Annual report pursuant to Section 13 and 15(d)

Investments (Details)

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Investments (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Schedule of Available-for-sale Securities [Line Items]      
Amortized cost $ 169.7 $ 105.8  
Gross unrealized gains 0 0  
Gross unrealized losses (0.1) (0.1)  
Fair value (net carrying amount) 169.6 105.7  
Available-for-sale debt securities:      
Due in one year or less, amortized cost 76.7 84.8  
Due after one year through two years, amortized cost 93.0 21.0  
Total available-for-sale debt securities, amortized cost 169.7 105.8  
Due in one year or less, fair value 76.7 84.7  
Due after one year through two years, fair value 92.9 21.0  
Total available-for-sale debt securities, fair value 169.6 105.7  
Maturity of investments, maximum (in years)   2  
Sales of available-for-sale securities 125.4 0  
Redemption of available-for-sale securities 71.5 0  
Net adjustment to Unrealized investment gains (losses) on available-for-sale securities   (0.1)  
Equity contributions to other existing joint ventures 0 12.4 0.7
Dividends from its unconsolidated affiliates 0.4 2.4 0.3
Schedule of Equity Method Investments [Line Items]      
Equity loss in the Consolidated Statements of Operations (4.7) (3.0) (15.7)
Joint Venture [Member]
      
Schedule of Equity Method Investments [Line Items]      
Equity loss in the Consolidated Statements of Operations (3.8)    
US Government Agencies Debt Securities [Member]
      
Schedule of Available-for-sale Securities [Line Items]      
Amortized cost 97.7 31.0  
Gross unrealized gains 0 0  
Gross unrealized losses (0.1) 0  
Fair value (net carrying amount) 97.6 31.0  
Corporate Debt Securities [Member]
      
Schedule of Available-for-sale Securities [Line Items]      
Amortized cost 51.7 44.5  
Gross unrealized gains 0 0  
Gross unrealized losses 0 (0.1)  
Fair value (net carrying amount) 51.7 44.4  
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
      
Schedule of Available-for-sale Securities [Line Items]      
Amortized cost 19.5 29.5  
Gross unrealized gains 0 0  
Gross unrealized losses 0 0  
Fair value (net carrying amount) 19.5 29.5  
US Treasury Securities [Member]
      
Schedule of Available-for-sale Securities [Line Items]      
Amortized cost 0.8 0.8  
Gross unrealized gains 0 0  
Gross unrealized losses 0 0  
Fair value (net carrying amount) $ 0.8 $ 0.8