Variable Interest Entities - Summary Of VIE Consolidated By FHN (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Assets
Other assets	$ 4,096	$ 4,169
Liabilities:
Other liabilities	2,550	2,382
Rabbi Trusts used for Deferred Compensation Plans
Assets
Other assets	186	177
Liabilities:
Other liabilities	$ 160	$ 150