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. 29, 2012
Oct. 01, 2011
Sep. 29, 2012
Oct. 01, 2011
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]          
Maturity of investments, maximum (in years)     2 years    
Amortized cost $ 145.1   $ 145.1   $ 169.7
Gross unrealized gains 0   0   0
Gross unrealized losses 0   0   (0.1)
Fair value (net carrying amount) 145.1   145.1   169.6
Available-for-sale debt securities [Abstract]          
Due in one year or less, amortized cost 97.5   97.5   76.7
Due after one year through two years, amortized cost 47.6   47.6   93.0
Total available-for-sale debt securities, amortized cost 145.1   145.1   169.7
Due in one year or less, fair value (net carrying amount) 97.5   97.5   76.7
Due after one year through two years, fair value (net carrying amount) 47.6   47.6   92.9
Total available-for-sale debt securities, fair value (net carrying amount) 145.1   145.1   169.6
Sales of available-for-sale securities     41.9 98.0  
Redemptions of available-for-sale securities     137.7 65.0  
Net adjustment to unrealized investment losses on available-for-sale securities 0.1 (0.1) 0.1 (0.2)  
Agency Bonds [Member]
         
Schedule of Available-for-sale Securities [Line Items]          
Amortized cost 47.6   47.6   97.7
Gross unrealized gains 0   0   0
Gross unrealized losses 0   0   (0.1)
Fair value (net carrying amount) 47.6   47.6   97.6
Corporate Bonds [Member]
         
Schedule of Available-for-sale Securities [Line Items]          
Amortized cost 73.7   73.7   51.7
Gross unrealized gains 0   0   0
Gross unrealized losses 0   0   0
Fair value (net carrying amount) 73.7   73.7   51.7
Commercial Paper [Member]
         
Schedule of Available-for-sale Securities [Line Items]          
Amortized cost 23.0   23.0   19.5
Gross unrealized gains 0   0   0
Gross unrealized losses 0   0   0
Fair value (net carrying amount) 23.0   23.0   19.5
U.S. Treasury Bills [Member]
         
Schedule of Available-for-sale Securities [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