Mortgage Banking Activity - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Mortgage Banking [Line Items]
Net loans and leases	$ 54,701		$ 54,701		$ 57,269
Mortgage banking and title income	34	$ 66	126	$ 72
Mortgage banking and title income
Mortgage Banking [Line Items]
Mortgage banking and title income	1	$ 1	2	$ 1
First Horizon Bank
Mortgage Banking [Line Items]
Net loans and leases	$ 48		$ 48