v3.26.1
Cover - shares
 6 Months Ended
Jun. 30, 2026
Aug. 07, 2026
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Entity Interactive Data Current Yes  
Amendment Flag false  
Document Period End Date Jun. 30, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Entity Registrant Name Alussa Energy Acquisition Corp. II  
Entity Central Index Key 0002041493  
Entity File Number 001-42953  
Entity Incorporation, State or Country Code E9  
Entity Tax Identification Number 00-0000000  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Shell Company true  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Address, Address Line One 1001 S Capital of Texas Hwy  
Entity Address, Address Line Two Building L, Suite 250  
Entity Address, City or Town Austin  
Entity Address, State or Province TX  
City Area Code (512)  
Local Phone Number 904-0200  
Entity Address, Postal Zip Code 78746  
Class A Ordinary Shares    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   28,750,000
Class B Ordinary Shares    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   7,187,500
Units, each consisting of one Class A ordinary share and one-third of one redeemable warrant    
Document Information [Line Items]    
Title of 12(b) Security Units, each consisting of one Class A ordinary share and one-third of one redeemable warrant  
Trading Symbol ALUB U  
Security Exchange Name NYSE  
Class A ordinary shares, par value $0.0001 per share    
Document Information [Line Items]    
Title of 12(b) Security Class A ordinary shares, par value $0.0001 per share  
Trading Symbol ALUB  
Security Exchange Name NYSE  
Redeemable warrants, each whole warrant exercisable for one Class A ordinary share at an exercise price of $11.50    
Document Information [Line Items]    
Title of 12(b) Security Redeemable warrants, each whole warrant exercisable for one Class A ordinary share at an exercise price of $11.50  
Trading Symbol ALUB WS  
Security Exchange Name NYSE