Cash Equivalents and Investments (Available for sales securities) (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 29, 2017		Sep. 30, 2016	Sep. 29, 2017		Sep. 30, 2016	Dec. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value		$ 179.3			$ 179.3			$ 133.3
Cash Equivalents		25.1			25.1			22.2
Short-term investments		154.2			154.2			111.1
Available-for-sale Debt Securities, Amortized Cost		179.3			179.3			133.3
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Securities		0.0		$ 0.0	0.1		$ 0.0
Available-for-sale Securities, Gross Realized Gain (Loss)		0.5			1.5
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	11.6			11.6			11.7
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	2.1			2.1
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	0.0			0.0			10.0
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	72.1			72.1			31.7
Bank Time Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Time Deposits	[1]	0.0			0.0			2.4
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	93.5			93.5			77.5
Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value		179.3			179.3			133.3
Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	11.6			11.6			11.7
Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value		2.1	[1]		2.1	[1]		0.0
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value		0.0			0.0			10.0	[1]
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	72.1			72.1			31.7
Fair Value, Inputs, Level 2 [Member] | Bank Time Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Time Deposits		0.0			0.0			2.4	[1]
Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	$ 93.5			$ 93.5			$ 77.5

[1] The Company’s available-for sale securities are valued using readily available pricing sources for comparable instruments, or model-driven valuations using significant inputs derived from or corroborated by observable market data, including yield curves and credit ratings.