v3.26.1
Cover - shares
 6 Months Ended
Jun. 30, 2026
Aug. 14, 2026
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Entity Registrant Name Bleichroeder Acquisition Corp. III  
Document Period End Date Jun. 30, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Current Fiscal Year End Date --12-31  
Entity Central Index Key 0002128045  
Entity File Number 001-43387  
Amendment Flag false  
Entity Incorporation, State or Country Code E9  
Entity Tax Identification Number 98-1931116  
Entity Address, Address Line One 1345 Avenue of the Americas  
Entity Address, Address Line Two Fl 47  
Entity Address, City or Town New York  
Entity Address, State or Province NY  
Entity Address, Postal Zip Code 10105  
City Area Code 212  
Local Phone Number 984-3835  
Entity Current Reporting Status No  
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  
Units, each consisting of one Class A ordinary share and one-fourth of one redeemable warrant    
Document Information [Line Items]    
Title of 12(b) Security Units, each consisting of one Class A ordinary share and one-fourth of one redeemable warrant  
Trading Symbol BCCQU  
Security Exchange Name NASDAQ  
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 BCCQ  
Security Exchange Name NASDAQ  
Redeemable warrants, each whole warrant exercisable for one Class A ordinary share at an exercise price of $11.50 per share    
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 per share  
Trading Symbol BCCQW  
Security Exchange Name NASDAQ  
Class A Ordinary Shares    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   34,500,000
Class B Ordinary Shares    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   11,500,000