Term Borrowings - Schedule of Information Pertaining to Term Borrowings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Term borrowings	$ 1,195	$ 1,150
Junior Subordinated Debt
Debt Instrument [Line Items]
Debt term	30 years
Junior Subordinated Debt | First Horizon Corporation
Debt Instrument [Line Items]
Basis spread on variable rate	0.26161%
Maturity date – May 1, 2030 - 5.75% | Senior Notes | First Horizon Bank
Debt Instrument [Line Items]
Term borrowings	$ 448	$ 448
Stated interest rate	5.75%	5.75%
0.00% on December 31, 2024 and 5.95% on December 31, 2023 | Collateralized By Loans | First Horizon Bank
Debt Instrument [Line Items]
Term borrowings	$ 88	$ 88
Effective interest rate	4.92%	5.95%
Other collateralized borrowings - SBA loans | Collateralized By Loans | First Horizon Bank
Debt Instrument [Line Items]
Term borrowings	$ 37	$ 3
Debt, weighted average interest rate	7.08%	4.81%
Other collateralized borrowings - SBA loans | Collateralized By Loans | First Horizon Bank | Minimum
Debt Instrument [Line Items]
Debt term	1 year
Other collateralized borrowings - SBA loans | Collateralized By Loans | First Horizon Bank | Maximum
Debt Instrument [Line Items]
Debt term	25 years
Maturity date – May 26, 2025 - 4.00% | Senior Notes | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 350	$ 349
Stated interest rate	4.00%	4.00%
Maturity date - June 28, 2035 - 6.30% on December 31, 2024 and 7.33% on December 31, 2023 | Junior Subordinated Debt | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 3	$ 3
Stated interest rate	6.30%	7.33%
Maturity date - December 15, 2035 - 5.99% on December 31, 2024 and 7.02% on December 31, 2023 | Junior Subordinated Debt | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 18	$ 18
Stated interest rate	5.99%	7.02%
Maturity date - March 15, 2036 - 6.02% on December 31, 2024 and 7.05% on December 31, 2023 | Junior Subordinated Debt | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 9	$ 9
Stated interest rate	6.02%	7.05%
Maturity date - March 15, 2036 - 6.16% on December 31, 2024 and 7.19% on December 31, 2023 | Junior Subordinated Debt | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 12	$ 12
Stated interest rate	6.16%	7.19%
Maturity date - June 30, 2036 - 5.91% on December 31, 2024 and 6.91% on December 31, 2023 | Junior Subordinated Debt | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 28	$ 28
Stated interest rate	5.91%	6.91%
Maturity date - July 7, 2036 - 6.47% on December 31, 2024 and 7.21% on December 31, 2023 | Junior Subordinated Debt | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 19	$ 19
Stated interest rate	6.47%	7.21%
Maturity date - June 15, 2037 - 6.27% on December 31, 2024 and 7.30% on December 31, 2023 | Junior Subordinated Debt | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 53	$ 52
Stated interest rate	6.27%	7.30%
Maturity date - September 6, 2037 - 6.14% on December 31, 2024 and 7.05% on December 31, 2023 | Junior Subordinated Debt | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 9	$ 9
Stated interest rate	6.14%	7.05%
Notes payable - New market tax credit investments; 16 to 35 year term, 0.93% to 4.75% on December 31, 2024; 7 to 35 year term, 0.93% to 4.95% on December 31, 2023 | Notes Payable, Other Payables | First Horizon Corporation
Debt Instrument [Line Items]
Term borrowings	$ 74	$ 65
Notes payable - New market tax credit investments; 16 to 35 year term, 0.93% to 4.75% on December 31, 2024; 7 to 35 year term, 0.93% to 4.95% on December 31, 2023 | Notes Payable, Other Payables | First Horizon Corporation | Minimum
Debt Instrument [Line Items]
Debt term	16 years	7 years
Debt, weighted average interest rate	0.93%	0.93%
Notes payable - New market tax credit investments; 16 to 35 year term, 0.93% to 4.75% on December 31, 2024; 7 to 35 year term, 0.93% to 4.95% on December 31, 2023 | Notes Payable, Other Payables | First Horizon Corporation | Maximum
Debt Instrument [Line Items]
Debt term	35 years	35 years
Debt, weighted average interest rate	4.75%	4.95%
Maturity date – March 31, 2031 – 9.50% | Cumulative Preferred Stock | FT Real Estate Securities Company, Inc.:
Debt Instrument [Line Items]
Term borrowings	$ 47	$ 47
Stated interest rate	9.50%	9.50%