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, 2011
Dec. 31, 2010
Dec. 31, 2009
Pension Benefits [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Effect of change in mine ownership & noncontrolling interest $ 53.3 $ 49.9 $ 50.9
Actual return on plan assets 10.8 87.1 63.0
Other Benefits [Member]
     
Defined Benefit Plan Disclosure [Line Items]      
Effect of change in mine ownership & noncontrolling interest 12.5 10.7 10.1
Actual return on plan assets $ 1.9 $ 20.1 $ 27.8