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Stock-Based Compensation Plans (Details 7) (USD $)
In Millions, except Per Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Summary of stock appreciation rights      
Compensation expense $ 13.7 $ 15.4 $ 12.8
Weighted-average grant date fair value $ 31.78    
Stock Appreciation Rights [Member]
     
Summary of stock appreciation rights      
Compensation expense $ 5.4 $ 4.7 $ 4.4
Weighted-average grant date fair value $ 9.39 $ 13.75 $ 10.96