v3.26.1
Cover - shares
 6 Months Ended
Jun. 30, 2026
Aug. 10, 2026
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Amendment Flag false  
Document Period End Date Jun. 30, 2026  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Entity Registrant Name KEYSTONE ACQUISITION CORP.  
Entity Central Index Key 0002102771  
Entity File Number 001-43320  
Entity Tax Identification Number 00-0000000  
Entity Incorporation, State or Country Code E9  
Current Fiscal Year End Date --12-31  
Entity Address, Address Line One 142 West 57th Street  
Entity Address, Address Line Two 11th Floor  
Entity Address, City or Town New York  
Entity Address, State or Province NY  
Entity Address, Postal Zip Code 10019  
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  
City Area Code (408)  
Local Phone Number 482-7532  
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   9,583,333
Units, each consisting of one Class A ordinary share, $0.0001 par value, and one-half of one redeemable warrant    
Document Information [Line Items]    
Title of 12(b) Security Units, each consisting of one Class A ordinary share, $0.0001 par value, and one-half of one redeemable warrant  
Trading Symbol KEYYU  
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 KEYY  
Security Exchange Name NASDAQ  
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 Warrants, each whole warrant exercisable for one Class A ordinary share at an exercise price of $11.50 per share  
Trading Symbol KEYYW  
Security Exchange Name NASDAQ