Regulatory Capital and Restrictions - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) financialSubsidiary	Dec. 31, 2022 USD ($)	Jan. 01, 2024 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 3,964	$ 3,430
Dividend paid to parent company	$ 220	$ 435
Number of financial subsidiaries with covered transactions | financialSubsidiary	2
First Horizon Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 3,300
Percent of capital stock and surplus threshold for credit extension to parent and certain financial subsidiaries	10.00%
Maximum amount of credit bank may extend to parent and certain financial institutions	$ 951
Percent of capital stock and surplus threshold for credit extension to affiliates	20.00%
Maximum amount of credit bank may extend to all affiliates	$ 1,900
First Horizon Bank | Subsequent Event
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount available for dividend payments			$ 1,200
First Horizon Parent Company
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	1
840 Denning LLC
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	2
FHN Financial Securities Corp.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	387
First Horizon Advisors, Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	50
All Affiliates Member
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	$ 438