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Annual report pursuant to Section 13 and 15(d)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Weighted-Average Assumptions Used to Determine Benefit Obligations) (Details)

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PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Weighted-Average Assumptions Used to Determine Benefit Obligations) (Details)
Dec. 31, 2018
Dec. 31, 2017
Salary [Member] | Pension Benefits [Member] Ìý Ìý
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Ìý Ìý
Rate of compensation increase 3.00% 3.00%
Hourly [Member] | Pension Benefits [Member] Ìý Ìý
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Ìý Ìý
Rate of compensation increase 2.00% 2.00%
Iron Hourly [Member] | Pension Benefits [Member] Ìý Ìý
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Ìý Ìý
Discount rate 4.31% 3.60%
Salaried [Member] | Pension Benefits [Member] Ìý Ìý
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Ìý Ìý
Discount rate 4.21% 3.52%
Salaried [Member] | Other Benefits [Member] Ìý Ìý
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Ìý Ìý
Discount rate 4.27% 3.57%
Ore Mining [Member] | Pension Benefits [Member] Ìý Ìý
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Ìý Ìý
Discount rate 4.33% 3.61%
Supplemental Executive Retirement Plan S E R P [Member] | Pension Benefits [Member] Ìý Ìý
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Ìý Ìý
Discount rate 4.22% 3.50%
Hourly [Member] | Other Benefits [Member] Ìý Ìý
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Ìý Ìý
Discount rate 4.29% 3.60%