Document And Entity Information	9 Months Ended
	Sep. 30, 2012
Document And Entity Information [Abstract]
Entity Registrant Name	FIRST HORIZON NATIONAL CORP
Entity Central Index Key	0000036966
Document Type	10-Q
Document Period End Date	Sep. 30, 2012
Amendment Flag	false
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	247,133,973