Regulatory Capital and Restrictions - Schedule of Actual Capital Amounts and Ratios (Details) $ in Millions	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
First Horizon Corporation
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital, Actual Amount	$ 9,922	$ 9,222
Total Capital, Actual Ratio	0.1396	0.1333
Tier 1 Capital, Actual Amount	$ 8,825	$ 8,247
Tier 1 Capital, Actual Ratio	0.1242	0.1192
Common Equity Tier 1 Capital, Actual Amount	$ 8,104	$ 7,032
Common Equity Tier 1 Capital, Actual Ratio	11.40%	10.17%
Leverage, Actual Amount	$ 8,825	$ 8,247
Leverage, Actual Ratio	0.1069	0.1036
Total Capital, Capital Adequacy purposes, Amount	$ 5,686	$ 5,533
Total Capital, Capital Adequacy Purposes, Ratio	0.0800	0.0800
Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 4,264	$ 4,150
Tier 1 Capital, Capital Adequacy Purposes, Ratio	0.0600	0.0600
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 3,198	$ 3,112
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Ratio	4.50%	4.50%
Leverage, Capital Adequacy Purposes, Amount	$ 3,302	$ 3,183
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	$ 9,303	$ 8,532
Total Capital, Actual Ratio	0.1317	0.1241
Tier 1 Capital, Actual Amount	$ 8,350	$ 7,700
Tier 1 Capital, Actual Ratio	0.1182	0.1120
Common Equity Tier 1 Capital, Actual Amount	$ 8,055	$ 7,405
Common Equity Tier 1 Capital, Actual Ratio	11.40%	10.77%
Leverage, Actual Amount	$ 8,350	$ 7,700
Leverage, Actual Ratio	0.1020	0.0976
Total Capital, Capital Adequacy purposes, Amount	$ 5,651	$ 5,498
Total Capital, Capital Adequacy Purposes, Ratio	0.0800	0.0800
Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 4,238	$ 4,124
Tier 1 Capital, Capital Adequacy Purposes, Ratio	0.0600	0.0600
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 3,179	$ 3,093
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Ratio	4.50%	4.50%
Leverage, Capital Adequacy Purposes, Amount	$ 3,276	$ 3,157
Leverage, Capital Adequacy Purposes, Ratio	0.0400	0.0400
Total Capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 7,064	$ 6,873
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	$ 5,651	$ 5,498
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	$ 4,591	$ 4,467
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	$ 4,095	$ 3,946
Leverage, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.0500	0.0500