STOCK-BASED COMPENSATION (Tables)
 9 Months Ended
Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Stock-based compensation expense
Stock-based compensation expense was as follows:
 
Three Months Ended
September 30,
 
Nine Months Ended
September 30,
 
2014
 
2013
 
2014
 
2013
 
($ in millions)
Stock-based compensation
$
1.8

 
$
3.4

 
$
6.8

 
$
9.6

Mark-to-market adjustments
(0.8
)
 
(0.7
)
 
(1.9
)
 
0.6

Total expense
$
1.0

 
$
2.7

 
$
4.9

 
$
10.2
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
2014
 
2013
Dividend yield
3.13
%
 
3.44
%
Risk-free interest rate
2.13
%
 
1.35
%
Expected volatility
42
%
 
43
%
Expected life (years)
7.0

 
7.0

Grant fair value (per option)
$
8.30

 
$
7.05

Exercise price
$
25.57

 
$
23.28

Shares granted
589,000

 
621,000