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COVER PAGE - USD ($)
 12 Months Ended
Dec. 31, 2025
Jan. 31, 2026
Jun. 30, 2025
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-31940    
Entity Registrant Name FNB CORP/PA/    
Entity Incorporation, State or Country Code PA    
Entity Tax Identification Number 25-1255406    
Entity Address, Address Line One 626 Washington Place,    
Entity Address, City or Town Pittsburgh,    
Entity Address, State or Province PA    
Entity Address, Postal Zip Code 15219    
City Area Code 800    
Local Phone Number 555-5455    
Title of 12(b) Security Common Stock, par value $0.01 per share    
Trading Symbol FNB    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     $ 5,043,012,309
Entity Common Stock, Shares Outstanding   357,389,017  
Documents Incorporated by Reference
Portions of F.N.B. Corporation’s definitive proxy statement to be filed in connection with the 2026 Annual Meeting of Shareholders to be held on May 6, 2026 are incorporated by reference into Part III of this Annual Report on Form 10-K.
    
Amendment Flag false    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Entity Central Index Key 0000037808