Quarterly report pursuant to Section 13 or 15(d)

ACQUISITION OF AK STEEL (Business Acquisition Table) (Details)

v3.20.1
ACQUISITION OF AK STEEL (Business Acquisition Table) (Details)
$ / shares in Units, $ in Millions
Mar. 13, 2020
USD ($)
$ / shares
shares
Mar. 31, 2020
shares
Dec. 31, 2019
shares
Business Acquisition [Line Items]      
Fair value of Cliffs common shares issued for AK Steel outstanding common stock $ 617.6    
Fair value of debt included in consideration 913.6    
Business Combination, Consideration Transferred 1,535.5    
Number of shares of AK Steel common stock issued and outstanding | shares   398,587,083 270,084,005
AK Steel Holding Corporation [Member]      
Business Acquisition [Line Items]      
Fair value of Cliffs common shares issued for AK Steel outstanding common stock 617.6    
Fair value of debt included in consideration 913.6    
Business Combination, Consideration Transferred $ 1,500.0    
Number of shares of AK Steel common stock issued and outstanding | shares 316,900,000    
Business Acquisition, Shares Exchange Ratio 0.400    
Shares of Cliffs common shares issued to AK Steel stockholders | shares 126,800,000    
Price per share of Cliffs common shares | $ / shares $ 4.87    
Credit Facility | AK Steel Holding Corporation [Member]      
Business Acquisition [Line Items]      
Fair value of debt included in consideration $ 590.0    
7.50% 2023 AK Senior Notes [Member] | AK Steel Holding Corporation [Member]      
Business Acquisition [Line Items]      
Fair value of debt included in consideration $ 323.6