Cash Equivalents and Investments (Available for sales securities) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jul. 01, 2016	Jun. 30, 2017	Jul. 01, 2016	Dec. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value		$ 114.4		$ 114.4		$ 133.3
Cash Equivalents		13.2		13.2		22.2
Short-term investments		101.2		101.2		111.1
Available-for-sale Debt Securities, Amortized Cost		114.4		114.4		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)		0.0
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value	[1]	11.7		11.7		11.7
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]	73.9		73.9		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]	28.8		28.8		77.5
Fair Value, Inputs, Level 2 [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Securities, Fair Value		114.4		114.4		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]	11.7		11.7		11.7
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	[1]	0.0		0.0		10.0
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]	73.9		73.9		31.7
Fair Value, Inputs, Level 2 [Member] | Bank Time Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Time Deposits	[1]	0.0		0.0		2.4
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]	$ 28.8		$ 28.8		$ 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.