Regulatory Capital and Restrictions - Narrative (Details)	12 Months Ended
	Dec. 31, 2024 USD ($) financialSubsidiary	Dec. 31, 2023 USD ($)	Jan. 01, 2025 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 4,382,000,000	$ 3,964,000,000
Dividend paid to parent company	$ 1,100,000,000	$ 220,000,000
Number of financial subsidiaries with covered transactions | financialSubsidiary	2
First Horizon Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 3,100,000,000
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	$ 937,000,000
Percent of capital stock and surplus threshold for credit extension to affiliates	20.00%
Maximum amount of credit bank may extend to all affiliates	$ 1,900,000,000
First Horizon Bank | Subsequent Event
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Amount available for dividend payments			$ 374,000,000
First Horizon Parent Company
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	0
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	387,000,000
First Horizon Advisors, Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	54,000,000
All Affiliates
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Covered transactions	$ 443,000,000