ACCUMULATED OTHERCOMPREHENSIVE INCOME (LOSS) (Tables)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

The components of Accumulated other comprehensive loss within Cliffs shareholders’ equity and related tax effects allocated to each are shown below:

	(In Millions)
	Pre-tax Amount		Tax Benefit		After-tax Amount
As of December 31, 2020:
Postretirement benefit liability	$	(221)	$	86	$	(135)
Foreign currency translation adjustments	3		—		3
Unrealized net loss on derivative financial instruments	(1)		—		(1)
	$	(219)	$	86	$	(133)
As of December 31, 2019:
Postretirement benefit liability	$	(454)	$	138	$	(316)
Unrealized net loss on derivative financial instruments	(4)		1		(3)
	$	(458)	$	139	$	(319)
As of December 31, 2018:
Postretirement benefit liability	$	(408)	$	127	$	(281)
Unrealized net loss on derivative financial instruments	(4)		1		(3)
	$	(412)	$	128	$	(284)

The following table reflects the changes in Accumulated other comprehensive loss related to Cliffs shareholders’ equity:

	(In Millions)
	Postretirement Benefit Liability, net of tax		Foreign Currency Translation		Derivative Financial Instruments, net of tax		Accumulated Other Comprehensive Loss
December 31, 2017	$	(264)	$	225	$	—	$	(39)
Other comprehensive income (loss) before reclassifications	(43)		3		(1)		(41)
Net loss (gain) reclassified from accumulated other comprehensive loss	26		(228)		(2)		(204)
December 31, 2018	(281)		—		(3)		(284)
Other comprehensive loss before reclassifications	(57)		—		(2)		(59)
Net loss reclassified from accumulated other comprehensive loss	22		—		2		24
December 31, 2019	(316)		—		(3)		(319)
Other comprehensive income (loss) before reclassifications	163		3		(6)		160
Net loss reclassified from accumulated other comprehensive loss	18		—		8		26
December 31, 2020	$	(135)	$	3	$	(1)	$	(133)

Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]

The following table reflects the details about Accumulated other comprehensive loss components reclassified from Cliffs shareholders’ equity:

	(In Millions)
Details about Accumulated Other Comprehensive Loss Components	Amount of (Gain)/Loss Reclassified into Income, Net of Tax						Affected Line Item in the Statement of Consolidated Operations
	Year Ended December 31,
	2020		2019		2018
Amortization of pension and OPEB liability:
Prior service costs1	$	(1)	$	(1)	$	(1)	Other non-operating income
Net actuarial loss1	30		29		27		Other non-operating income
Settlements1	(6)		—		—		Other non-operating income
	23		28		26		Total before taxes
Income tax expense	(5)		(6)		—		Income tax benefit (expense)
	$	18	$	22	$	26	Net of taxes
Changes in foreign currency translation:
Gain on foreign currency translation2	$	—	$	—	$	(228)	Income (loss) from discontinued operations, net of tax
Changes in derivative financial instruments:
Commodity contracts	$	10	$	3	$	(2)	Cost of goods sold
Income tax expense	(2)		(1)		—		Income tax benefit (expense)
	$	8	$	2	$	(2)	Net of taxes
Total reclassifications for the period, net of tax	$	26	$	24	$	(204)
1 These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See NOTE 10 - PENSIONS AND OTHER POSTRETIREMENT BENEFITS for further information.
2 Represents Australian accumulated currency translation adjustments due to the liquidation of our Australian subsidiaries' net assets.