v3.26.1
Cover - USD ($)
12 Months Ended
Dec. 31, 2025
Mar. 30, 2026
Jun. 30, 2025
Document Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Transition Report false    
Document Financial Statement Error Correction [Flag] false    
Entity Interactive Data Current Yes    
ICFR Auditor Attestation Flag false    
Amendment Flag false    
Document Period End Date Dec. 31, 2025    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Documents Incorporated by Reference [Text Block] None.    
Entity Registrant Name HELIX ACQUISITION CORP. III    
Entity Central Index Key 0002099656    
Entity File Number 001-43069    
Entity Tax Identification Number 98-1895727    
Entity Incorporation, State or Country Code E9    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
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 Public Float     $ 169,270,500
Entity Address, Address Line One Cormorant Asset Management    
Entity Address, Address Line Two LP200 Clarendon Street    
Entity Address, Address Line Three 52nd Floor    
Entity Address, City or Town Boston    
Entity Address, Country MA    
Entity Address, Postal Zip Code 02116    
City Area Code (857)    
Local Phone Number 702-0370    
Title of 12(b) Security Class A ordinary shares, par value $0.0001 per share    
Trading Symbol HLXC    
Security Exchange Name NASDAQ    
Class A Ordinary Shares      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   17,747,500  
Class B Ordinary Shares      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   4,312,500