Quarterly report pursuant to Section 13 or 15(d)

ACQUISITIONS - AK Steel Consideration (Details)

v3.21.2
ACQUISITIONS - AK Steel Consideration (Details)
$ / shares in Units, $ in Millions
Mar. 13, 2020
USD ($)
$ / shares
shares
Sep. 30, 2021
shares
Jun. 30, 2021
shares
Mar. 31, 2021
shares
Dec. 31, 2020
shares
Sep. 30, 2020
shares
Jun. 30, 2020
shares
Mar. 31, 2020
shares
Dec. 31, 2019
shares
Business Acquisition [Line Items]                  
Common shares, outstanding (in shares) | shares   500,055,941     477,517,372        
AK Steel                  
Business Acquisition [Line Items]                  
Fair value of debt included in consideration $ 914                
Fair value of Cliffs common shares issued for AK Steel outstanding common stock 618                
Other 3                
Consideration transferred $ 1,535                
Common shares, outstanding (in shares) | shares 317,000,000                
Exchange ratio 0.400                
Shares of Cliffs common shares issued to AK Steel stockholders (in shares) | shares 127,000,000                
Price per share of Cliffs common shares (in dollars per share) | $ / shares $ 4.87                
ABL Facility | AK Steel                  
Business Acquisition [Line Items]                  
Fair value of debt included in consideration $ 590                
7.500% Senior Secured Notes due July 2023 | AK Steel                  
Business Acquisition [Line Items]                  
Fair value of debt included in consideration 324                
Common Stock                  
Business Acquisition [Line Items]                  
Common shares, outstanding (in shares) | shares   500,000,000 500,000,000 499,000,000 478,000,000 399,000,000 399,000,000 399,000,000 271,000,000
Common Stock | AK Steel                  
Business Acquisition [Line Items]                  
Fair value of Cliffs common shares issued for AK Steel outstanding common stock $ 618                
Common Stock | AK Steel                  
Business Acquisition [Line Items]                  
Exchange ratio 0.400