Regulatory Capital and Restrictions - Narrative (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) financialSubsidiary	Dec. 31, 2021 USD ($)	Jan. 31, 2023 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 3,430,000,000	$ 2,891,000,000
Dividend paid to parent company	$ 435,000,000	$ 770,000,000
Number of financial subsidiaries with covered transactions | financialSubsidiary	2
First Horizon Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 2,700,000,000
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	$ 876,000,000
Covered transactions	$ 0
Percent of capital stock and surplus threshold for credit extension to affiliates	20.00%
Maximum amount of credit bank may extend to all affiliates	$ 1,800,000,000
840 Denning LLC
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	2,000,000
FHN Financial Securities Corp.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	402,000,000
First Horizon Advisors, Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	55,000,000
All Affiliates Member
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	$ 459,000,000
Subsequent Event | First Horizon Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount available for dividend payments			$ 893,000,000