v3.26.1
BUSINESS SEGMENTS - Schedule of Financial Information for Segments of FNB (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Segment Reporting [Line Items]          
Interest income $ 578.0 $ 583.0 $ 1,147.0 $ 1,142.0  
Interest expense 212.0 235.0 422.0 471.0  
Net Interest Income 366.0 348.0 725.0 671.0  
Provision for Credit Losses 22.0 26.0 39.8 43.1  
Non-interest income:          
Service charges 24.0 23.0 47.0 45.0  
Interchange and card transaction fees 13.0 14.0 26.0 26.0  
Trust services 12.0 11.0 25.0 24.0  
Insurance commissions and fees 6.0 5.0 12.0 11.0  
Securities commissions and fees 9.0 9.0 18.0 18.0  
Capital markets income 8.0 7.0 15.0 12.0  
Mortgage banking operations 6.0 6.0 12.0 13.0  
Other 19.0 16.0 33.0 30.0  
Total Non-Interest Income 97.0 91.0 188.0 179.0  
Non-interest expense:          
Salaries and employee benefits 135.0 130.0 271.0 265.0  
Other 118.0 117.0 240.0 228.0  
Total Non-Interest Expense 253.0 247.0 511.0 493.0  
Income tax expense (benefit) 39.0 36.0 76.0 67.0  
Net Income 149.0 130.0 286.0 247.0  
Total assets 50,999.0 49,725.0 50,999.0 49,725.0 $ 50,229.0
Total Loans and Leases 35,769.0 [1] 34,679.0 35,769.0 [1] 34,679.0 34,777.0 [1]
Total deposits 38,679.0 37,748.0 38,679.0 37,748.0 $ 38,759.0
Market value of assets under administration - FNBIA, FNTC and FNIS 15,504.0 14,425.0 15,504.0 14,425.0  
Operating Segments | Community Banking          
Segment Reporting [Line Items]          
Interest income 577.0 581.0 1,144.0 1,139.0  
Interest expense 205.0 221.0 407.0 442.0  
Net Interest Income 372.0 360.0 737.0 697.0  
Provision for Credit Losses 22.0 26.0 40.0 43.0  
Non-interest income:          
Service charges 24.0 23.0 47.0 45.0  
Interchange and card transaction fees 13.0 14.0 26.0 26.0  
Trust services 0.0 0.0 0.0 0.0  
Insurance commissions and fees 0.0 0.0 0.0 0.0  
Securities commissions and fees 0.0 0.0 0.0 0.0  
Capital markets income 6.0 6.0 11.0 10.0  
Mortgage banking operations 6.0 6.0 12.0 13.0  
Other 20.0 17.0 37.0 35.0  
Total Non-Interest Income 69.0 66.0 133.0 129.0  
Non-interest expense:          
Salaries and employee benefits 119.0 114.0 239.0 235.0  
Other 107.0 103.0 219.0 204.0  
Total Non-Interest Expense 226.0 217.0 458.0 439.0  
Income tax expense (benefit) 41.0 40.0 80.0 74.0  
Net Income 152.0 143.0 292.0 270.0  
Total assets 50,660.0 49,380.0 50,660.0 49,380.0  
Total Loans and Leases 35,718.0 34,634.0 35,718.0 34,634.0  
Total deposits 39,000.0 38,552.0 39,000.0 38,552.0  
Market value of assets under administration - FNBIA, FNTC and FNIS 0.0 0.0 0.0 0.0  
Operating Segments | Wealth Management          
Segment Reporting [Line Items]          
Interest income 0.0 0.0 0.0 0.0  
Interest expense 0.0 0.0 0.0 0.0  
Net Interest Income 0.0 0.0 0.0 0.0  
Provision for Credit Losses 0.0 0.0 0.0 0.0  
Non-interest income:          
Service charges 0.0 0.0 0.0 0.0  
Interchange and card transaction fees 0.0 0.0 0.0 0.0  
Trust services 12.0 11.0 25.0 24.0  
Insurance commissions and fees 0.0 0.0 0.0 0.0  
Securities commissions and fees 9.0 9.0 18.0 18.0  
Capital markets income 0.0 0.0 0.0 0.0  
Mortgage banking operations 0.0 0.0 0.0 0.0  
Other 0.0 0.0 0.0 0.0  
Total Non-Interest Income 21.0 20.0 43.0 42.0  
Non-interest expense:          
Salaries and employee benefits 12.0 11.0 23.0 21.0  
Other 2.0 3.0 5.0 7.0  
Total Non-Interest Expense 14.0 14.0 28.0 28.0  
Income tax expense (benefit) 2.0 1.0 4.0 3.0  
Net Income 5.0 5.0 11.0 11.0  
Total assets 52.0 45.0 52.0 45.0  
Total Loans and Leases 0.0 0.0 0.0 0.0  
Total deposits 0.0 0.0 0.0 0.0  
Market value of assets under administration - FNBIA, FNTC and FNIS 15,504.0 14,425.0 15,504.0 14,425.0  
Operating Segments | Insurance          
Segment Reporting [Line Items]          
Interest income 0.0 0.0 0.0 0.0  
Interest expense 0.0 0.0 0.0 0.0  
Net Interest Income 0.0 0.0 0.0 0.0  
Provision for Credit Losses 0.0 0.0 0.0 0.0  
Non-interest income:          
Service charges 0.0 0.0 0.0 0.0  
Interchange and card transaction fees 0.0 0.0 0.0 0.0  
Trust services 0.0 0.0 0.0 0.0  
Insurance commissions and fees 6.0 5.0 12.0 11.0  
Securities commissions and fees 0.0 0.0 0.0 0.0  
Capital markets income 0.0 0.0 0.0 0.0  
Mortgage banking operations 0.0 0.0 0.0 0.0  
Other 0.0 0.0 0.0 0.0  
Total Non-Interest Income 6.0 5.0 12.0 11.0  
Non-interest expense:          
Salaries and employee benefits 4.0 4.0 8.0 8.0  
Other 1.0 1.0 2.0 2.0  
Total Non-Interest Expense 5.0 5.0 10.0 10.0  
Income tax expense (benefit) 0.0 0.0 0.0 0.0  
Net Income 1.0 0.0 2.0 1.0  
Total assets 34.0 35.0 34.0 35.0  
Total Loans and Leases 0.0 0.0 0.0 0.0  
Total deposits 0.0 0.0 0.0 0.0  
Market value of assets under administration - FNBIA, FNTC and FNIS 0.0 0.0 0.0 0.0  
Parent and Other          
Segment Reporting [Line Items]          
Interest income 1.0 2.0 3.0 3.0  
Interest expense 7.0 14.0 15.0 29.0  
Net Interest Income (6.0) (12.0) (12.0) (26.0)  
Provision for Credit Losses 0.0 0.0 0.0 0.0  
Non-interest income:          
Service charges 0.0 0.0 0.0 0.0  
Interchange and card transaction fees 0.0 0.0 0.0 0.0  
Trust services 0.0 0.0 0.0 0.0  
Insurance commissions and fees 0.0 0.0 0.0 0.0  
Securities commissions and fees 0.0 0.0 0.0 0.0  
Capital markets income 2.0 1.0 4.0 2.0  
Mortgage banking operations 0.0 0.0 0.0 0.0  
Other (1.0) (1.0) (4.0) (5.0)  
Total Non-Interest Income 1.0 0.0 0.0 (3.0)  
Non-interest expense:          
Salaries and employee benefits 0.0 1.0 1.0 1.0  
Other 8.0 10.0 14.0 15.0  
Total Non-Interest Expense 8.0 11.0 15.0 16.0  
Income tax expense (benefit) (4.0) (5.0) (8.0) (10.0)  
Net Income (9.0) (18.0) (19.0) (35.0)  
Total assets 253.0 265.0 253.0 265.0  
Total Loans and Leases 51.0 45.0 51.0 45.0  
Total deposits (321.0) (804.0) (321.0) (804.0)  
Market value of assets under administration - FNBIA, FNTC and FNIS $ 0.0 $ 0.0 $ 0.0 $ 0.0  
[1] Amount represents loans for which we have elected the fair value option. See Note 19.