Term Borrowings - Schedule of Information Pertaining To Term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Debt Instrument [Line Items]
Term borrowings	$ 791,368		$ 1,170,963
Loans, net of unearned income	31,061,111	[1]	27,535,532	[1]	$ 27,658,929
Retail Real Estate Residential
Debt Instrument [Line Items]
Loans, net of unearned income			16,200
First Horizon Bank | Senior Notes | Maturity date – December 1, 2019 – 2.95%
Debt Instrument [Line Items]
Term borrowings	$ 0		$ 395,872
Stated interest rate	2.95%		2.95%
First Horizon Bank | Collateralized By Loans | 2.19% on December 31, 2019 and 3.09% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 80,908		$ 76,642
Effective interest rate	2.19%		3.09%
First Horizon Bank | Collateralized By Loans | Other collateralized borrowings - SBA loans
Debt Instrument [Line Items]
Term borrowings	$ 21,975		$ 16,607
Debt, weighted average interest rate	3.95%		3.95%
First Horizon National Corporation | Senior Notes | Maturity date – December 15, 2020 – 3.50%
Debt Instrument [Line Items]
Term borrowings	$ 497,656		$ 486,739
Stated interest rate	3.50%		3.50%
First Horizon National Corporation | Junior Subordinated Debt | Maturity date - June 28, 2035 - 3.57% on December 31, 2019 and 4.47% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 2,752		$ 2,730
Stated interest rate	3.57%		4.47%
First Horizon National Corporation | Junior Subordinated Debt | Maturity date - December 15, 2035 - 3.26% on December 31, 2019 and 4.16% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 17,642		$ 17,456
Stated interest rate	3.26%		4.16%
First Horizon National Corporation | Junior Subordinated Debt | Maturity date - March 15, 2036 - 3.29% on December 31, 2019 and 4.19% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 8,847		$ 8,757
Stated interest rate	3.29%		4.19%
First Horizon National Corporation | Junior Subordinated Debt | Maturity date - March 15, 2036 - 3.43% on December 31, 2019 and 4.33% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 11,692		$ 11,587
Stated interest rate	3.43%		4.33%
First Horizon National Corporation | Junior Subordinated Debt | Maturity date - June 30, 2036 - 3.28% on December 31, 2019 and 4.12% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 26,217		$ 25,931
Stated interest rate	3.28%		4.12%
First Horizon National Corporation | Junior Subordinated Debt | Maturity date - July 7, 2036 - 3.54% on December 31, 2019 and 3.99% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 17,964		$ 17,803
Stated interest rate	3.54%		3.99%
First Horizon National Corporation | Junior Subordinated Debt | Maturity date - June 15, 2037 - 3.54% on December 31, 2019 and 4.44% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 50,681		$ 50,278
Stated interest rate	3.54%		4.44%
First Horizon National Corporation | Junior Subordinated Debt | Maturity date - September 6, 2037 - 3.32% on December 31, 2019 and 4.17% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 8,798		$ 8,713
Stated interest rate	3.32%		4.17%
FT Real Estate Securities Company, Inc. | Cumulative Preferred Stock | Maturity date – March 31, 2031 – 9.50%
Debt Instrument [Line Items]
Term borrowings	$ 46,236		$ 46,168
Stated interest rate	9.50%		9.50%
First Horizon ABS Trusts | Collateralized By Loans | 2.66% on December 31, 2018
Debt Instrument [Line Items]
Term borrowings	$ 0		$ 2,981
Effective interest rate			2.66%
First Tennessee New Market Corporation Investments | Maturity date – August 08, 2036 – 2.38%
Debt Instrument [Line Items]
Term borrowings	$ 0		$ 2,699
Stated interest rate			2.38%
Minimum | First Horizon Bank | Collateralized By Loans | Other collateralized borrowings - SBA loans
Debt Instrument [Line Items]
Debt term	3 years
Maximum | First Horizon Bank | Collateralized By Loans | Other collateralized borrowings - SBA loans
Debt Instrument [Line Items]
Debt term	25 years

[1] December 31, 2019 and 2018 include $18.8 million and $28.6 million, respectively, of held-to-maturity consumer mortgage loans secured by residential real estate in process of foreclosure.