Regulatory Capital and Restrictions - Schedule of Actual Capital Amounts and Ratios (Details) $ in Millions	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
First Horizon Corporation
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital, Actual Amount	$ 9,862	$ 9,922
Total Capital, Actual Ratio	0.1387	0.1396
Tier 1 Capital, Actual Amount	$ 8,688	$ 8,825
Tier 1 Capital, Actual Ratio	0.1222	0.1242
Common Equity Tier 1 Capital, Actual Amount	$ 7,967	$ 8,104
Common Equity Tier 1 Capital, Actual Ratio	11.20%	11.40%
Leverage, Actual Amount	$ 8,688	$ 8,825
Leverage, Actual Ratio	0.1064	0.1069
Total Capital, Capital Adequacy purposes, Amount	$ 5,689	$ 5,686
Total Capital, Capital Adequacy Purposes, Ratio	0.0800	0.0800
Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 4,266	$ 4,264
Tier 1 Capital, Capital Adequacy Purposes, Ratio	0.0600	0.0600
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 3,200	$ 3,198
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Ratio	4.50%	4.50%
Leverage, Capital Adequacy Purposes, Amount	$ 3,266	$ 3,302
Leverage, Capital Adequacy Purposes, Ratio	0.0400	0.0400
First Horizon Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital, Actual Amount	$ 9,156	$ 9,303
Total Capital, Actual Ratio	0.1300	0.1317
Tier 1 Capital, Actual Amount	$ 8,129	$ 8,350
Tier 1 Capital, Actual Ratio	0.1154	0.1182
Common Equity Tier 1 Capital, Actual Amount	$ 7,834	$ 8,055
Common Equity Tier 1 Capital, Actual Ratio	11.12%	11.40%
Leverage, Actual Amount	$ 8,129	$ 8,350
Leverage, Actual Ratio	0.1006	0.1020
Total Capital, Capital Adequacy purposes, Amount	$ 5,633	$ 5,651
Total Capital, Capital Adequacy Purposes, Ratio	0.0800	0.0800
Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 4,225	$ 4,238
Tier 1 Capital, Capital Adequacy Purposes, Ratio	0.0600	0.0600
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 3,169	$ 3,179
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Ratio	4.50%	4.50%
Leverage, Capital Adequacy Purposes, Amount	$ 3,232	$ 3,276
Leverage, Capital Adequacy Purposes, Ratio	0.0400	0.0400
Total Capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 7,042	$ 7,064
Total Capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.1000	0.1000
Tier 1 Capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 5,633	$ 5,651
Tier 1 Capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.0800	0.0800
Common Equity Tier 1 Capital. To Be Well Capitalized Under Prompt Corrective Action, Amount	$ 4,577	$ 4,591
Common Equity Tier 1 Capital. To Be Well Capitalized Under Prompt Corrective Action, Ratio	6.50%	6.50%
Leverage, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 4,040	$ 4,095
Leverage, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.0500	0.0500