Variable Interest Entities - Summary Of VIE Consolidated By FHN (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets
Other assets	$ 4,135,056	$ 2,297,405
Total assets	83,029,579	43,310,900
Liabilities:
Other liabilities	1,695,868	990,094
Total liabilities	74,885,437	38,234,892
Rabbi Trusts Used for Deferred Compensation Plans
Assets
Other assets	154,783	91,873
Total assets	154,783	91,873
Liabilities:
Other liabilities	131,782	70,830
Total liabilities	$ 131,782	$ 70,830