Variable Interest Entities - Schedule of VIEs Consolidated by FHN (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Assets:
Other assets	$ 3,996	$ 4,169
Liabilities:
Other liabilities	2,315	2,382
Rabbi Trusts Used For Deferred Compensation Plans
Assets:
Other assets	195	177
Liabilities:
Other liabilities	$ 165	$ 150