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

FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value Of Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Assets:
Cash equivalents	$ 543.4	$ 616.9
Derivative Asset	91.5	37.9
Total Asset	634.9	654.8
Liabilities:
Derivative Liability	3.7	2.0
Total Liability	3.7	2.0
Fair Value, Inputs, Level 1 [Member]
Assets:
Cash equivalents	0.8	66.3
Derivative Asset	0.0	0.0
Total Asset	0.8	66.3
Liabilities:
Derivative Liability	0.0	0.0
Total Liability	0.0	0.0
Fair Value, Inputs, Level 2 [Member]
Assets:
Cash equivalents	542.6	550.6
Derivative Asset	0.1	0.0
Total Asset	542.7	550.6
Liabilities:
Derivative Liability	3.7	0.3
Total Liability	3.7	0.3
Fair Value, Inputs, Level 3 [Member]
Assets:
Cash equivalents	0.0	0.0
Derivative Asset	91.4	37.9
Total Asset	91.4	37.9
Liabilities:
Derivative Liability	0.0	1.7
Total Liability	$ 0.0	$ 1.7