Cleveland-Cliffs Inc. Quarterly report pursuant to Section 13 or 15(d)

DEBT AND CREDIT FACILITIES DEBT AND CREDIT FACILITIES (Schedule of Extinguishment of Debt) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	$ 714.0	$ 15.5	$ 724.0	$ 15.5
Gain (loss) on extinguishment of debt	17.9	(0.2)	18.2	(0.2)
$700 Million 4.875% 2021 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	114.0	13.2	124.0	13.2
Gain (loss) on extinguishment of debt	(5.0)	(0.1)	(5.3)	(0.1)
$1.075 Billion 5.75% 2025 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	600.0	1.7	600.0	1.7
Gain (loss) on extinguishment of debt	$ (12.9)	(0.1)	$ (12.9)	(0.1)
$400 million 5.90% 2020 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount		0.5		0.5
Gain (loss) on extinguishment of debt		0.0		0.0
$500 Million 4.80% 2020 Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount		0.1		0.1
Gain (loss) on extinguishment of debt		$ 0.0		$ 0.0