Marketable Securities (Details) - USD ($) $ in Millions	Dec. 28, 2018	Sep. 28, 2018
Schedule of Available-for-sale Securities [Line Items]
Current	$ 13.4	$ 294.1
Noncurrent	2.7	22.8
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Current	7.9	65.0
Noncurrent	0.0	0.0
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Current	1.4	204.1
Noncurrent	0.0	12.0
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Current	2.2	2.0
Noncurrent	2.7	0.8
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Current	1.9	23.0
Noncurrent	$ 0.0	$ 10.0

Amount of investments in debt securities classified as available-for-sale, expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562

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Total of debt securities categorized neither as held-to-maturity nor trading which are intended be sold or mature more than one year from the balance sheet date or operating cycle, if longer.

+ References

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