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Pensions And Other Postretirement Benefits (Narrative) (Details) (USD $)
 1 Months Ended 12 Months Ended 12 Months Ended
Feb. 28, 2010
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2011
Pension Benefits [Member]
Dec. 31, 2010
Pension Benefits [Member]
Dec. 31, 2009
Pension Benefits [Member]
Dec. 31, 2011
Other Benefits [Member]
Dec. 31, 2010
Other Benefits [Member]
Dec. 31, 2011
SEI Opportunity Collective Fund [Member]
Dec. 31, 2011
SEI Special Situations Fund [Member]
Dec. 31, 2011
Structured Credit [Member]
Dec. 31, 2011
Real Estate [Member]
Dec. 31, 2011
North American Coal [Member]
Dec. 31, 2010
North American Coal [Member]
Dec. 31, 2009
North American Coal [Member]
Dec. 31, 2011
Defined Benefit Postretirement Health Coverage [Member]
United States Postretirement Benefit Plans Of U S Entity Defined Benefit [Member]
Prior To Age 65 [Member]
Dec. 31, 2011
Defined Benefit Postretirement Health Coverage [Member]
United States Postretirement Benefit Plans Of U S Entity Defined Benefit [Member]
After Age 65 [Member]
Dec. 31, 2011
Defined Benefit Postretirement Health Coverage [Member]
Northshore [Member]
After Age 65 [Member]
Dec. 31, 2011
United States [Member]
Pension Benefits [Member]
Dec. 31, 2010
United States [Member]
Pension Benefits [Member]
Dec. 31, 2011
United States [Member]
Other Benefits [Member]
Dec. 31, 2010
United States [Member]
Other Benefits [Member]
Dec. 31, 2011
Canada [Member]
Dec. 31, 2011
Canada [Member]
Pension Benefits [Member]
Dec. 31, 2010
Canada [Member]
Pension Benefits [Member]
Dec. 31, 2011
Canada [Member]
Other Benefits [Member]
Dec. 31, 2010
Canada [Member]
Other Benefits [Member]
Dec. 31, 2011
Lower Limit [Member]
Dec. 31, 2011
Lower Limit [Member]
Defined Benefit Postretirement Health Coverage [Member]
Northshore [Member]
Prior To Age 65 [Member]
Dec. 31, 2011
Upper Limit [Member]
Dec. 31, 2011
Upper Limit [Member]
Defined Benefit Postretirement Health Coverage [Member]
Northshore [Member]
Prior To Age 65 [Member]
Defined Benefit Plan Disclosure [Line Items]                                                              
Remaining interest percentage 73.20%                                                            
Number of USW Employees   2,400                                                          
Percentage of total workforce under labor contract   32.00%                     11.00%                                    
Annual limit on medical coverage for each participant                               $ 7,000 $ 3,000 $ 2,000                     $ 4,020   $ 4,500
Minimum participants percentage   15.00%                                                          
Contribution rate per hour worked                         6.50 6.42 5.27                                
Annual costs for defined contribution plan       5,700,000 4,200,000 2,100,000             9,500,000 10,300,000 6,100,000                                
Funding of bargaining unit pension plans and VEBAs   90,000,000                                                          
Accumulated benefit obligation for defined benefit pension plans   1,114,700,000 997,200,000                                                        
Redemption request notice period, days                 65 95 90 45                                      
Discount rate             4.28% 5.11%                     4.28% 5.11% 4.28% 5.11% 4.00% 4.00% 5.00% 4.25% 5.00% 4.12%   4.43%  
Investment Commitments Reserved   13,000,000                                                          
Reserved investment commitments   10,500,000                                                          
Contributions by participants to other benefit plans             $ 4,600,000 $ 6,200,000