Annual report pursuant to Section 13 and 15(d)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Additional Information) (Details)

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PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Additional Information) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Pension Benefits [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Effect of change in mine ownership & noncontrolling interest $ 54.8 $ 53.3 $ 49.9
Actual return on plan assets 92.5 10.8 87.1
Other Benefits [Member]
     
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Effect of change in mine ownership & noncontrolling interest 8.6 12.5 10.7
Actual return on plan assets $ 26.1 $ 1.9 $ 20.1