Acquisitions and Divestitures (Narrative) (Details)	9 Months Ended
	Oct. 02, 2015 USD ($) shares	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	[1]	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 191,307,000	$ 191,307,000		$ 145,932,000	$ 145,932,000
Trustatlantic Financial Corporation
Business Acquisition [Line Items]
Acquisition date	Oct. 02, 2015
Business Acquisition, Name of Acquired Entity	TrustAtlantic Financial Corporation
Business Acquisition, Description of Acquired Entity	Prior to the acquisition TAF and TAB were headquartered in Raleigh, North Carolina, where TAB had five branches located in the communities of Raleigh, Cary and Greenville.
Number of common shares issued in acquisition | shares	5,093,657
Number Of Bank Branches	5
As Recorded by FHN | Trustatlantic Financial Corporation
Business Acquisition [Line Items]
Cash payment to acquire business, gross	$ 23,900,000
Total transaction value	96,700,000
Assets acquired	400,000,000
Loans acquired	281,900,000
Deposits assumed	344,000,000
Goodwill	$ 45,400,000

[1] The increase in goodwill was related to the TAF acquisition in fourth quarter 2015.