Cleveland-Cliffs Inc. Annual report pursuant to Section 13 and 15(d)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Target Allocation and Actual Asset Allocations for Pension and VEBA Plan Assets) (Details)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Target Allocation and Actual Asset Allocations for Pension and VEBA Plan Assets) (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	100.00%	100.00%
Defined Benefit Plan, Target Plan Asset Allocations	100.00%
Pension Benefits [Member] \| Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	48.60%	51.50%
Defined Benefit Plan, Target Plan Asset Allocations	48.20%
Pension Benefits [Member] \| Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	29.00%	26.70%
Defined Benefit Plan, Target Plan Asset Allocations	28.40%
Pension Benefits [Member] \| Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	6.20%	6.30%
Defined Benefit Plan, Target Plan Asset Allocations	6.10%
Pension Benefits [Member] \| Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	3.30%	3.20%
Defined Benefit Plan, Target Plan Asset Allocations	5.50%
Pension Benefits [Member] \| Structured Finance [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	6.90%	6.70%
Defined Benefit Plan, Target Plan Asset Allocations	5.90%
Pension Benefits [Member] \| Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	5.30%	4.50%
Defined Benefit Plan, Target Plan Asset Allocations	5.90%
Pension Benefits [Member] \| Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	0.70%	1.10%
Defined Benefit Plan, Target Plan Asset Allocations	0.00%
Veba Trust [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	100.00%	100.00%
Defined Benefit Plan, Target Plan Asset Allocations	100.00%
Veba Trust [Member] \| Equity Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	8.60%	10.40%
Defined Benefit Plan, Target Plan Asset Allocations	8.00%
Veba Trust [Member] \| Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	79.30%	66.60%
Defined Benefit Plan, Target Plan Asset Allocations	80.10%
Veba Trust [Member] \| Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	4.30%	9.80%
Defined Benefit Plan, Target Plan Asset Allocations	4.20%
Veba Trust [Member] \| Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	2.30%	2.40%
Defined Benefit Plan, Target Plan Asset Allocations	2.60%
Veba Trust [Member] \| Structured Finance [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	2.30%	5.40%
Defined Benefit Plan, Target Plan Asset Allocations	2.10%
Veba Trust [Member] \| Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	3.20%	5.30%
Defined Benefit Plan, Target Plan Asset Allocations	3.00%
Veba Trust [Member] \| Cash [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocation	0.00%	0.10%
Defined Benefit Plan, Target Plan Asset Allocations	0.00%