Cover - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2020	Jan. 29, 2021	Jun. 30, 2020
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-15185
Entity Registrant Name	FIRST HORIZON CORPORATION
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			$ 3.0
Entity Common Stock, Shares Outstanding		555,468,634
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 27, 2021: Part III of this Report
Entity Central Index Key	0000036966
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Common Class A
Entity Information [Line Items]
Title of 12(b) Security	$.625 Par Value Common Capital Stock
Trading Symbol	FHN
Security Exchange Name	NYSE
Series A
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 A
Trading Symbol	FHN PR A
Security Exchange Name	NYSE
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
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
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
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