Added to Eurodollar Rate [Member]
Debt Instrument [Line Items]
Basis spread on variable rate					1.50%
Term Loan
Debt Instrument [Line Items]
Credit agreement interest rate																						2.73%
Senior Notes
Debt Instrument [Line Items]
Interest expense																						$ 57,300,000	56,000,000	67,200,000
Non-cash interest expense amortization of debt discount and deferred financing costs																						3,900,000	$ 3,800,000	2,100,000
Debt extinguishment loss													$ 22,300,000
Interest rate during period																				6.25%
Long-term debt obligations																												$ 1,000,000,000
Final interest payment																											$ 31,250,000
2022 Notes [Member]
Debt Instrument [Line Items]
Interest rate during period																							5.25%
Long-term debt obligations																												$ 1,000,000,000
Offering price, percentage of principal amount																												100.00%
Debt instrument, maturity period																							2,022
Percentage of redemption price																												100.00%
Maximum percentage of redemption of senior notes																												35.00%
Percentage of redemption price, second period																												105.25%
Percentage of redemption price, third period																												102.625%
Percentage of redemption price, fourth period																												101.313%
Percentage of redemption price, fifth period																												100.00%
Percentage price of principal amount for repurchase of senior note													101.00%
Convertible Notes
Debt Instrument [Line Items]
Debt extinguishment loss													$ 15,500,000
Deferred taxes, reacquisition of equity component													29,200,000
Cash per original principle amount																						$ 1,000
Adjustments to APIC, equity component of convertible debt													246,100,000
Convertible Notes | 2007 Notes [Member]
Debt Instrument [Line Items]
Notes principal amount							$ 370,000,000	$ 500,000,000	$ 1,725,000,000																					$ 450,000,000
Interest rate									2.00%
Convertible Notes | Two Thousand Thirteen Original Notes [Member]
Debt Instrument [Line Items]
Interest rate										2.00%												2.00%
Exceeds percentage of accreted principle amount																						120.00%
Principal convertible to common stock																						$ 1,000,000
Securitization Program
Debt Instrument [Line Items]
Credit agreement interest rate																						0.00%
Interest expense																						$ 3,300,000	$ 1,000,000
Principal amount of borrowings										$ 200,000,000												$ 200,000,000
Term of accounts receivable securitization program																						1 year
Accounts receivable from securitization										200,000,000												$ 200,000,000
Variable rate basis																						0.007
Securitization Program | Maximum
Debt Instrument [Line Items]
Accounts receivable from securitization										200,000,000												$ 200,000,000				$ 200,000,000
Two Thousand And Twelve Notes [Member]
Debt Instrument [Line Items]
Notes principal amount										17,900,000												17,900,000
Debt extinguishment loss																						(900,000)
Repayments of convertible debt										23,100,000
Conversion price (in dollars per share)											$ 31.175
Two Thousand Ten Original Notes [Member] | Convertible Notes
Debt Instrument [Line Items]
Notes principal amount										$ 46,300,000			300,000,000									$ 46,300,000	300,000,000
Debt extinguishment loss													(800,000)			$ (15,500,000)
Interest rate										2.00%												2.00%
Repayments of convertible debt													79,200,000			$ 543,700,000
Exceeds percentage of accreted principle amount																						120.00%
Conversion price of notes (in dollars per share)																						$ 23.03
Exceeds percentage of conversion price																						130.00%
Number of trading days description																						during the five business day period after any five consecutive trading day period
Percentage to compare note price to product of common stock and conversion ratio																						98.00%
Principal convertible to common stock																						$ 1,000
Principle convertible debt put during period													$ 1,300,000
Two Thousand Ten Original Notes [Member] | Convertible Notes | Minimum
Debt Instrument [Line Items]
Number of trading days																						20 days
Two Thousand Ten Original Notes [Member] | Convertible Notes | Maximum
Debt Instrument [Line Items]
Number of trading days																						30 days
Two Thousand Ten Original Notes [Member] | Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Repayments of convertible debt														$ 140,100,000
Conversion price of notes (in dollars per share)														$ 0
Two Thousand And Twelve Notes [Member] | Convertible Notes
Debt Instrument [Line Items]
Conversion price of notes (in dollars per share)																						$ 31.175
Two Thousand And Twelve Notes [Member] | Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Notes principal amount														$ 136,600,000
Debt extinguishment loss																						$ (700,000)
Repayments of convertible debt														$ 171,300,000
Conversion price of notes (in dollars per share)														$ 0
Year Two Thousand Thirteen [Member] | Convertible Notes
Debt Instrument [Line Items]
Conversion price of notes (in dollars per share)																						$ 38.59
Securitization Program
Debt Instrument [Line Items]
Credit agreement interest rate																						1.235%
Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Interest expense																						$ 41,000,000	50,000,000	70,700,000
Non-cash interest expense amortization of debt discount and deferred financing costs																						34,300,000	$ 40,000,000	$ 52,500,000
Debt extinguishment loss														$ (4,500,000)								$ (5,300,000)
Interest rate										2.00%			2.00%									2.00%	2.00%
Convertible Notes Payable [Member] | 2012 and 2013 Notes [Member]
Debt Instrument [Line Items]
Deferred taxes, reacquisition of equity component																						$ 31,100,000
Adjustments to APIC, equity component of convertible debt																						58,600,000
Convertible Notes Payable [Member] | Two Thousand Ten Original Notes [Member]
Debt Instrument [Line Items]
Debt extinguishment loss																						(4,600,000)
Convertible Notes Payable [Member] | 2010 and 2012 Notes [Member]
Debt Instrument [Line Items]
Deferred taxes, reacquisition of equity component																						28,200,000
Adjustments to APIC, equity component of convertible debt																						122,600,000
Term Loan
Debt Instrument [Line Items]
Long-term debt obligations										$ 1,190,500,000			$ 1,308,200,000									1,190,500,000	$ 1,308,200,000
Term Loan | Credit Agreement
Debt Instrument [Line Items]
Amount of credit outstanding										1,500,000,000												$ 1,500,000,000
Debt instrument, maturity date																						May 29, 2020
Term Loan | Credit Agreement | Minimum
Debt Instrument [Line Items]
Scheduled principal payments per quarter																						$ 18,750,000
Term Loan | Credit Agreement | Maximum
Debt Instrument [Line Items]
Scheduled principal payments per quarter																						37,500,000
Revolver | Credit Agreement
Debt Instrument [Line Items]
Amount of credit outstanding										$ 1,000,000,000												$ 1,000,000,000
Debt instrument, maturity date																						May 29, 2020
Amount borrowed under revolver					$ 175,000,000
Term Loan A [Member] | Credit Agreement
Debt Instrument [Line Items]
Amount of credit outstanding					1,000,000,000
Debt instrument, maturity date																					Aug. 1, 2017
Revolving Credit Facility | Credit Agreement
Debt Instrument [Line Items]
Amount of credit outstanding					300,000,000
Debt instrument, maturity date																					Aug. 1, 2017
Term Loan B [Member] | Credit Agreement
Debt Instrument [Line Items]
Amount of credit outstanding					$ 1,500,000,000
Debt instrument, maturity date																					Aug. 1, 2019
Debt extinguishment loss															$ (6,700,000)
Prepaid principal amount						$ 300,000,000
2007 Notes [Member] | Convertible Notes
Debt Instrument [Line Items]
Debt instrument, maturity period									2,037
November Eighteen Two Thousand Ten Original Notes [Member] | Convertible Notes
Debt Instrument [Line Items]
Notes principal amount																														$ 450,000,000
Interest rate																														2.00%
Debt instrument, maturity period																		2,037
November Eighteen Two Thousand Ten Original Notes [Member] | Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Notes principal amount														$ 90,000,000
February Twenty Nine Two Thousand Twelve Original Notes [Member]
Debt Instrument [Line Items]
Convertible notes, triggering events										$ 0												$ 0
February Twenty Nine Two Thousand Twelve Original Notes [Member] | Convertible Notes
Debt Instrument [Line Items]
Notes principal amount								$ 500,000,000
Interest rate								2.00%
Debt instrument, maturity period								2,042
Two Thousand Twelve Original Notes [Member] | Convertible Notes
Debt Instrument [Line Items]
Interest rate										2.00%												2.00%
Annual yield to maturity																						2.00%
Exceeds percentage of accreted principle amount																						120.00%
Exceeds percentage of conversion price																						130.00%
Number of trading days description																						During the five business day period after any five consecutive trading day period
Percentage to compare note price to product of common stock and conversion ratio																						98.00%
Principal convertible to common stock																						$ 1,000,000
Two Thousand Twelve Original Notes [Member] | Convertible Notes | Minimum
Debt Instrument [Line Items]
Number of trading days																						20 days
Two Thousand Twelve Original Notes [Member] | Convertible Notes | Maximum
Debt Instrument [Line Items]
Number of trading days																						30 days
Due December Two Zero One Seven [Member] | Convertible Notes | Two Thousand Thirteen Original Notes [Member]
Debt Instrument [Line Items]
Annual yield to maturity																						4.00%
Thereafter [Member] | Convertible Notes | Two Thousand Thirteen Original Notes [Member]
Debt Instrument [Line Items]
Annual yield to maturity																						2.00%
Two Thousand Thirteen Original Notes [Member] | Convertible Notes
Debt Instrument [Line Items]
Exceeds percentage of conversion price																						130.00%
Number of trading days description																						During the five business day period after any five consecutive trading day period
Percentage to compare note price to product of common stock and conversion ratio																						98.00%
Convertible notes, triggering events										$ 0												$ 0
Two Thousand Thirteen Original Notes [Member] | Convertible Notes | Minimum
Debt Instrument [Line Items]
Number of trading days																						20 days
Two Thousand Thirteen Original Notes [Member] | Convertible Notes | Maximum
Debt Instrument [Line Items]
Number of trading days																						30 days
February Fourteen Two Thousand And Thirteen Original Notes [Member] | Convertible Notes
Debt Instrument [Line Items]
Notes principal amount							$ 370,000,000
Interest rate							2.00%
Debt instrument, maturity period							2,043
Convertible Debt [Member] | 2010 Notes [Member]
Debt Instrument [Line Items]
Redemption price, percentage			100.00%	100.00%
Senior Notes
Debt Instrument [Line Items]
Aggregate redemption price																											1,030,000,000
Premium payment																											$ 31,250,000
Subsequent Event | Term Loan | Credit Agreement
Debt Instrument [Line Items]
Amount of credit outstanding																									$ 1,500,000,000
Subsequent Event | Senior Notes | 2025 Notes
Debt Instrument [Line Items]
Notes principal amount		$ 350,000,000
Interest rate		4.375%
Offering price, percentage of principal amount		100.00%
Maximum percentage of redemption of senior notes		35.00%
Percentage of redemption price, second period		104.375%
Percentage of redemption price, third period		102.188%
Percentage of redemption price, fourth period		101.094%
Percentage of redemption price, fifth period		100.00%
Percentage price of principal amount for repurchase of senior note		101.00%
On or After December 15, 2017 [Member] | Convertible Notes
Debt Instrument [Line Items]
Debt instrument, maturity date range, start				Dec. 15, 2017
Redemption price as percentage of principle amount plus accrued and unpaid interest																						100.00%
December 15, 2017 [Member] | Subsequent Event | Convertible Debt [Member] | 2013 Notes
Debt Instrument [Line Items]
Redemption price, percentage	100.00%

Borrowings and Credit Arrange67

Borrowings and Credit Arrangements - Convertible Notes and Related Equity Components (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Jul. 01, 2017
Schedule Of Borrowings [Line Items]
Notes principal amount			$ 100
Two Thousand And Ten Notes [Member]
Schedule Of Borrowings [Line Items]
Notes principal amount	$ 0	$ 12.3
Unamortized discount and issuance costs	0	(0.1)
Net carrying amount	0	12.2
Equity component, net of taxes	0	1.6
Two Thousand And Twelve Notes [Member]
Schedule Of Borrowings [Line Items]
Notes principal amount	245.4	363.4
Unamortized discount and issuance costs	(1.9)	(9.5)
Net carrying amount	243.5	353.9
Equity component, net of taxes	24.1	35.8
Two Thousand And Thirteen Notes [Member]
Schedule Of Borrowings [Line Items]
Notes principal amount	202	370
Unamortized discount and issuance costs	(1.8)	(17.5)
Net carrying amount	241	409.6
Equity component, net of taxes	71.8	131.5
Principal accretion	$ 40.8	$ 57.1

Borrowings and Credit Arrange68

Borrowings and Credit Arrangements - Interest Expense under Convertible Notes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Debt Conversion [Line Items]
Non-cash interest expense	$ 49.4	$ 52.1	$ 63.8
Convertible Notes Payable [Member]
Debt Conversion [Line Items]
Amortization of debt discount	17.9	22.3	34.9
Amortization of deferred financing costs	0.8	1.1	1.7
Principal accretion	15.6	16.6	15.9
Non-cash interest expense	34.3	40	52.5
2.00% accrued interest	6.7	10	18.2
Interest expense, net	$ 41	$ 50	$ 70.7
Percentage of accrued interest on Convertible Notes	2.00%	2.00%

Borrowings and Credit Arrange69

Borrowings and Credit Arrangements - Subsequent Events (Details) - USD ($) $ in Thousands	Oct. 10, 2017	Oct. 03, 2017	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015	Oct. 31, 2017	Jul. 01, 2017
Debt Instrument [Line Items]
Proceeds used from credit agreement			$ 345,000	$ 50,000	$ 358,000
Notes principal amount							$ 100,000
Subsequent Event | Amended and Restated Credit Agreement
Debt Instrument [Line Items]
Proceeds used from credit agreement		$ 1,800,000
Subsequent Event | Revolving Credit Facility | Amended Revolver
Debt Instrument [Line Items]
Line of credit		1,500,000
Borrowings under the Amended Revolver		$ 345,000
Subsequent Event | Revolving Credit Facility | Amended Revolver | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate		1.50%
Subsequent Event | Secured Term Loan | Amended Term Loan
Debt Instrument [Line Items]
Line of credit						$ 1,500,000
Subsequent Event | Secured Term Loan | Amended Term Loan | Minimum
Debt Instrument [Line Items]
Scheduled principal payments per quarter		$ 9,375
Subsequent Event | Secured Term Loan | Amended Term Loan | Maximum
Debt Instrument [Line Items]
Scheduled principal payments per quarter		$ 37,500
Subsequent Event | Secured Term Loan | Amended Term Loan | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate		1.50%
Subsequent Event | Senior Notes | 2025 Notes
Debt Instrument [Line Items]
Notes principal amount	$ 350,000
Interest rate	4.375%
Offering price, percentage of principal amount	100.00%
Maximum percentage of redemption of senior notes	35.00%
Percentage of redemption price, second period	104.375%
Percentage of redemption price, third period	102.188%
Percentage of redemption price, fourth period	101.094%
Percentage of redemption price, fifth period	100.00%
Percentage price of principal amount for repurchase of senior note	101.00%
Subsequent Event | Senior Notes | 2025 Indenture
Debt Instrument [Line Items]
Interest rate	4.375%

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($)	Sep. 30, 2017	Sep. 24, 2016
Assets:
Assets measured at fair value on a recurring basis	$ 5,300,000	$ 2,600,000
Liabilities:
Liabilities measured at fair value on a recurring basis	47,200,000	38,300,000
Quoted Prices in Active Market for Identical Assets (Level 1)
Assets:
Assets measured at fair value on a recurring basis	100,000	1,000,000
Liabilities:
Liabilities measured at fair value on a recurring basis	43,200,000	37,000,000
Significant Other Observable Inputs (Level 2)
Assets:
Assets measured at fair value on a recurring basis	5,200,000	1,600,000
Liabilities:
Liabilities measured at fair value on a recurring basis	4,000,000	1,300,000
Significant Unobservable Inputs (Level 3)
Assets:
Assets measured at fair value on a recurring basis	0	0
Liabilities:
Liabilities measured at fair value on a recurring basis	0	0
Equity securities
Assets:
Assets measured at fair value on a recurring basis	100,000	1,000,000
Equity securities | Quoted Prices in Active Market for Identical Assets (Level 1)
Assets:
Assets measured at fair value on a recurring basis	100,000	1,000,000
Equity securities | Significant Other Observable Inputs (Level 2)
Assets:
Assets measured at fair value on a recurring basis	0	0
Equity securities | Significant Unobservable Inputs (Level 3)
Assets:
Assets measured at fair value on a recurring basis	0	0
Interest rate caps - derivative
Assets:
Assets measured at fair value on a recurring basis		1,400,000
Interest rate caps - derivative	4,800,000	1,400,000
Interest rate caps - derivative | Quoted Prices in Active Market for Identical Assets (Level 1)
Assets:
Assets measured at fair value on a recurring basis		0
Interest rate caps - derivative	0
Interest rate caps - derivative | Significant Other Observable Inputs (Level 2)
Assets:
Assets measured at fair value on a recurring basis		1,400,000
Interest rate caps - derivative	4,800,000
Interest rate caps - derivative | Significant Unobservable Inputs (Level 3)
Assets:
Assets measured at fair value on a recurring basis		0
Interest rate caps - derivative	0
Deferred compensation liabilities
Liabilities:
Liabilities measured at fair value on a recurring basis	43,200,000	37,000,000
Deferred compensation liabilities | Quoted Prices in Active Market for Identical Assets (Level 1)
Liabilities:
Liabilities measured at fair value on a recurring basis	43,200,000	37,000,000
Deferred compensation liabilities | Significant Other Observable Inputs (Level 2)
Liabilities:
Liabilities measured at fair value on a recurring basis	0	0
Deferred compensation liabilities | Significant Unobservable Inputs (Level 3)
Liabilities:
Liabilities measured at fair value on a recurring basis	0	0
Forward foreign currency contracts
Liabilities:
Liabilities measured at fair value on a recurring basis		1,300,000
Forward foreign currency contracts | Quoted Prices in Active Market for Identical Assets (Level 1)
Liabilities:
Liabilities measured at fair value on a recurring basis		0
Forward foreign currency contracts | Significant Other Observable Inputs (Level 2)
Liabilities:
Liabilities measured at fair value on a recurring basis		1,300,000
Forward foreign currency contracts | Significant Unobservable Inputs (Level 3)
Liabilities:
Liabilities measured at fair value on a recurring basis		0
Forward foreign currency contracts | Assets
Assets:
Interest rate caps - derivative		200,000
Forward foreign currency contracts	400,000
Forward foreign currency contracts | Assets | Quoted Prices in Active Market for Identical Assets (Level 1)
Assets:
Interest rate caps - derivative		0
Forward foreign currency contracts	0
Forward foreign currency contracts | Assets | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate caps - derivative		200,000
Forward foreign currency contracts	400,000
Forward foreign currency contracts | Assets | Significant Unobservable Inputs (Level 3)
Assets:
Interest rate caps - derivative		$ 0
Forward foreign currency contracts	0
Forward foreign currency contracts | Liability
Liabilities:
Liabilities measured at fair value on a recurring basis	4,000,000
Forward foreign currency contracts | Liability | Quoted Prices in Active Market for Identical Assets (Level 1)
Liabilities:
Liabilities measured at fair value on a recurring basis	0
Forward foreign currency contracts | Liability | Significant Other Observable Inputs (Level 2)
Liabilities:
Liabilities measured at fair value on a recurring basis	4,000,000
Forward foreign currency contracts | Liability | Significant Unobservable Inputs (Level 3)
Liabilities:
Liabilities measured at fair value on a recurring basis	$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	Sep. 30, 2017	Sep. 24, 2016	Aug. 01, 2012
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Investments, fair value	$ 5,300,000	$ 2,600,000
Borrowed principal under credit agreement	1,000,000,000
Credit Agreement
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Borrowed principal under credit agreement	1,670,000,000		$ 2,500,000,000
Securitization Program
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Borrowed principal under credit agreement	200,000,000
Senior Notes
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fair value of debt instrument	1,050,000,000	1,060,000,000
Significant Unobservable Inputs (Level 3)
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Investments, fair value	$ 0	$ 0

Fair Value Measurements - Estim

Fair Value Measurements - Estimated Fair Values of Convertible Notes (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Estimated Fair Value Of Financial Instruments [Line Items]
Estimated fair values of debt instruments	$ 541.7	$ 960.9
2010 Notes
Estimated Fair Value Of Financial Instruments [Line Items]
Estimated fair values of debt instruments	0	20.2
2012 Notes
Estimated Fair Value Of Financial Instruments [Line Items]
Estimated fair values of debt instruments	297.3	481.9
2013 Notes
Estimated Fair Value Of Financial Instruments [Line Items]
Estimated fair values of debt instruments	$ 244.4	$ 458.8

Income Taxes - Income (Loss) Be

Income Taxes - Income (Loss) Before Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Income Tax Disclosure [Abstract]
Domestic	$ 1,105.8	$ 310.7	$ 158.3
Foreign	124.7	104.6	18.9
Income before income taxes	$ 1,230.5	$ 415.3	$ 177.2

Income Taxes - Provision for In

Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Federal:
Current	$ 701.1	$ 209	$ 185.2
Deferred	(276.9)	(122.7)	(137)
Federal, Total	424.2	86.3	48.2
State:
Current	53.1	16.6	3.5
Deferred	(15.9)	(22.7)	(11)
State, Total	37.2	(6.1)	(7.5)
Foreign:
Current	13.9	14.7	5.7
Deferred	(0.3)	(10.4)	(0.8)
Foreign, Total	13.6	4.3	4.9
Provision for income taxes	$ 475	$ 84.5	$ 45.6

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax (Benefit) at U.S. Federal Statutory Rate to Company's Effective Tax Rate (Detail)	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Income Tax Disclosure [Abstract]
Income tax provision at federal statutory rate	35.00%	35.00%	35.00%
Increase (decrease) in tax resulting from:
Domestic production activities deduction	(1.70%)	(5.00%)	(10.10%)
State income taxes, net of federal benefit	2.30%	2.00%	1.20%
Non-deductible goodwill	9.20%	0.00%	0.00%
Tax credits	(0.80%)	(3.20%)	(3.80%)
Unrecognized tax benefits	(1.40%)	2.40%	(1.80%)
Cumulative translation adjustment write-off	0.00%	0.00%	1.90%
Compensation	(0.50%)	0.10%	1.90%
Foreign rate differential	(2.60%)	(6.10%)	(1.60%)
Change in deferred tax rate	0.20%	(1.80%)	0.00%
Change in valuation allowance	(1.50%)	(3.40%)	1.00%
Other	0.40%	0.30%	2.10%
Effective income tax rate	38.60%	20.30%	25.80%

Income Taxes - Significant Comp

Income Taxes - Significant Components of Company's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Deferred tax assets
Net operating loss carryforwards	$ 50.1	$ 40
Capital losses	7.1	19.1
Non-deductible accruals	50.6	21.1
Non-deductible reserves	30	31.1
Stock-based compensation	39.3	34.8
Research and other credits	13.6	10.7
Nonqualified deferred compensation plan	16.4	14.1
Other temporary differences	16.5	9.2
Deferred tax assets, gross	223.6	180.1
Less: valuation allowance	(28.2)	(46.2)
Deferred tax assets, net	195.4	133.9
Deferred tax liabilities
Depreciation and amortization	(1,071.5)	(1,030.8)
Debt discounts and deferrals	(88.4)	(76.4)
Deferred tax liabilities, net	(1,159.9)	(1,107.2)
Net deferred tax liabilities	$ (964.5)	$ (973.3)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016
Income Taxes [Line Items]
Decrease in valuation allowance	$ 18,000,000
Federal net operating loss expected to be expired unutilized	4,500,000
State net operating loss expected to be expired unutilized	117,900,000
Foreign net operating loss expected to be expired unutilized	45,400,000
Gross unrecognized tax benefits, excluding interest	90,300,000	$ 163,600,000
Unrecognized tax benefit that would impact effective tax rate	70,300,000	76,900,000
Unrecognized tax benefits, period decrease	73,300,000
Interest accrued on unrecognized tax benefits	5,300,000	$ 13,100,000
Income tax penalties accrued	0
Payments for other taxes	1,700,000
Recognized tax benefit due to reversal of unrecognized tax benefit	10,900,000
Unremitted foreign earnings	309,500,000
Non-income tax loss	35,600,000
General and Administrative Expense [Member]
Income Taxes [Line Items]
Income tax refund	(12,400,000)
Convertible Debt Securities [Member]
Income Taxes [Line Items]
Unrecognized tax benefits, period decrease	(64,000,000)
Settlement with Taxing Authority [Member]
Income Taxes [Line Items]
Unrecognized tax benefits, period decrease	(9,300,000)
Net Operating Losses Carryforwards [Member]
Income Taxes [Line Items]
Amount with unlimited carry forward periods	33,700,000
Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Amount with unlimited carry forward periods	2,200,000
Maximum
Income Taxes [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	2,000,000
Domestic Tax Authority [Member]
Income Taxes [Line Items]
Net operating losses	64,300,000
Credit carry forwards	5,200,000
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Net operating losses	91,400,000
Credit carry forwards	10,300,000
Foreign Tax Authority [Member]
Income Taxes [Line Items]
Net operating losses	36,500,000
Credit carry forwards	$ 5,800,000

Income Taxes - Activity of Comp

Income Taxes - Activity of Company's Unrecognized Income Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016
Income Tax Disclosure [Abstract]
Balance at beginning of fiscal year	$ 163.6	$ 154.7
Tax positions related to current year:
Additions	21.8	23.9
Reductions	0	0
Tax positions related to prior years:
Additions related to change in estimate	1.1	1.1
Reductions	(77.3)	(6.9)
Payments	(1.6)	(6)
Lapses in statutes of limitations	(19.9)	(3.2)
Acquired tax positions:
Additions related to reserves acquired from acquisitions	2.6	0
Balance as of the end of the fiscal year	$ 90.3	$ 163.6

Stockholders' Equity and Stoc79

Stockholders' Equity and Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, shares in Millions, $ in Millions	Jun. 21, 2016	Dec. 31, 2013tranche$ / sharesshares	Mar. 31, 2012shares	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 24, 2016USD ($)$ / sharesshares	Sep. 26, 2015USD ($)$ / sharesshares	Nov. 11, 2013USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market stock units granted during the period | shares		0.1
Share Based Compensation Arrangement By Share Based Payment Award Number Of Tranches | tranche		3
Percentage Of Award Vested Upon Meeting Defined Market Based Criteria		33.33%
Share Based Compensation Arrangement By Share Based Payment Award Trading Period Considered For Determination Of Average Price		30 days
Valuation of MSUs using Monte Carlo simulation model | $ / shares		$ 18.65
Share Based Compensation Arrangement Restricted Stock Units Liability Award | shares		0.2
Common Stock Purchased By Employee | shares		0.2
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share-based Liabilities Paid				$ 7.8
Stock-based compensation, period of vest term granted to employees, years				3 years
Share-based Compensation Arrangement by Share-based Payment Award, Cliff-Vesting Period from Grant Date				3 years
Stock Modification Expense				$ 4
Tax benefit related to stock based compensation				22.6	$ 23.1	$ 17.7
Expense related to the acceleration of vesting for certain options assumed in acquisition					0.4	4.1
Intrinsic value of option exercised				$ 25.9	21.6	42
Granted | shares				1
Minimum eligible percentage to receive target number of shares of company's common stock				0.00%
Maximum eligible percentage to receive target number of shares of company's common stock				200.00%
Stock-based compensation expense				$ 68.2	65.4	59.3
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of forfeiture rates				0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of forfeiture rates				7.00%
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 12.2	10.9	12.2
Unrecognized compensation expense				$ 21
Weighted average period of unrecognized stock-based compensation, years				2 years 5 months 22 days
Stock Options [Member] | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, period of vest term granted to employees, years				4 years
Percentage of vesting for stock options granted to employees				25.00%
Stock Options [Member] | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, period of vest term granted to employees, years				5 years
Percentage of vesting for stock options granted to employees				20.00%
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shared Based Compensation Arrangement Restricted Stock Vesting Period		3 years
Stock-based compensation expense				$ 51.6	50.5	43.7
Unrecognized compensation expense				$ 54.6
Weighted average period of unrecognized stock-based compensation, years				1 year 9 months 27 days
Fair value of RSUs vested				$ 38.5	$ 28.4	$ 27.2
Restricted Stock Units [Member] | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, period of vest term granted to employees, years				3 years
Percentage of vesting for RSUs granted to employees				25.00%
Restricted Stock Units [Member] | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation, period of vest term granted to employees, years				4 years
Percentage of vesting for RSUs granted to employees				33.00%
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted | shares				0.2	0.2	0.3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value | $ / shares				$ 38.84	$ 39.72	$ 26.58
Market Based Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Cliff-Vesting Period from Grant Date				3 years
Granted | shares				0.1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value | $ / shares				$ 48.98
Minimum eligible percentage to receive target number of shares of company's common stock				0.00%
Maximum eligible percentage to receive target number of shares of company's common stock				200.00%
2008 Equity Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized | shares				31.5
Shares available for grant | shares				6.8
2012 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares that may be issued under Employee Stock Purchase Plan | shares			2.5
Percentage of common stock price for ESPP			85.00%
Stock-based compensation expense				$ 4.4	$ 4	$ 3.4
Nov 11, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized value of common shares to be repurchased							$ 250
Period available for common stock to be repurchased				3 years
Treasury Stock, Shares, Acquired | shares					7.3
Stock Repurchased During Period, Total Consideration				$ 250
Jun 21 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period available for common stock to be repurchased				5 years
Treasury Stock, Shares, Acquired | shares				0
Treasury Stock Acquired, Repurchase Authorization	500
June 21, 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Treasury Stock, Shares, Acquired | shares				5.3
Stock Repurchased During Period, Value				$ 200.1

Stockholders' Equity and Stoc80

Stockholders' Equity and Stock-Based Compensation - Stock-Based Compensation Expense in Consolidated Statement of Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 68.2	$ 65.4	$ 59.3
Cost of Sales [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	10.7	10.5	8.7
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	11.2	10.8	8.6
Selling and Marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	11.9	10.9	8.8
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	34.4	32.8	29.1
Restructuring Charges [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 0	$ 0.4	$ 4.1

Stockholders' Equity and Stoc81

Stockholders' Equity and Stock-Based Compensation - Information Pertaining to Stock Options Granted and Related Assumptions (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	1	1.1	1.3
Weighted-average exercise price	$ 38.07	$ 39.32	$ 27.68
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value	$ 12.33	$ 0	$ 0
Assumptions:
Risk-free interest rates	1.80%	1.60%	1.70%
Expected life (in years)	4 years 8 months 15 days	4 years 8 months 15 days	5 years 4 months 6 days
Expected volatility	36.60%	37.80%	38.60%
Dividend yield	$ 0	$ 0	$ 0

Stockholders' Equity and Stoc82

Stockholders' Equity and Stock-Based Compensation - Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	1
Number of Shares (in millions)
Options outstanding at September 24, 2016	6.1
Granted	1	1.1	1.3
Canceled/ forfeited	(0.2)
Exercised	(1.4)
Options outstanding at September 30, 2017	5.5	6.1
Options exercisable at September 30, 2017	2.6
Options vested and expected to vest at September 30, 2017 (1)	5.4
Weighted- Average Exercise Price
Options outstanding at September 24, 2016	$ 25.37
Granted	38.07	$ 39.32	$ 27.68
Canceled/ forfeited	30.59
Exercised	23.25
Options outstanding at September 24, 2016	28.15	$ 25.37
Options exercisable at September 30, 2017	23.31
Options vested and expected to vest at September 30, 2017 (1)	$ 28.09
Weighted- Average Remaining Contractual Life (in Years)
Options outstanding at September 24, 2016	5 years 5 months 11 days	4 years 10 months 12 days
Options exercisable at September 30, 2017	3 years 7 months 12 days
Options vested and expected to vest at September 30, 2017 (1)	5 years 5 months 29 days
Options outstanding at September 30, 2017	5 years 5 months 11 days	4 years 10 months 12 days
Aggregate Intrinsic Value (in millions)
Options outstanding at September 24, 2016	$ 80.1
Exercised	25.9	$ 21.6	$ 42
Options outstanding at September 30, 2017	50.3	$ 80.1
Options exercisable at September 30, 2017	34.8
Options vested and expected to vest at September 30, 2017 (1)	$ 50
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	0.2	0.2	0.3
Market Based Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	0.1

Stockholders' Equity and Stoc83

Stockholders' Equity and Stock-Based Compensation - Restricted Stock Unit Activity (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Tax benefit related to stock based compensation	$ 22.6	$ 23.1	$ 17.7
Number of Shares (in millions)
Non-vested at September 24, 2016	2.8
Granted	1
Vested	(1.2)
Forfeited	(0.3)
Non-vested at September 30, 2017	2.3	2.8
Weighted-Average Grant-Date Fair Value
Non-vested at September 24, 2016	$ 29.40
Granted	38.03
Vested	27.43
Forfeited	32.21
Non-vested at September 30, 2017	$ 34.06	$ 29.40

Stockholders' Equity and Stoc84

Stockholders' Equity and Stock-Based Compensation - Assumptions to Value Stock Options (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Assumptions:
Risk-free interest rates	1.80%	1.60%	1.70%
Expected life (in years)	4 years 8 months 15 days	4 years 8 months 15 days	5 years 4 months 6 days
Expected volatility	36.60%	37.80%	38.60%
Dividend yield	$ 0	$ 0	$ 0
Employee stock purchase plan [Member]
Assumptions:
Risk-free interest rates	0.72%	0.34%	0.10%
Expected life (in years)	6 months	6 months	6 months
Expected volatility	24.90%	27.20%	27.40%
Dividend yield	$ 0	$ 0	$ 0

Profit Sharing 401(k) Plan - Ad

Profit Sharing 401(k) Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Contributions made by company	$ 20.2	$ 16.2	$ 14.4

Deferred Compensation Plan - Ad

Deferred Compensation Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Gen-Probe Incorporated [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Compensation expense for the DCP discretionary contributions	$ 43.2	$ 37
Nonqualified Deferred Compensation Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Maximum employee contributions from base salary, percentage	75.00%
Maximum employee contributions from annual bonus, percentage	100.00%
Employee contributions vested, percentage	100.00%
Percent vested annually	33.33%
Contributions, vesting period, years	3 years
Compensation expense for the DCP discretionary contributions	$ 3.4	3.1	$ 1.8
Investment in group life insurance contracts	$ 41	$ 36
Nonqualified Deferred Compensation Plan [Member] | One Third Annually [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Contributions, vesting period, years	3 years

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)Leaseterm	Sep. 24, 2016USD ($)	Sep. 26, 2015USD ($)
Contingent Consideration Earn-Out Payments [Line Items]
Accrued expenses	$ 375.3	$ 287.6
Operating lease expiration year	2,035
Rent expense net of sublease income	$ 19.3	17.9	$ 19.2
Rent expense on sublease rentals	$ 2.3	$ 2.4	$ 2
Finance Leases [Member]
Contingent Consideration Earn-Out Payments [Line Items]
Number of finance leases | Lease	2
Fair value	$ 28.3
Finance lease extension executed	1
Finance lease expiration year	2,024
Accrued expenses	$ 3.2
Accrued lease obligation-long-term	$ 34.1
Optional lease extension period	10 years
Number of optional lease extensions | term	2
Lease extension period	5 years
Finance Lease 2 [Member]
Contingent Consideration Earn-Out Payments [Line Items]
Optional lease extension period	8 years
Number of optional lease extensions | term	1
Lease extension period	5 years
Finance Leases [Member] | Leasehold Improvements [Member]
Contingent Consideration Earn-Out Payments [Line Items]
Property, plant and equipment, estimated useful life	35 years

Commitments and Contingencies88

Commitments and Contingencies - Future Minimum Lease Payments, Including Principal and Interest (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Other Commitments [Line Items]
Fiscal 2,018	$ 2.9
Fiscal 2,019	1.2
Fiscal 2,020	1.2
Fiscal 2,021	1.2
Fiscal 2,022	1.2
Thereafter	1.7
Total minimum payments	9.4
Less-amount representing interest	(3)
Present value of obligations under capital lease	6.4
Current portion of capital lease obligations	1.6	$ 0
Capital lease obligations, net of current portion	22.7	$ 0
Cynosure [Member]
Other Commitments [Line Items]
Fiscal 2,018	2.8
Fiscal 2,019	2.8
Fiscal 2,020	2.8
Fiscal 2,021	2.9
Fiscal 2,022	3
Thereafter	17.3
Total minimum payments	31.6
Less-amount representing interest	(7.3)
Present value of obligations under capital lease	$ 24.3

Commitments and Contingencies89

Commitments and Contingencies - Summary of Purchase Commitments (Details) $ in Millions	Sep. 30, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
Fiscal 2,018	$ 56.4
Fiscal 2,019	4.7
Fiscal 2,020	1.1
Fiscal 2,021	1.1
Fiscal 2,022	1.1
Total	$ 64.4

Commitments and Contingencies90

Commitments and Contingencies - Future Minimum Lease Payments Under All Operating Leases (Details) $ in Millions	Sep. 30, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
Fiscal 2,018	$ 20.9
Fiscal 2,019	18
Fiscal 2,020	15.2
Fiscal 2,021	12.5
Fiscal 2,022	11.4
Thereafter	27
Total	$ 105

Commitments and Contingencies91

Commitments and Contingencies - Future Minimum Annual Rental Income Payments Under Sublease Agreements (Details) $ in Millions	Sep. 30, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
Fiscal 2,018	$ 2.3
Fiscal 2,019	2.3
Fiscal 2,020	1.5
Fiscal 2,021	0.4
Fiscal 2,022	0.4
Thereafter	0.7
Total	$ 7.6

Litigation and Other Matters -

Litigation and Other Matters - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions	Oct. 07, 2016	Apr. 01, 2017	Dec. 31, 2016	Mar. 22, 2017	Sep. 04, 2012
Loss Contingencies [Line Items]
Assessed damages					$ 4,000,000
Plaintiff statutory damages offer, individual basis	$ 25
Litigation settlement amount		$ 8,500,000
Litigation settlement expense			$ 9,200,000
Cynosure [Member]
Loss Contingencies [Line Items]
Outstanding noncontrolling shares (in shares)				1.2
Noncontrolling interest				$ 79,200,000
Purchase price (in dollars per share)				$ 66

Disposition - Additional Inform

Disposition - Additional Information (Details) - USD ($) $ in Millions	Dec. 14, 2016	Apr. 01, 2017	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of businesses			$ 1,865	$ 0	$ 0
Blood Screening Business | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales price	$ 1,850
Proceeds from divestiture of businesses		$ 1,865
Gain on disposal		$ 899.7
Tax obligation			649.5
Proceeds allocated to manufacture of inventory			13.1
Disposal group, revenue			$ 44
Minimum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement term		2 years
Minimum | Blood Screening Business | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement term	2 years
Maximum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement term		3 years
Maximum | Blood Screening Business | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement term	3 years

Disposition - Income from Opera

Disposition - Income from Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016
Blood Screening Business | Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income from operations	$ 45.8	$ 99.1

Disposition - Prior Collaborati

Disposition - Prior Collaboration Agreement (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2009	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreements revenue		$ 96.5	$ 235.4	$ 253.1
Grifols [Member] | Blood screening [Member] | Collaboration Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Manufacturing costs entitled to recover	50.00%
Share of Revenue from Any Assay	50.00%

Business Segments and Geograp96

Business Segments and Geographic Information - Additional Information (Detail)	3 Months Ended								12 Months Ended
	Sep. 30, 2017USD ($)	Jul. 01, 2017USD ($)	Apr. 01, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 24, 2016USD ($)	Jun. 25, 2016USD ($)	Mar. 26, 2016USD ($)	Dec. 26, 2015USD ($)	Sep. 30, 2017USD ($)Segment	Sep. 24, 2016USD ($)	Sep. 26, 2015USD ($)
Segment Reporting Disclosure [Line Items]
Number of reportable segments | Segment									5
Revenues	$ 802,900,000	$ 806,100,000	$ 715,400,000	$ 734,400,000	$ 726,800,000	$ 717,400,000	$ 693,300,000	$ 695,200,000	$ 3,058,800,000	$ 2,832,700,000	$ 2,705,000,000
Intersegment
Segment Reporting Disclosure [Line Items]
Revenues									$ 0	$ 0	$ 0

Business Segments and Geograp97

Business Segments and Geographic Information - Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 24, 2016	Jun. 25, 2016	Mar. 26, 2016	Dec. 26, 2015	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Segment Reporting Information [Line Items]
Total revenue	$ 802.9	$ 806.1	$ 715.4	$ 734.4	$ 726.8	$ 717.4	$ 693.3	$ 695.2	$ 3,058.8	$ 2,832.7	$ 2,705
Operating income									1,370.2	548.6	455.1
Depreciation and amortization									449.2	465.4	491.4
Capital expenditures									107.6	94.5	89.4
Identifiable assets	7,979.6				7,317				7,979.6	7,317	7,642.5
Corporate
Segment Reporting Information [Line Items]
Capital expenditures									21	12.3	11.1
Identifiable assets	1,262.7				1,134.4				1,262.7	1,134.4	1,087.9
Diagnostics
Segment Reporting Information [Line Items]
Total revenue									1,197.1	1,236.9	1,211.8
Operating income									1,054.2	126	109.5
Depreciation and amortization									278.9	341.8	358.7
Capital expenditures									50.9	53.5	55.6
Identifiable assets	2,621.6				3,771.9				2,621.6	3,771.9	4,055.8
Breast Health
Segment Reporting Information [Line Items]
Total revenue									1,138.3	1,112.8	1,063.4
Operating income									373.4	350.5	296.3
Depreciation and amortization									19.7	22.6	28.6
Capital expenditures									12	10.6	12.8
Identifiable assets	824				809.1				824	809.1	815.4
Medical Aesthetics
Segment Reporting Information [Line Items]
Total revenue									207.5	0	0
Operating income									(115.9)	0	0
Depreciation and amortization									54.2	0	0
Capital expenditures									7.3	0	0
Identifiable assets	1,751.2				0				1,751.2	0	0
GYN Surgical
Segment Reporting Information [Line Items]
Total revenue									427.1	393.1	335.8
Operating income									65	69.1	38.6
Depreciation and amortization									95.7	99.9	102.7
Capital expenditures									15.2	17.7	9.5
Identifiable assets	1,494.6				1,570.7				1,494.6	1,570.7	1,658.1
Skeletal Health
Segment Reporting Information [Line Items]
Total revenue									88.8	89.9	94
Operating income									(6.5)	3	10.7
Depreciation and amortization									0.7	1.1	1.4
Capital expenditures									1.2	0.4	0.4
Identifiable assets	$ 25.5				$ 30.9				$ 25.5	$ 30.9	$ 25.3

Business Segments and Geograp98

Business Segments and Geographic Information - Revenues by Geography (Detail)	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Schedule Of Geographical Segments [Line Items]
Revenues	100.00%	100.00%	100.00%
United States
Schedule Of Geographical Segments [Line Items]
Revenues	77.60%	78.90%	76.00%
Europe
Schedule Of Geographical Segments [Line Items]
Revenues	10.00%	10.20%	11.80%
Asia-Pacific
Schedule Of Geographical Segments [Line Items]
Revenues	8.10%	7.60%	8.50%
Rest of world
Schedule Of Geographical Segments [Line Items]
Revenues	4.30%	3.30%	3.70%

Business Segments and Geograp99

Business Segments and Geographic Information - Schedule of Geographically Located Property and Equipment, Net (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Geographic Information For Property Plant And Equipment [Line Items]
Property, plant and equipment, net	$ 491.2	$ 460.2	$ 457.1
United States
Geographic Information For Property Plant And Equipment [Line Items]
Property, plant and equipment, net	386.5	370.7	369.1
Costa Rica
Geographic Information For Property Plant And Equipment [Line Items]
Property, plant and equipment, net	30.1	28.1	27.7
Europe
Geographic Information For Property Plant And Equipment [Line Items]
Property, plant and equipment, net	57.1	49.2	50.8
Rest of world
Geographic Information For Property Plant And Equipment [Line Items]
Property, plant and equipment, net	$ 17.5	$ 12.2	$ 9.5

Accrued Expenses and Other L100

Accrued Expenses and Other Long-Term Liabilities - Schedule of Accrued Expenses (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Accrued Expenses
Compensation and employee benefits	$ 176.7	$ 176.4
Income and other taxes	66.9	38.4
Other	131.7	72.8
Total	$ 375.3	$ 287.6

Accrued Expenses and Other L101

Accrued Expenses and Other Long-Term Liabilities - Schedule of Other Long-Term Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Other Long-Term Liabilities
Reserve for income tax uncertainties	$ 88.3	$ 167.6
Accrued lease obligation—long-term	34.1	34.8
Pension liabilities	10	11.2
Other	7.8	10.9
Total	$ 140.2	$ 224.5

Pension and Other Employee B102

Pension and Other Employee Benefits - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 24, 2016
Other Liabilities Disclosure [Abstract]
Defined benefit pension plan, liabilities	$ (9.9)	$ (11)
Projected benefit obligations in excess of plan assets	(9.9)	(11)
Accumulated benefit obligation	(9.9)	(11)
Projected benefit obligation for long-term service awards	$ 0.1	$ 0.1

Pension and Other Employee B103

Pension and Other Employee Benefits - Schedule of Reconciliation of Benefit Obligations, Plan Assets Funded Status (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Other Liabilities Disclosure [Abstract]
Benefit obligation at beginning of year	$ (11)	$ (10)	$ (10.3)
Service cost	0	0	0
Interest cost	(0.1)	(0.2)	(0.3)
Plan participants’ contributions	0	0	0
Actuarial gain (loss)	1.5	(1.2)	(0.9)
Foreign exchange gain	(0.6)	0.1	1.2
Benefits paid	0.3	0.3	0.3
Benefit obligation at end of year	(9.9)	(11)	(10)
Plan assets	0	0	0
Benefit obligation at end of year	$ (9.9)	$ (11)	$ (10)

Pension and Other Employee B104

Pension and Other Employee Benefits - Components of Net Periodic Benefit Cost and Related Actuarial Assumptions (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Other Liabilities Disclosure [Abstract]
Service cost	$ 0	$ 0	$ 0
Interest cost	0.1	0.4	0.3
Expected return on plan assets	0	0	0
Amortization of prior service cost		0	0
Recognized net actuarial gain	0.4	(0.2)	0
Net periodic benefit cost	$ 0.5	$ 0.2	$ 0.3

Pension and Other Employee B105

Pension and Other Employee Benefits - Schedule of Weighted-Average Net Periodic Benefit Cost Assumptions (Detail)	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate	2.15%	1.30%	2.05%
Expected return on plan assets	0.00%	0.00%	0.00%
Rate of compensation increase	0.00%	0.00%	0.00%

Pension and Other Employee B106

Pension and Other Employee Benefits - Schedule of Expected Pension Benefit (Detail) $ in Millions	Sep. 30, 2017USD ($)
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2,017	$ 0.4
2,018	0.4
2,019	0.4
2,020	0.4
2,021	0.4
2023 to 2027	$ 2.2

Quarterly Statement of Opera107

Quarterly Statement of Operations Information (Unaudited) - (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 24, 2016	Jun. 25, 2016	Mar. 26, 2016	Dec. 26, 2015	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 802.9	$ 806.1	$ 715.4	$ 734.4	$ 726.8	$ 717.4	$ 693.3	$ 695.2	$ 3,058.8	$ 2,832.7	$ 2,705
Gross profit	417.9	409.6	388.7	404.8	406.1	393.1	385	379.1	1,621	1,563.3	1,432.7
Net income	$ 82.7	$ 59.5	$ 526.8	$ 86.5	$ 92.2	$ 84.8	$ 68.9	$ 84.9	$ 755.5	$ 330.8	$ 131.6
Diluted net income per common share (in dollars per share)	$ 0.29	$ 0.21	$ 1.84	$ 0.30	$ 0.33	$ 0.30	$ 0.24	$ 0.29	$ 2.64	$ 1.16	$ 0.45

Quarterly Statement of Opera108

Quarterly Statement of Operations Information (Unaudited) - (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended							12 Months Ended
	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 24, 2016	Mar. 26, 2016	Dec. 26, 2015	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Quarterly Financial Information Disclosure [Abstract]
Restructuring charges	$ 2.5	$ 6	$ 1.6	$ 3.2	$ 2.9	$ 3.8	$ 2.3	$ 13.3	$ 10.5	$ 28.5
Acquisition charges			19.4	$ 2.6
Gain on sale of investments			$ 899.7				$ 25.1	5.6	25.1	0
Debt extinguishment loss	$ (0.6)	$ 2.6			0.8	$ 4.5		3.2	$ 5.3	$ 62.7
Gain on sale of cost-method investments								$ 2
Other-than-temporary impairment charge					$ 1.1