Premises, Equipment, and Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Impairment losses	$ 12	$ 27
Gain/(loss) on sale of properties, before applicable income taxes		$ 2
Direct financing and sale-type lease, interest income	$ 10
Direct financing lease, option to extend, term	12 months
Sales-type lease, option to extend, term	12 months
Minimum
Property, Plant and Equipment [Line Items]
Direct financing lease term	2 years
Sales-type lease term	2 years
Maximum
Property, Plant and Equipment [Line Items]
Direct financing lease term	23 years
Sales-type lease term	23 years