Annual report pursuant to Section 13 and 15(d)

Business Summary And Significant Accounting Policies (Book Value Of Land And Mineral Rights Disclosure) (Details)

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Business Summary And Significant Accounting Policies (Book Value Of Land And Mineral Rights Disclosure) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Business Summary And Significant Accounting Policies [Abstract]    
Land rights $ 37.3 $ 36.8
Mineral rights:    
Cost 7,881.6 2,983.1
Less depletion 533.9 376.4
Net mineral rights $ 7,347.7 $ 2,606.7