Variable Interest Entities - Summary of VIE Consolidated By FHN (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Assets:
Other assets	$ 3,542	$ 4,062
Liabilities:
Other liabilities	1,563	1,699
Rabbi Trusts Used For Deferred Compensation Plans
Assets:
Other assets	205	195
Liabilities:
Other liabilities	$ 179	$ 165