Variable Interest Entities - Schedule of VIE Consolidated By FHN (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets:
Other assets	$ 4,169	$ 4,080
Liabilities:
Other liabilities	2,382	2,479
Rabbi Trusts Used For Deferred Compensation Plans
Assets:
Other assets	177	181
Liabilities:
Other liabilities	$ 150	$ 150