Quarterly report pursuant to Section 13 or 15(d)

ACQUISITIONS - ArcelorMittal USA Consideration (Details)

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ACQUISITIONS - ArcelorMittal USA Consideration (Details) - ArcelorMittal USA - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Dec. 09, 2020
Mar. 31, 2021
Business Acquisition [Line Items]    
Fair value of settlement of a pre-existing relationship $ 237  
Cash consideration 635  
Consideration transferred 2,600  
Cash consideration pursuant to the AM USA Transaction Agreement 505  
Cash consideration for purchase of the remaining JV partner's interest of Kote and Tek 182  
Estimated total cash consideration receivable (52)  
Accounts receivable 97  
Freestanding derivative asset from customer supply agreement 140  
Common Stock    
Business Acquisition [Line Items]    
Fair value of shares issued $ 990  
Stock issued during period, shares, acquisitions (in shares) 78,186,671  
Price per share of Cliffs common shares (in dollars per share) $ 12.66  
Series B Preferred Stock    
Business Acquisition [Line Items]    
Fair value of shares issued $ 738  
Stock issued during period, shares, acquisitions (in shares) 583,273 583,273
Price per share of Cliffs common shares (in dollars per share) $ 1,266