Term Borrowings - Schedule of Information Pertaining To Term Borrowings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Term borrowings	$ 1,150	$ 1,597
Junior Subordinated Debt
Debt Instrument [Line Items]
Debt term	30 years
First Horizon Bank | Senior Notes | Maturity date – May 1, 2030 - 5.75%
Debt Instrument [Line Items]
Term borrowings	$ 448	$ 448
Stated interest rate	5.75%	5.75%
First Horizon Bank | Collateralized By Loans | 0.50% on December 31, 2022 and 0.50% on December 31, 2021
Debt Instrument [Line Items]
Term borrowings	$ 88	$ 87
Effective interest rate	5.95%	5.07%
First Horizon Bank | Collateralized By Loans | Other collateralized borrowings - SBA loans
Debt Instrument [Line Items]
Term borrowings	$ 3	$ 3
Debt, weighted average interest rate	4.81%	5.13%
First Horizon Corporation | Senior Notes | Maturity date – May 26, 2023 - 3.55%
Debt Instrument [Line Items]
Term borrowings	$ 0	$ 450
Stated interest rate	3.55%	3.55%
First Horizon Corporation | Senior Notes | Maturity date – May 26, 2025 - 4.00%
Debt Instrument [Line Items]
Term borrowings	$ 349	$ 349
Stated interest rate	4.00%	4.00%
First Horizon Corporation | Junior Subordinated Debt | Maturity date - June 28, 2035 - 7.33% on December 31, 2023 and 6.45% on December 31, 2022
Debt Instrument [Line Items]
Term borrowings	$ 3	$ 3
Stated interest rate	7.33%	6.45%
First Horizon Corporation | Junior Subordinated Debt | Maturity date - December 15, 2035 - 7.02% on December 31, 2023 and 6.14% on December 31, 2022
Debt Instrument [Line Items]
Term borrowings	$ 18	$ 18
Stated interest rate	7.02%	6.14%
First Horizon Corporation | Junior Subordinated Debt | Maturity date - March 15, 2036 - 7.05% on December 31, 2023 and 6.17% on December 31, 2022
Debt Instrument [Line Items]
Term borrowings	$ 9	$ 9
Stated interest rate	7.05%	6.17%
First Horizon Corporation | Junior Subordinated Debt | Maturity date - March 15, 2036 - 7.19% on December 31, 2023 and 6.31% on December 31, 2022
Debt Instrument [Line Items]
Term borrowings	$ 12	$ 12
Stated interest rate	7.19%	6.31%
First Horizon Corporation | Junior Subordinated Debt | Maturity date - June 30, 2036 - 6.91% on December 31, 2023 and 6.05% on December 31, 2022
Debt Instrument [Line Items]
Term borrowings	$ 28	$ 27
Stated interest rate	6.91%	6.05%
First Horizon Corporation | Junior Subordinated Debt | Maturity date - July 7, 2036 - 7.21% on December 31, 2023 and 5.63% on December 31, 2022
Debt Instrument [Line Items]
Term borrowings	$ 19	$ 18
Stated interest rate	7.21%	5.63%
First Horizon Corporation | Junior Subordinated Debt | Maturity date - June 15, 2037 - 7.30% on December 31, 2023 and 6.42% on December 31, 2022
Debt Instrument [Line Items]
Term borrowings	$ 52	$ 52
Stated interest rate	7.30%	6.42%
First Horizon Corporation | Junior Subordinated Debt | Maturity date - September 6, 2037 - 7.05% on December 31, 2023 and 6.16% on December 31, 2022
Debt Instrument [Line Items]
Term borrowings	$ 9	$ 9
Stated interest rate	7.05%	6.16%
First Horizon Corporation | Notes Payable, Other Payables | New Market Tax Credit Investments
Debt Instrument [Line Items]
Term borrowings	$ 65	$ 66
FT Real Estate Securities Company, Inc. | Cumulative Preferred Stock | Maturity date – March 31, 2031 – 9.50%
Debt Instrument [Line Items]
Term borrowings	$ 47	$ 46
Stated interest rate	9.50%	9.50%
Minimum | First Horizon Bank | Collateralized By Loans | Other collateralized borrowings - SBA loans
Debt Instrument [Line Items]
Debt term	2 years
Minimum | First Horizon Corporation | Notes Payable, Other Payables | New Market Tax Credit Investments
Debt Instrument [Line Items]
Debt term	7 years
Debt, weighted average interest rate	0.93%
Maximum | First Horizon Bank | Collateralized By Loans | Other collateralized borrowings - SBA loans
Debt Instrument [Line Items]
Debt term	25 years
Maximum | First Horizon Corporation | Notes Payable, Other Payables | New Market Tax Credit Investments
Debt Instrument [Line Items]
Debt term	35 years
Debt, weighted average interest rate	4.95%