Annual report pursuant to Section 13 and 15(d)

PENSIONS AND OTHER POSTRETIREMENT BENEFITS - Multiemployer Plan (Details)

v3.20.4
PENSIONS AND OTHER POSTRETIREMENT BENEFITS - Multiemployer Plan (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Multiemployer Plan [Line Items]      
Contributions $ 30 $ 4 $ 4
Steelworkers Pension Trust      
Multiemployer Plan [Line Items]      
Pension Plan EIN 236648508    
Pension Plan Number 499    
Pension Protection Act Zone Status Green Green  
FIP/RP Status Pending/Implemented No    
Contributions $ 14 $ 4 $ 4
Surcharge Imposed No    
Multiemployer Plan, Pension, Significant, Accumulated Benefit Obligation   5,748  
Multiemployer Plan, Pension, Significant, Plan Asset   $ 5,372  
Multiemployer Plan, Pension, Significant, Funded Status Percentage   0.93  
Steelworkers Pension Trust | ArcelorMittal USA and AK Steel [Member]      
Multiemployer Plan [Line Items]      
Multiemployer Plan, Pension, Significant, Contribution, Percentage   0.30 0.30
Steelworkers Pension Trust | Other Companies      
Multiemployer Plan [Line Items]      
Multiemployer Plan, Pension, Significant, Contribution, Percentage   0.05 0.05
Steelworkers Pension Trust | Minimum [Member]      
Multiemployer Plan [Line Items]      
Expiration Date of Collective Bargaining Agreement Jan. 22, 2021    
Steelworkers Pension Trust | Maximum [Member]      
Multiemployer Plan [Line Items]      
Expiration Date of Collective Bargaining Agreement Oct. 01, 2022    
IAM National Pension Fund's National Pension Plan      
Multiemployer Plan [Line Items]      
Pension Plan EIN 516031295    
Pension Plan Number 002    
Pension Protection Act Zone Status Red Green  
FIP/RP Status Pending/Implemented Implemented    
Contributions $ 16 $ 0 $ 0
Surcharge Imposed Yes    
IAM National Pension Fund's National Pension Plan | Minimum [Member]      
Multiemployer Plan [Line Items]      
Expiration Date of Collective Bargaining Agreement May 31, 2022    
IAM National Pension Fund's National Pension Plan | Maximum [Member]      
Multiemployer Plan [Line Items]      
Expiration Date of Collective Bargaining Agreement May 15, 2023    
American Maritime Officers Plan      
Multiemployer Plan [Line Items]      
Pension Plan EIN 131936709    
Pension Plan Number 001    
Pension Protection Act Zone Status Green Green  
FIP/RP Status Pending/Implemented No    
Contributions $ 0 $ 0 $ 0
Surcharge Imposed No    
Expiration Date of Collective Bargaining Agreement Jul. 31, 2021