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. 28, 2013
Sep. 29, 2012
Sep. 28, 2013
Sep. 29, 2012
Dec. 31, 2012
Schedule of Investments [Line Items]          
Maturity Of Investments, Maximum     2 years    
Amortized cost $ 22.3   $ 22.3   $ 144.4
Gross Unrealized Gains, Available-for-sale Securities 0   0   0
Gross Unrealized Losses, Available-for-sale Securities 0   0   0
Fair value (net carrying amount) 22.3   22.3   144.4
Available-for-sale debt securities [Abstract]          
Due in one year or less, amortized cost 22.3   22.3   92.3
Due after one year through two years, amortized cost         52.1
Total available-for-sale debt securities, amortized cost 22.3   22.3   144.4
Due in one year or less, fair value (net carrying amount) 22.3   22.3   92.3
Due after one year through two years, fair value (net carrying amount)         52.1
Total available-for-sale debt securities, fair value (net carrying amount) 22.3   22.3   144.4
Redemptions of available-for-sale securities     107.4 137.7  
Sales of available-for-sale securities     35.7 41.9  
Net adjustment to unrealized investment losses on available-for-sale securities 0 0.1 0 0.1  
Agency Bonds [Member]
          
Schedule of Investments [Line Items]          
Amortized cost         59.2
Gross Unrealized Gains, Available-for-sale Securities         0
Gross Unrealized Losses, Available-for-sale Securities         0
Fair value (net carrying amount)         59.2
Corporate Bonds [Member]
          
Schedule of Investments [Line Items]          
Amortized cost 21.5   21.5   66.4
Gross Unrealized Gains, Available-for-sale Securities 0   0   0
Gross Unrealized Losses, Available-for-sale Securities 0   0   0
Fair value (net carrying amount) 21.5   21.5   66.4
Commercial Paper [Member]
          
Schedule of Investments [Line Items]          
Amortized cost         16.0
Gross Unrealized Gains, Available-for-sale Securities         0
Gross Unrealized Losses, Available-for-sale Securities         0
Fair value (net carrying amount)         16.0
Certificate of Deposit [Member]
          
Schedule of Investments [Line Items]          
Amortized cost         2.0
Gross Unrealized Gains, Available-for-sale Securities         0
Gross Unrealized Losses, Available-for-sale Securities         0
Fair value (net carrying amount)         2.0
U.S. Treasury Bills [Member]
          
Schedule of Investments [Line Items]          
Amortized cost 0.8   0.8   0.8
Gross Unrealized Gains, Available-for-sale Securities 0   0   0
Gross Unrealized Losses, Available-for-sale Securities 0   0   0
Fair value (net carrying amount) $ 0.8   $ 0.8   $ 0.8