v3.25.4
Cover - USD ($)
 12 Months Ended
Dec. 31, 2025
Mar. 06, 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    
Entity Registrant Name NEWBURY STREET II ACQUISITION CORP    
Entity Central Index Key 0002028027    
Entity File Number 001-42391    
Entity Tax Identification Number 98-1797287    
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     $ 180,217,774
Entity Address, Address Line One 121 High Street    
Entity Address, Address Line Two Floor 3    
Entity Address, City or Town Boston    
Entity Address, State or Province MA    
Entity Address, Postal Zip Code 02110    
City Area Code (617)    
Local Phone Number 334-2805    
Units, each consisting of one Class A Ordinary Share 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 and one-half of one redeemable Warrant    
Trading Symbol NTWOU    
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 NTWO    
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 NTWOW    
Security Exchange Name NASDAQ    
Class A Ordinary Shares      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   17,998,375  
Class B Ordinary Shares      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   6,118,000