Cover	6 Months Ended
	Jun. 30, 2020 shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
Document Transition Report	false
Entity File Number	001-15185
Entity Registrant Name	First Horizon National 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 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)	312,358,668
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0000036966
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false
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
Series A Preferred Stock
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 Preferred Stock
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 Preferred Stock
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 Preferred Stock
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 Preferred Stock
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