Annual report [Section 13 and 15(d), not S-K Item 405]

BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)

v3.25.4
BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)
$ / shares in Units, $ in Millions
12 Months Ended
Nov. 01, 2024
$ / shares
shares
Dec. 31, 2025
USD ($)
employee
segment
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Nov. 01, 2024
$ / shares
Basis of Presentation and Significant Accounting Policies [Line Items]          
Number of employees | employee   25,000      
Amount of employees represented by a union, percent   90.00%      
Number of employees represented by a union | employee   20,000      
Number of operating segments | segment   4      
Number of reportable segments | segment   1      
Cost of goods sold   $ 19,470 $ 19,122 $ 20,623  
Income tax benefit (expense)   (581) (236) 144  
Accrued employment costs   517 486    
Deferred income taxes   375 849    
Retained earnings (deficit)   (529) 949    
Revision of Prior Period, Adjustment          
Basis of Presentation and Significant Accounting Policies [Line Items]          
Cost of goods sold     7 18  
Income tax benefit (expense)     1 $ 4  
Accrued employment costs     39    
Deferred income taxes     9    
Retained earnings (deficit)     30    
Stelco Holdings Inc          
Basis of Presentation and Significant Accounting Policies [Line Items]          
Share price (in dollars per share) | (per share) $ 60.00       $ 13.27
Common stock per share | shares 25,862,021        
Business Acquisition, Shares Exchange Ratio 0.454        
Stelco Holdings Inc | Stelco Holdings Inc          
Basis of Presentation and Significant Accounting Policies [Line Items]          
Share price (in dollars per share) | $ / shares $ 60.00        
Other non-current assets          
Basis of Presentation and Significant Accounting Policies [Line Items]          
Investment in affiliates   $ 132 $ 131