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Income Taxes - Activity of Company's Unrecognized Income Tax Benefits (Detail) - USD ($) $ in Millions | 12 Months Ended
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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 | 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) | (6.0)
Lapses in statutes of limitations | (19.9) | (3.2)
Acquired tax positions: |  |
Additions related to reserves acquired from acquisitions | 2.6 | 0.0
Balance as of the end of the fiscal year | $ 90.3 | $ 163.6

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- Definition Unrecognized tax benefits increases. + References No definition available. + Details
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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=65882285&loc=SL6600010-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Unrecognized Tax Benefit -URI http://asc.fasb.org/extlink&oid=6527854 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=65882285&loc=SL6600010-109319 + Details
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