Quarterly report pursuant to Section 13 or 15(d)

Investments (Details)

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Investments (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 27, 2014
Sep. 28, 2013
Sep. 27, 2014
Sep. 28, 2013
Dec. 31, 2013
Schedule of Investments [Line Items]          
Amortized cost $ 0.8 $ 22.3 $ 0.8 $ 22.3 $ 12.7
Gross unrealized gains 0 0 0 0 0
Gross unrealized losses 0 0 0 0 0
Fair value (net carrying amount) 0.8 22.3 0.8 22.3 12.7
Redemptions of available-for-sale securities     11.9 107.4  
Proceeds from sale of available-for-sale securities       35.7  
Net adjustment to unrealized investment losses on available-for-sale securities 0 0 0 0  
U.S. Treasury Bills [Member]
          
Schedule of Investments [Line Items]          
Amortized cost 0.8 0.8 0.8 0.8 0.8
Gross unrealized gains 0 0 0 0 0
Gross unrealized losses 0 0 0 0 0
Fair value (net carrying amount) 0.8 0.8 0.8 0.8 0.8
Corporate Bonds [Member]
          
Schedule of Investments [Line Items]          
Amortized cost   21.5   21.5 11.9
Gross unrealized gains   0   0 0
Gross unrealized losses   0   0 0
Fair value (net carrying amount)   $ 21.5   $ 21.5 $ 11.9