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STOCK-BASED COMPENSATION (Tables)
6 Months Ended
Jun. 30, 2011
STOCK-BASED COMPENSATION [Abstract]  
Stock-based compensation expense
Stock-based compensation granted includes stock options, performance stock awards, restricted stock awards, and deferred directors’ compensation.  Stock-based compensation expense was as follows:

   
Three Months Ended
June 30,
   
Six Months Ended
June 30,
 
   
2011
   
2010
   
2011
   
2010
 
   
($ in millions)
   
($ in millions)
 
Stock-based compensation
 
$
2.7
   
$
3.7
   
$
4.8
   
$
5.7
 
Mark-to-market adjustments
   
(0.1
)
   
(0.6
)
   
0.8
     
0.2
 
Total expense
 
$
2.6
   
$
3.1
   
$
5.6
   
$
5.9
 
Schedule of fair value of stock options granted
The fair value of each stock option granted, which typically vests ratably over three years, but not less than one year, was estimated on the date of grant, using the Black-Scholes option-pricing model with the following weighted-average assumptions:

Grant date
 
2011
   
2010
 
Dividend yield
   
4.32
%
   
4.32
%
Risk-free interest rate
   
3.05
%
   
3.00
%
Expected volatility
   
42
%
   
42
%
Expected life (years)
   
7.0
     
7.0
 
Grant fair value (per option)
 
$
5.48
   
$
4.61
 
Exercise price
 
$
18.78
   
$
15.68
 
Shares granted
   
575,000
     
803,750