Regulatory Capital and Restrictions - Schedule of Actual Capital Amounts and Ratios (Details) $ in Millions	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
First Horizon Corporation
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital, Actual Amount	$ 7,918	$ 7,935
Total Capital, Actual Ratio	0.1234	0.1257
Tier 1 Capital, Actual Amount	$ 7,088	$ 6,782
Tier 1 Capital, Actual Ratio	0.1104	0.1074
Common Equity Tier 1 Capital, Actual Amount	$ 6,367	$ 6,110
Common Equity Tier 1 Capital, Actual Ratio	9.92%	9.68%
Leverage, Actual Amount	$ 7,088	$ 6,782
Leverage, Actual Ratio	0.0808	0.0824
Total Capital, Capital Adequacy purposes, Amount	$ 5,135	$ 5,051
Total Capital, Capital Adequacy Purposes, Ratio	0.0800	0.0800
Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 3,851	$ 3,788
Tier 1 Capital, Capital Adequacy Purposes, Ratio	0.0600	0.0600
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 2,888	$ 2,841
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Ratio	4.50%	4.50%
Leverage, Capital Adequacy Purposes, Amount	$ 3,507	$ 3,294
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	$ 7,893	$ 7,827
Total Capital, Actual Ratio	0.1241	0.1252
Tier 1 Capital, Actual Amount	$ 7,133	$ 6,832
Tier 1 Capital, Actual Ratio	0.1122	0.1093
Common Equity Tier 1 Capital, Actual Amount	$ 6,838	$ 6,537
Common Equity Tier 1 Capital, Actual Ratio	10.75%	10.46%
Leverage, Actual Amount	$ 7,133	$ 6,832
Leverage, Actual Ratio	0.0820	0.0836
Total Capital, Capital Adequacy purposes, Amount	$ 5,088	$ 5,001
Total Capital, Capital Adequacy Purposes, Ratio	0.0800	0.0800
Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 3,816	$ 3,751
Tier 1 Capital, Capital Adequacy Purposes, Ratio	0.0600	0.0600
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Amount	$ 2,862	$ 2,813
Common Equity Tier 1 Capital, Capital Adequacy Purposes, Ratio	4.50%	4.50%
Leverage, Capital Adequacy Purposes, Amount	$ 3,478	$ 3,268
Leverage, Capital Adequacy Purposes, Ratio	0.0400	0.0400
Total Capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 6,360	$ 6,251
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	$ 5,088	$ 5,001
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	$ 4,134	$ 4,063
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	$ 4,348	$ 4,085
Leverage, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.0500	0.0500