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

PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Additional Information) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Effect of change in mine ownership & noncontrolling interest	$ 51.4	$ 46.5	$ 54.8
Actual return on plan assets	78.7	109.5	92.5
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Effect of change in mine ownership & noncontrolling interest	5.9	4.8	8.6
Actual return on plan assets	$ 31.9	$ 11.0	$ 26.1