Quarterly report pursuant to Section 13 or 15(d)

Document and Entity Information

Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Oct. 21, 2019
Cover page.    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Sep. 30, 2019  
Document Transition Report false  
Entity File Number 1-8944  
Entity Registrant Name CLEVELAND-CLIFFS INC.  
Entity Incorporation, State or Country Code OH  
Entity Tax Identification Number 34-1464672  
Entity Address, Address Line One 200 Public Square,  
Entity Address, City or Town Cleveland,  
Entity Address, State or Province OH  
Entity Address, Postal Zip Code 44114-2315  
City Area Code 216  
Local Phone Number 694-5700  
Title of 12(b) Security Common shares, par value $0.125 per share  
Trading Symbol CLF  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   270,082,088
Entity Central Index Key 0000764065  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Amendment Flag false