| Cover - USD ($) $ in Billions | 12 Months Ended | ||
| Dec. 31, 2021 | Jan. 31, 2022 | Jun. 30, 2021 | |
| Entity Information [Line Items] | |||
| Document Type | 10-K/A | ||
| Document Annual Report | true | ||
| Document Period End Date | Dec. 31, 2021 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Document Transition Report | false | ||
| Entity File Number | 001-15185 | ||
| Entity Registrant Name | FIRST HORIZON CORP | ||
| Entity Incorporation, State or Country Code | TN | ||
| Entity Tax Identification Number | 62-0803242 | ||
| Entity Address, Address Line One | 165 Madison Avenue | ||
| Entity Address, City or Town | Memphis, | ||
| Entity Address, State or Province | TN | ||
| Entity Address, Postal Zip Code | 38103 | ||
| City Area Code | 901 | ||
| Local Phone Number | 523-4444 | ||
| 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 | ||
| Entity Shell Company | false | ||
| Entity Public Float | $ 9.4 | ||
| Entity Common Stock, Shares Outstanding (in shares) | 533,633,668 | ||
| Documents Incorporated by Reference | Portions of the Proxy Statement to be furnished to shareholders in connection with the Annual Meeting of shareholders scheduled for April 26, 2022: Part III of this Report | ||
| Auditor Name | KPMG LLP | ||
| Auditor Location | Memphis, TN | ||
| Auditor Firm ID | 185 | ||
| Entity Central Index Key | 0000036966 | ||
| Document Fiscal Year Focus | 2021 | ||
| Document Fiscal Period Focus | FY | ||
| Amendment Flag | false | ||
| $.625 Par Value Common Capital Stock | |||
| Entity Information [Line Items] | |||
| Title of 12(b) Security | $.625 Par Value Common Capital Stock | ||
| Trading Symbol | FHN | ||
| Security Exchange Name | NYSE | ||
| Depositary Shares, each representing a 1/400th interest in a share of Non-Cumulative Perpetual Preferred Stock, Series B | |||
| Entity Information [Line Items] | |||
| Title of 12(b) Security | Depositary Shares, each representing a 1/400th interest ina share of Non-Cumulative Perpetual Preferred Stock, Series B | ||
| Trading Symbol | FHN PR B | ||
| Security Exchange Name | NYSE | ||
| Depositary Shares, each representing a 1/400th interest in a share of Non-Cumulative Perpetual Preferred Stock, Series C | |||
| Entity Information [Line Items] | |||
| Title of 12(b) Security | Depositary Shares, each representing a 1/400th interest ina share of Non-Cumulative Perpetual Preferred Stock, Series C | ||
| Trading Symbol | FHN PR C | ||
| Security Exchange Name | NYSE | ||
| Depositary Shares, each representing a 1/400th interest in a share of Non-Cumulative Perpetual Preferred Stock, Series D | |||
| Entity Information [Line Items] | |||
| Title of 12(b) Security | Depositary Shares, each representing a 1/400th interest ina share of Non-Cumulative Perpetual Preferred Stock, Series D | ||
| Trading Symbol | FHN PR D | ||
| Security Exchange Name | NYSE | ||
| Depositary Shares, each representing a 1/4,000th interest in a share of Non-Cumulative Perpetual Preferred Stock, Series E | |||
| Entity Information [Line Items] | |||
| Title of 12(b) Security | Depositary Shares, each representing a 1/4,000th interest ina share of Non-Cumulative Perpetual Preferred Stock, Series E | ||
| Trading Symbol | FHN PR E | ||
| Security Exchange Name | NYSE | ||
| Depositary Shares, each representing a 1/4,000th interest in a share of Non-Cumulative Perpetual Preferred Stock, Series F | |||
| Entity Information [Line Items] | |||
| Title of 12(b) Security | Depositary Shares, each representing a 1/4,000th interest ina share of Non-Cumulative Perpetual Preferred Stock, Series F | ||
| Trading Symbol | FHN PR F | ||
| Security Exchange Name | NYSE |
