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Equity-Based Compensation Stock Options Fair Value Assumptions (Tables)
 12 Months Ended
Dec. 31, 2011
Stock Options' Fair Value Assumptions [Abstract]  
Summary of the assumptions used in determining the fair value of stock options
A summary of the assumptions used in determining the fair value of stock options follows:
 
2011
 
2010
 
2009
Expected volatility
33
%
 
31
%
 
30
%
Expected option life in years
5.5

 
5.5

 
5.5

Expected dividend yield
2.0
%
 
2.0
%
 
2.0
%
Risk-free interest rate
2.2% to 1.4%

 
2.4% to 1.3%

 
2.2% to 1.7%

Weighted-average fair value of stock options granted
$
14.56

 
$
8.98

 
$
5.14