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 6 Months Ended
Jun. 29, 2013
Jun. 30, 2012
Jun. 29, 2013
Jun. 30, 2012
Dec. 31, 2012
Schedule of Investments [Line Items]          
Maturity of investments, maximum     2 years    
Amortized cost $ 2.7   $ 2.7   $ 144.4
Gross unrealized gains 0   0   0
Gross unrealized losses 0   0   0
Fair value (net carrying amount) 2.7   2.7   144.4
Available-for-sale debt securities [Abstract]          
Due in one year or less, amortized cost 2.7   2.7   92.3
Due after one year through two years, amortized cost         52.1
Total available-for-sale debt securities, amortized cost 2.7   2.7   144.4
Due in one year or less, fair value (net carrying amount) 2.7   2.7   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) 2.7   2.7   144.4
Redemptions of available-for-sale securities     107.4 74.0  
Sales of available-for-sale securities     35.7 74.2  
Net adjustment to unrealized investment losses on available-for-sale securities 0 0.1 0 0  
Agency Bonds [Member]
          
Schedule of Investments [Line Items]          
Amortized cost         59.2
Gross unrealized gains         0
Gross unrealized losses         0
Fair value (net carrying amount)         59.2
Corporate Bonds [Member]
          
Schedule of Investments [Line Items]          
Amortized cost 1.9   1.9   66.4
Gross unrealized gains 0   0   0
Gross unrealized losses 0   0   0
Fair value (net carrying amount) 1.9   1.9   66.4
Commercial Paper [Member]
          
Schedule of Investments [Line Items]          
Amortized cost         16.0
Gross unrealized gains         0
Gross unrealized losses         0
Fair value (net carrying amount)         16.0
Certificate of Deposit [Member]
          
Schedule of Investments [Line Items]          
Amortized cost         2.0
Gross unrealized gains         0
Gross unrealized losses         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 0   0   0
Gross unrealized losses 0   0   0
Fair value (net carrying amount) $ 0.8   $ 0.8   $ 0.8