PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Narrative) (Details) (USD $)
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12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | 12 Months Ended | |||||||||||||||||||||||||||
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Dec. 31, 2012
employee
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Dec. 31, 2011
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Dec. 31, 2012
Sei Opportunity Collective Fund [Member]
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Dec. 31, 2012
Sei Special Situations Fund [Member]
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Dec. 31, 2012
Structured Finance [Member]
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Dec. 31, 2012
Real Estate [Member]
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Dec. 31, 2012
Pension Benefits [Member]
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Dec. 31, 2011
Pension Benefits [Member]
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Dec. 31, 2010
Pension Benefits [Member]
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Dec. 31, 2012
Other Benefits [Member]
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Dec. 31, 2011
Other Benefits [Member]
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Dec. 31, 2012
Northshore [Member]
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Dec. 31, 2012
North American Coal [Member]
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Dec. 31, 2011
North American Coal [Member]
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Dec. 31, 2010
North American Coal [Member]
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Dec. 31, 2012
Defined Benefit Postretirement Health Coverage [Member]
United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Prior To Age65 [Member]
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Dec. 31, 2012
Defined Benefit Postretirement Health Coverage [Member]
United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
After Age65 [Member]
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Dec. 31, 2012
Defined Benefit Postretirement Health Coverage [Member]
Northshore [Member]
After Age65 [Member]
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Dec. 31, 2012
Minimum [Member]
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Dec. 31, 2012
Minimum [Member]
Defined Benefit Postretirement Health Coverage [Member]
Northshore [Member]
Prior To Age65 [Member]
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Dec. 31, 2012
Maximum [Member]
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Dec. 31, 2011
Maximum [Member]
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Dec. 31, 2012
Maximum [Member]
Defined Benefit Postretirement Health Coverage [Member]
Northshore [Member]
Prior To Age65 [Member]
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Dec. 31, 2012
United States [Member]
Pension Benefits [Member]
security
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Dec. 31, 2011
United States [Member]
Pension Benefits [Member]
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Dec. 31, 2012
United States [Member]
Other Benefits [Member]
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Dec. 31, 2011
United States [Member]
Other Benefits [Member]
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Dec. 31, 2012
Canada [Member]
Pension Benefits [Member]
security
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Dec. 31, 2011
Canada [Member]
Pension Benefits [Member]
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Dec. 31, 2012
Canada [Member]
Other Benefits [Member]
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Dec. 31, 2011
Canada [Member]
Other Benefits [Member]
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Feb. 28, 2010
Wabush [Member]
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Defined Benefit Plan Disclosure [Line Items] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Remaining interest percentage prior to acquisition | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 100.00% | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 73.20% |
Term of labor contracts with USW | 37 months | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Number of USW employees covered by labor contracts | 2,400 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Percentage of total workforce covered by labor contract | 32.00% | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 11.00% | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Annual limit on medical coverage for each participant | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 7,000 | $ 3,000 | $ 2,000 | Ìý | $ 4,020 | Ìý | Ìý | $ 4,500 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Minimum participants percentage | 15.00% | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Contribution rate per hour worked | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 8.10 | 6.50 | 6.42 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Annual costs for defined contribution plan | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 6,700,000 | 5,700,000 | 4,200,000 | Ìý | Ìý | Ìý | 14,900,000 | 9,500,000 | 10,300,000 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Funding of bargaining unit pension plans and VEBAs | 65,700,000 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Accumulated benefit obligation for defined benefit pension plans | 1,204,700,000 | 1,114,700,000 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Discount rate | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 3.54% | Ìý | Ìý | 3.80% | Ìý | 3.70% | 4.28% | 3.70% | 4.28% | 3.75% | 4.00% | 4.00% | 4.25% | Ìý |
Projected yield, number of bonds used | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 506 | Ìý | Ìý | Ìý | 240 | Ìý | Ìý | Ìý | Ìý |
Maturity period of security | 10 years | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Expected period of long-term return on assets | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 3 years | Ìý | 5 years | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Redemption request notice period, days | Ìý | Ìý | 65 days | 95 days | 90 days | 45 days | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Withdrawal request notice period, days | Ìý | Ìý | Ìý | Ìý | Ìý | 65 days | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Reserve for investment commitments | 10,700,000 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
Participant contributions | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 0 | $ 0 | Ìý | $ 4,600,000 | $ 4,600,000 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |