v3.26.3
Document and Entity Information - shares
 9 Months Ended
Sep. 30, 2026
Nov. 12, 2026
Document and Entity Information    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Sep. 30, 2026  
Document Transition Report false  
Entity Registrant Name Concord Acquisition Corp II  
Entity Incorporation, State or Country Code DE  
Entity File Number 001-40773  
Entity Tax Identification Number 86-2171101  
Entity Address, Address Line One 477 Madison Avenue  
Entity Address, City or Town New York  
Entity Address State Or Province NY  
Entity Address, Postal Zip Code 10022  
City Area Code 212  
Local Phone Number 883-4330  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Shell Company true  
Entity Central Index Key 0001851959  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Units, each consisting of one share of Class A common stock and one-third of one redeemable warrant    
Document and Entity Information    
Title of 12(b) Security Units, each consisting of one share of Class A common stock and one-third of one redeemable warrant  
Trading Symbol CNDAU  
Class A common stock, par value $0.0001 per share    
Document and Entity Information    
Title of 12(b) Security Class A common stock, par value $0.0001 per share  
Trading Symbol CNDA  
Entity Common Stock, Shares Outstanding   8,550
Redeemable warrants, each whole warrant exercisable for one share of Class A common stock at an exercise price of $11.50    
Document and Entity Information    
Title of 12(b) Security Redeemable warrants, each whole warrant exercisable for one share of Class A common stock at an exercise price of $11.50  
Trading Symbol CNDAW  
Class B common stock    
Document and Entity Information    
Entity Common Stock, Shares Outstanding   7,002,438