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

DEBT AND CREDIT FACILITIES (Debt Extinguishment) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Extinguishment of Debt [Line Items]
Debt Extinguished			$ 227.4	$ 1,610.7
Gain (loss) on extinguishment of debt			(6.8)	(165.4)	$ 166.3
Debt redemption premiums paid		$ 17.4	7.1	110.0
$540 Million 8.25% 2020 First Lien Notes
Extinguishment of Debt [Line Items]
Debt Extinguished	$ 35.6			540.0
Gain (loss) on extinguishment of debt				(93.5)
$218.5 Million 8.00% 2020 1.5 Lien Notes
Extinguishment of Debt [Line Items]
Debt Extinguished				218.5
Gain (loss) on extinguishment of debt				45.1	174.3
$544.2 Million 7.75% 2020 Second Lien Notes
Extinguishment of Debt [Line Items]
Debt Extinguished				430.1
Gain (loss) on extinguishment of debt				(104.5)	6.9
$1.075 Billion 5.75% 2025 Senior Notes
Extinguishment of Debt [Line Items]
Debt Extinguished			1.7
Gain (loss) on extinguishment of debt			0.1
$400 Million 5.90% 2020 Senior Notes
Extinguishment of Debt [Line Items]
Debt Extinguished			88.9	136.7
Gain (loss) on extinguishment of debt			(3.3)	(7.8)	28.3
$500 Million 4.80% 2020 Senior Notes
Extinguishment of Debt [Line Items]
Debt Extinguished			122.4	114.4
Gain (loss) on extinguishment of debt			(3.7)	(1.9)	19.5
$700 Million 4.875% 2021 Senior Notes
Extinguishment of Debt [Line Items]
Debt Extinguished			14.4	171.0
Gain (loss) on extinguishment of debt			$ 0.1	$ (2.8)	$ 33.3