Cover - shares	3 Months Ended
	Sep. 30, 2024	Dec. 09, 2024
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	Sep. 30, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Entity Information [Line Items]
Entity Registrant Name	Bleichroeder Acquisition Corp. I
Entity Central Index Key	0002028707
Entity File Number	001-42392
Entity Tax Identification Number	98-1797826
Entity Incorporation, State or Country Code	E9
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	No
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 Incorporation, Date of Incorporation	Jun. 24, 2024
Entity Contact Personnel [Line Items]
Entity Address, Address Line One	1345 Avenue of the America
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
Entity Phone Fax Numbers [Line Items]
City Area Code	(212)
Local Phone Number	984-3835
Units, each consisting of one Class A ordinary share and one right
Entity Listings [Line Items]
Title of 12(b) Security	Units, each consisting of one Class A ordinary share and one right
Trading Symbol	BACQU
Security Exchange Name	NASDAQ
Class A ordinary shares, par value $0.0001 per share
Entity Listings [Line Items]
Title of 12(b) Security	Class A ordinary shares, par value $0.0001 per share
Trading Symbol	BACQ
Security Exchange Name	NASDAQ
Rights, each right entitling the holder to receive one-tenth (1/10) of one Class A ordinary share
Entity Listings [Line Items]
Title of 12(b) Security	Rights, each right entitling the holder to receive one-tenth (1/10) of one Class A ordinary share
Trading Symbol	BACQR
Security Exchange Name	NASDAQ
Class A Ordinary Shares
Entity Listings [Line Items]
Entity Common Stock, Shares Outstanding		25,425,000
Class B Ordinary Shares
Entity Listings [Line Items]
Entity Common Stock, Shares Outstanding		8,333,333