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Annual report pursuant to Section 13 and 15(d)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Narrative) (Details)

v2.4.0.8
PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Narrative) (Details) (USD $)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Current Fiscal Year End Date --12-31 Ìý Ìý
Minimum participants percentage 15.00% Ìý Ìý
Accumulated benefit obligation for defined benefit pension plans $ 1,091,400,000 $ 1,204,700,000 Ìý
Maturity period of security 10 years Ìý Ìý
Reserve for investment commitments 8,700,000 Ìý Ìý
Sei Special Situations Fund [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Redemption request notice period, days 95 days Ìý Ìý
Structured Finance [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Redemption request notice period, days 90 days Ìý Ìý
Real Estate [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Redemption request notice period, days 45 days Ìý Ìý
Withdrawal request notice period, days 65 days Ìý Ìý
Pension Benefits [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Defined Benefit Plan, Net Periodic Benefit Cost 52,100,000 55,200,000 37,800,000
Annual costs for defined contribution plan 6,800,000 6,700,000 5,700,000
Participant contributions 0 0 Ìý
Other Postretirement Benefit Expense 17,400,000 28,100,000 26,800,000
Pension and Other Postretirement Benefit Expense 76,300,000 90,000,000 70,300,000
Other Benefits [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Defined Benefit Plan, Net Periodic Benefit Cost 17,400,000 28,100,000 26,800,000
Participant contributions 5,600,000 4,600,000 Ìý
Defined Benefit Postretirement Health Coverage [Member] | United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member] | Prior To Age65 [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Annual limit on medical coverage for each participant 7,000 Ìý Ìý
Defined Benefit Postretirement Health Coverage [Member] | United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member] | After Age65 [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Annual limit on medical coverage for each participant 3,000 Ìý Ìý
Defined Benefit Postretirement Health Coverage [Member] | Northshore [Member] | After Age65 [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Annual limit on medical coverage for each participant 2,000 Ìý Ìý
Minimum [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Discount rate 4.36% Ìý Ìý
Expected period of long-term return on assets 3 years Ìý Ìý
Minimum [Member] | Defined Benefit Postretirement Health Coverage [Member] | Northshore [Member] | Prior To Age65 [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Annual limit on medical coverage for each participant 4,020 Ìý Ìý
Maximum [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Discount rate 4.66% Ìý Ìý
Expected period of long-term return on assets 5 years Ìý Ìý
Maximum [Member] | Defined Benefit Postretirement Health Coverage [Member] | Northshore [Member] | Prior To Age65 [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Annual limit on medical coverage for each participant 4,500 Ìý Ìý
United States [Member] | Pension Benefits [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Discount rate 4.57% 3.70% Ìý
Projected yield, number of bonds used 494 Ìý Ìý
United States [Member] | Other Benefits [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Discount rate 4.57% 3.70% Ìý
Canada [Member] | Pension Benefits [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Discount rate 4.50% 3.75% Ìý
Projected yield, number of bonds used 334 Ìý Ìý
Canada [Member] | Other Benefits [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Discount rate 4.75% 4.00% Ìý
Tilden, Empire, Hibbing and United Taconite [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Term of labor contracts with USW 37 months Ìý Ìý
Number of USW employees covered by labor contracts 2,400 Ìý Ìý
Percentage of total workforce covered by labor contract 32.00% Ìý Ìý
Funding of bargaining unit pension plans and VEBAs 65,700,000 Ìý Ìý
Bloom Lake [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Term of labor contracts with USW 3 years Ìý Ìý
Pointe Noire [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Term of labor contracts with USW 6 years Ìý Ìý
Increased in Cost of Employment over Life of Union Contract 26.00% Ìý Ìý
Pinnacle Complex and Oak Grove [Member]
 Ìý Ìý Ìý
Defined Benefit Plan Disclosure [Line Items] Ìý Ìý Ìý
Number of USW employees covered by labor contracts 800 Ìý Ìý
Percentage of total workforce covered by labor contract 11.00% Ìý Ìý
Contribution rate per hour worked 8.10 8.10 6.50
Annual costs for defined contribution plan 14,900,000 14,900,000 9,500,000
Underfunded Liability Estimate $ 342,000,000 Ìý Ìý