v3.26.1
Cover - USD ($)
 12 Months Ended
Dec. 31, 2025
Mar. 31, 2026
Jun. 30, 2025
Document Type 10-K    
Amendment Flag false    
Document Annual Report true    
Document Transition Report false    
Document Period End Date Dec. 31, 2025    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2025    
Current Fiscal Year End Date --12-31    
Entity File Number 001-42622    
Entity Registrant Name Copley Acquisition Corp    
Entity Central Index Key 0002045473    
Entity Tax Identification Number 00-0000000    
Entity Incorporation, State or Country Code E9    
Entity Address, Address Line One Suite 4005-4006, 40/F    
Entity Address, Address Line Two One Exchange Square    
Entity Address, Address Line Three 8 Connaught Place    
Entity Address, City or Town Central    
Entity Address, Country HK    
Entity Address, Postal Zip Code 00000    
City Area Code 852    
Local Phone Number 2861 3335    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
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    
Elected Not To Use the Extended Transition Period false    
Entity Shell Company true    
Entity Public Float     $ 175,096,125
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction [Flag] false    
Auditor Name WithumSmith+Brown, PC    
Auditor Location New York    
Auditor Firm ID 100    
Units, each consisting of one Class A ordinary share and one-half of one redeemable warrant      
Title of 12(b) Security Units, each consisting of one Class A ordinary share and one-half of one warrant    
Trading Symbol COPLU    
Security Exchange Name NYSE    
Class A ordinary shares, par value $0.0001 per share      
Title of 12(b) Security Class A ordinary shares, par value $0.0001 per share    
Trading Symbol COPL    
Security Exchange Name NYSE    
Warrants, each whole warrant entitles the holder thereof to purchase one Class A ordinary share at a price of $11.50 per share      
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 COPLW    
Security Exchange Name NYSE    
Common Classs A [Member]      
Entity Common Stock, Shares Outstanding   17,978,393  
Commons Class B [Member]      
Entity Common Stock, Shares Outstanding   5,750,000