Annual report pursuant to Section 13 and 15(d)

ACQUISITIONS - Consideration (Details)

v3.20.4
ACQUISITIONS - Consideration (Details)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 09, 2020
USD ($)
$ / shares
shares
Mar. 13, 2020
USD ($)
$ / shares
shares
Dec. 31, 2020
shares
Dec. 31, 2019
shares
Business Acquisition [Line Items]        
Cash consideration (subject to customary working capital adjustments) $ 631      
Common shares, outstanding (in shares) | shares     477,517,372 270,084,005
Series B Preferred Stock        
Business Acquisition [Line Items]        
Fair value of Cliffs issued stock 738      
ArcelorMittal USA [Member]        
Business Acquisition [Line Items]        
Fair value of settlement of a pre-existing relationship 237      
Cash consideration (subject to customary working capital adjustments) 631      
Total purchase consideration 2,596      
Payments to Acquire Businesses, Pursuant to Transaction Agreement 505      
Payments to Acquire Businesses, Purchase of JV Interest 182      
Payments to Acquire Businesses, Cash Consideration Receivable (56)      
Business Combination, Separately Recognized Transactions, Accounts Receivable 97      
Business Combination, Separately Recognized Transactions, Assets Recognized 140      
ArcelorMittal USA [Member] | Common Stock [Member]        
Business Acquisition [Line Items]        
Fair value of Cliffs issued stock $ 990      
Number of shares issued (in shares) | shares 78,186,671   78,000,000  
Share price (in dollars per share) | $ / shares $ 12.66      
ArcelorMittal USA [Member] | Series B Preferred Stock        
Business Acquisition [Line Items]        
Number of shares issued (in shares) | shares 583,273   583,273  
Share price (in dollars per share) | $ / shares $ 1,266      
AK Steel [Member]        
Business Acquisition [Line Items]        
Total purchase consideration   $ 1,535    
Share price (in dollars per share) | $ / shares   $ 4.87    
Business Combination, Consideration Transferred, Liabilities Incurred   $ 914    
Common shares, outstanding (in shares) | shares   317,000,000    
Business Acquisition, Shares Exchange Ratio   0.400    
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares   127,000,000    
AK Steel [Member] | Common Stock [Member]        
Business Acquisition [Line Items]        
Number of shares issued (in shares) | shares     127,000,000  
Business Acquisition, Shares Exchange Ratio     0.400  
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned   $ 618    
Business Combination, Consideration Transferred, Other   3    
AK Steel [Member] | ABL Facility [Member]        
Business Acquisition [Line Items]        
Business Combination, Consideration Transferred, Liabilities Incurred   590    
AK Steel [Member] | 7.50% 2023 AK Senior Notes [Member]        
Business Acquisition [Line Items]        
Business Combination, Consideration Transferred, Liabilities Incurred   $ 324