Document And Entity Information	9 Months Ended
	Sep. 30, 2018 shares
Document And Entity Information [Abstract]
Entity Registrant Name	FIRST HORIZON NATIONAL CORP
Entity Central Index Key	0000036966
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding (in shares)	323,942,816
Trading Symbol	FHN
Entity Emerging Growth Company	false
Entity Small Business	false