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COVER - USD ($)
$ in Billions
 12 Months Ended
Dec. 31, 2024
Jun. 30, 2024
Dec. 31, 2023
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2024    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-35931    
Registrant Name Constellium SE    
Entity Incorporation, State or Country Code I0    
Entity Address, Address Line One 300 East Lombard Street, Suite 1710    
Entity Address, City or Town Baltimore,    
Entity Address, State or Province MD    
Entity Address, Postal Zip Code 21202    
City Area Code (443)    
Local Phone Number 420-7861    
Title of 12(b) Security Ordinary Shares    
Trading Symbol CSTM    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
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    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float   $ 2.7  
Common stock, shares issued (in shares) 146,819,884   146,819,884
Entity common stock, shares outstanding (in shares) 143,523,308    
Amendment Flag false    
Document Fiscal Year Focus 2024    
Document Fiscal Period Focus FY    
Central Index Key 0001563411