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ASSET RETIREMENT OBLIGATIONS (Tables)
 9 Months Ended
Sep. 30, 2014
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of asset retirement obligations
The following table presents a reconciliation of the beginning and ending balances of asset retirement obligations at September 30, 2014 and December 31, 2013 as reported in the Balance Sheet:
($ Millions)
 
September 30,
2014
 
December 31,
2013
Asset retirement obligations, beginning of year
 
$
27.5

 
$
24.9

Liabilities incurred during the period
 
0.5

 
0.8

Liabilities settled during the period
 
(0.1
)
 
(0.1
)
Accretion
 
0.7

 
1.3

Revisions in estimated cash flows
 
(0.9
)
 
0.6

Asset retirement obligations, end of year
 
$
27.7

 
$
27.5