XML 44 R61.htm IDEA: XBRL DOCUMENT v2.4.0.6
ASSET RETIREMENT OBLIGATION: (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
item
Dec. 31, 2011
Y
ASSET RETIREMENT OBLIGATION:    
Period after which the law requires a first review (in years)   3
Period after which successive reviews are required by the law (in years)   5
Accepted value of the Lima office building $ 17  
Annual Guarantees 10.5  
Number of units with future closure costs recognized as an asset retirement obligation 3  
Increase to net property due to closure of mine 20.3  
Asset retirement obligation activity    
Balance at the beginning of the period 62.0 59.1
Changes in estimates 27.4  
Additions 25.1  
Closure payments (0.3) (0.5)
Accretion expense 4.0 3.4
Balance at the end of the period $ 118.2 $ 62.0