Cover - shares		3 Months Ended
	May 06, 2021	Mar. 31, 2021
Entity Information [Line Items]
Document Type		10-Q
Document Quarterly Report		true
Document Period End Date		Mar. 31, 2021
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 Current Reporting Status		Yes
Entity Interactive Data Current		Yes
Entity Filer Category		Large Accelerated Filer
Entity Small Business		false
Entity Emerging Growth Company		false
Entity Shell Company		false
Entity Common Stock, Shares Outstanding (in shares)		552,374,489
Entity Central Index Key		0000036966
Current Fiscal Year End Date		--12-31
Document Fiscal Year Focus		2021
Document Fiscal Period Focus		Q1
Amendment Flag		false
Entity Information, Former Legal or Registered Name		FIRST HORIZON NATIONAL CORP
$.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 1/4,000th interest in a share of Non-Cumulative Perpetual Preferred Stock, 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
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* | Subsequent Event
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