Marketable Securities Schedule of Available for Sale Securities (Details) $ in Millions	Sep. 28, 2018 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 317.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.1
Available-for-sale Securities	316.9
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	65.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0
Available-for-sale Securities	65.0
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	216.1
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.1
Available-for-sale Securities	216.0
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	2.8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0
Available-for-sale Securities	2.8
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	33.1
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0
Available-for-sale Securities	$ 33.1

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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