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

DERIVATIVE INSTRUMENTS (Schedule Of Derivatives Not Designated As Hedging Instruments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Revenues	$ 555.6	$ 741.8	$ 1,455.8	$ 1,636.1
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Revenues	(40.9)	135.9	43.4	334.4
Not Designated as Hedging Instrument [Member] \| Customer Supply Agreement [Member] \| Revenue from Contract with Customer Benchmark [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss) recognized in income on derivative	7.6	139.7	82.2	337.1
Not Designated as Hedging Instrument [Member] \| Provisional Pricing Arrangements [Member] \| Revenue from Contract with Customer Benchmark [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain/(loss) recognized in income on derivative	$ (48.5)	$ (3.8)	$ (38.8)	$ (2.7)