Variable Interest Entities - Summary Of VIE Consolidated By FHN (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Assets
Other assets	$ 4,582	$ 4,080
Liabilities:
Other liabilities	2,695	2,479
Rabbi Trusts used for Deferred Compensation Plans
Assets
Other assets	172	181
Liabilities:
Other liabilities	$ 144	$ 150