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PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Narrative) (Details) (USD $)
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12 Months Ended |
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Dec. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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| Defined Benefit Plan Disclosure [Line Items] |
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| Current Fiscal Year End Date |
--12-31
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| Minimum participants percentage |
15.00%
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| Accumulated benefit obligation for defined benefit pension plans |
$ 1,091,400,000
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$ 1,204,700,000
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| Maturity period of security |
10 years
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| Reserve for investment commitments |
8,700,000
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Sei Special Situations Fund [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Redemption request notice period, days |
95 days
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Structured Finance [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Redemption request notice period, days |
90 days
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Real Estate [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Redemption request notice period, days |
45 days
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| Withdrawal request notice period, days |
65 days
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Pension Benefits [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Defined Benefit Plan, Net Periodic Benefit Cost |
52,100,000
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55,200,000
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37,800,000
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| Annual costs for defined contribution plan |
6,800,000
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6,700,000
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5,700,000
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| Participant contributions |
0
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0
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| Other Postretirement Benefit Expense |
17,400,000
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28,100,000
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26,800,000
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| Pension and Other Postretirement Benefit Expense |
76,300,000
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90,000,000
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70,300,000
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Other Benefits [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Defined Benefit Plan, Net Periodic Benefit Cost |
17,400,000
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28,100,000
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26,800,000
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| Participant contributions |
5,600,000
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4,600,000
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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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| Defined Benefit Plan Disclosure [Line Items] |
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| Annual limit on medical coverage for each participant |
7,000
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Defined Benefit Postretirement Health Coverage [Member] | United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member] | After Age65 [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Annual limit on medical coverage for each participant |
3,000
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Defined Benefit Postretirement Health Coverage [Member] | Northshore [Member] | After Age65 [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Annual limit on medical coverage for each participant |
2,000
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Minimum [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Discount rate |
4.36%
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| Expected period of long-term return on assets |
3 years
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Minimum [Member] | Defined Benefit Postretirement Health Coverage [Member] | Northshore [Member] | Prior To Age65 [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Annual limit on medical coverage for each participant |
4,020
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Maximum [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Discount rate |
4.66%
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| Expected period of long-term return on assets |
5 years
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Maximum [Member] | Defined Benefit Postretirement Health Coverage [Member] | Northshore [Member] | Prior To Age65 [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Annual limit on medical coverage for each participant |
4,500
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United States [Member] | Pension Benefits [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Discount rate |
4.57%
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3.70%
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| Projected yield, number of bonds used |
494
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United States [Member] | Other Benefits [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Discount rate |
4.57%
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3.70%
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Canada [Member] | Pension Benefits [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Discount rate |
4.50%
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3.75%
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| Projected yield, number of bonds used |
334
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Canada [Member] | Other Benefits [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Discount rate |
4.75%
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4.00%
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Tilden, Empire, Hibbing and United Taconite [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Term of labor contracts with USW |
37 months
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| Number of USW employees covered by labor contracts |
2,400
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| Percentage of total workforce covered by labor contract |
32.00%
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| Funding of bargaining unit pension plans and VEBAs |
65,700,000
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Bloom Lake [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Term of labor contracts with USW |
3 years
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Pointe Noire [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Term of labor contracts with USW |
6 years
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| Increased in Cost of Employment over Life of Union Contract |
26.00%
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Pinnacle Complex and Oak Grove [Member]
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| Defined Benefit Plan Disclosure [Line Items] |
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| Number of USW employees covered by labor contracts |
800
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| Percentage of total workforce covered by labor contract |
11.00%
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| Contribution rate per hour worked |
8.10
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8.10
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6.50
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| Annual costs for defined contribution plan |
14,900,000
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14,900,000
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9,500,000
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| Underfunded Liability Estimate |
$ 342,000,000
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