| Document and Entity Information | Jan. 22, 2022 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | FNB CORP/PA/ |
| Amendment Flag | false |
| Entity Central Index Key | 0000037808 |
| Document Type | 8-K |
| Document Period End Date | Jan. 22, 2022 |
| Entity Incorporation State Country Code | PA |
| Entity File Number | 001-31940 |
| Entity Tax Identification Number | 25-1255406 |
| Entity Address, Address Line One | One North Shore Center |
| Entity Address, Address Line Two | 12 Federal Street |
| Entity Address, City or Town | Pittsburgh |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 15212 |
| City Area Code | (800) |
| Local Phone Number | 555-5455 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | FNB |
| Security Exchange Name | NYSE |
| Series E Preferred Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Depositary Shares each representing 1/40th interest in a share of Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series E |
| Trading Symbol | FNBPrE |
| Security Exchange Name | NYSE |
