v3.26.3
BUSINESS SEGMENTS - Schedule of Financial Information for Segments of FNB (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Segment Reporting [Line Items]          
Interest income $ 596.0 $ 596.0 $ 1,743.0 $ 1,738.0  
Interest expense 220.0 237.0 642.0 708.0  
Net Interest Income 376.0 359.0 1,101.0 1,030.0  
Provision for Credit Losses 19.0 24.0 59.5 67.1  
Non-interest income:          
Service charges 24.0 23.0 71.0 68.0  
Interchange and card transaction fees 13.0 13.0 39.0 39.0  
Trust services 12.0 12.0 37.0 36.0  
Insurance commissions and fees 5.0 5.0 17.0 16.0  
Securities commissions and fees 9.0 9.0 27.0 27.0  
Capital markets income 7.0 8.0 22.0 20.0  
Mortgage banking operations 6.0 9.0 18.0 22.0  
Other 17.0 19.0 50.0 49.0  
Total Non-Interest Income 93.0 98.0 281.0 277.0  
Non-interest expense:          
Salaries and employee benefits 133.0 131.0 404.0 396.0  
Other 124.0 112.0 364.0 340.0  
Total Non-Interest Expense 257.0 243.0 768.0 736.0  
Income tax expense (benefit) 40.0 40.0 116.0 107.0  
Net Income 153.0 150.0 439.0 397.0  
Total assets 52,053.0 49,889.0 52,053.0 49,889.0 $ 50,229.0
Total Loans and Leases 36,537.0 [1] 34,957.0 36,537.0 [1] 34,957.0 34,777.0 [1]
Total deposits 39,550.0 38,441.0 39,550.0 38,441.0 $ 38,759.0
Market value of assets under administration 15,207.0 14,885.0 15,207.0 14,885.0  
Operating Segments | Community Banking          
Segment Reporting [Line Items]          
Interest income 594.0 595.0 1,738.0 1,734.0  
Interest expense 212.0 225.0 619.0 667.0  
Net Interest Income 382.0 370.0 1,119.0 1,067.0  
Provision for Credit Losses 19.0 24.0 59.0 67.0  
Non-interest income:          
Service charges 24.0 23.0 71.0 68.0  
Interchange and card transaction fees 13.0 13.0 39.0 39.0  
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 17.0 16.0  
Mortgage banking operations 6.0 9.0 18.0 22.0  
Other 19.0 22.0 56.0 57.0  
Total Non-Interest Income 68.0 73.0 201.0 202.0  
Non-interest expense:          
Salaries and employee benefits 117.0 117.0 356.0 352.0  
Other 113.0 102.0 332.0 306.0  
Total Non-Interest Expense 230.0 219.0 688.0 658.0  
Income tax expense (benefit) 42.0 42.0 122.0 116.0  
Net Income 159.0 158.0 451.0 428.0  
Total assets 51,706.0 49,547.0 51,706.0 49,547.0  
Total Loans and Leases 36,487.0 34,911.0 36,487.0 34,911.0  
Total deposits 39,883.0 38,894.0 39,883.0 38,894.0  
Market value of assets under administration 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 12.0 37.0 36.0  
Insurance commissions and fees 0.0 0.0 0.0 0.0  
Securities commissions and fees 9.0 9.0 27.0 27.0  
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 21.0 64.0 63.0  
Non-interest expense:          
Salaries and employee benefits 11.0 11.0 34.0 32.0  
Other 2.0 3.0 7.0 10.0  
Total Non-Interest Expense 13.0 14.0 41.0 42.0  
Income tax expense (benefit) 1.0 2.0 5.0 5.0  
Net Income 7.0 5.0 18.0 16.0  
Total assets 51.0 47.0 51.0 47.0  
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 15,207.0 14,885.0 15,207.0 14,885.0  
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 5.0 5.0 17.0 16.0  
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 5.0 5.0 17.0 16.0  
Non-interest expense:          
Salaries and employee benefits 4.0 3.0 12.0 11.0  
Other 2.0 2.0 4.0 4.0  
Total Non-Interest Expense 6.0 5.0 16.0 15.0  
Income tax expense (benefit) 0.0 0.0 0.0 0.0  
Net Income (1.0) 0.0 1.0 1.0  
Total assets 40.0 31.0 40.0 31.0  
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 0.0 0.0 0.0 0.0  
Parent and Other          
Segment Reporting [Line Items]          
Interest income 2.0 1.0 5.0 4.0  
Interest expense 8.0 12.0 23.0 41.0  
Net Interest Income (6.0) (11.0) (18.0) (37.0)  
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 1.0 2.0 5.0 4.0  
Mortgage banking operations 0.0 0.0 0.0 0.0  
Other (2.0) (3.0) (6.0) (8.0)  
Total Non-Interest Income (1.0) (1.0) (1.0) (4.0)  
Non-interest expense:          
Salaries and employee benefits 1.0 0.0 2.0 1.0  
Other 7.0 5.0 21.0 20.0  
Total Non-Interest Expense 8.0 5.0 23.0 21.0  
Income tax expense (benefit) (3.0) (4.0) (11.0) (14.0)  
Net Income (12.0) (13.0) (31.0) (48.0)  
Total assets 256.0 264.0 256.0 264.0  
Total Loans and Leases 50.0 46.0 50.0 46.0  
Total deposits (333.0) (453.0) (333.0) (453.0)  
Market value of assets under administration $ 0.0 $ 0.0 $ 0.0 $ 0.0  
[1] Amount represents loans for which we have elected the fair value option. See Note 19.