Annual report pursuant to Section 13 and 15(d)

ACQUISITIONS - Pro Forma (Details)

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ACQUISITIONS - Pro Forma (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
ArcelorMittal USA and AK Steel      
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]      
Revenues, pro forma   $ 12,837 $ 17,163
Net income (loss) attributable to Cliffs shareholders, pro forma   (520) (11)
Expenses, pro forma   $ 32 76
Statutory tax rate, pro forma   24.30%  
Income tax benefit (expense), pro forma   $ 170 117
ArcelorMittal USA and AK Steel | Intersegment Eliminations      
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]      
Revenues, pro forma   844 1,499
Ferrous Processing and Trading      
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]      
Revenues, pro forma $ 21,701 13,549  
Net income (loss) attributable to Cliffs shareholders, pro forma $ 3,074 (526)  
Franchise | ArcelorMittal USA and AK Steel      
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]      
Net income (loss) attributable to Cliffs shareholders, pro forma   140 129
Fair Value Adjustment to Inventory | ArcelorMittal USA and AK Steel      
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]      
Net income (loss) attributable to Cliffs shareholders, pro forma   96 362
Acquisition-related costs | ArcelorMittal USA and AK Steel      
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]      
Net income (loss) attributable to Cliffs shareholders, pro forma   93 $ 93
Restructuring Costs | ArcelorMittal USA      
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]      
Net income (loss) attributable to Cliffs shareholders, pro forma   $ 1,820