Premises and Equipment - Summary of Premises and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total	$ 4,301	$ 4,232
Accumulated depreciation and amortization	(2,183)	(2,177)
Net premises and equipment	2,118	2,055
Land and land improvements
Property, Plant and Equipment [Line Items]
Total	$ 567	583
Buildings and building improvements
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	40 years
Total	$ 1,804	1,660
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total	$ 1,136	1,146
Furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	3 years
Furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	15 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total	$ 719	733
Construction in progress
Property, Plant and Equipment [Line Items]
Total	21	52
Capitalized leases on premises and equipment
Property, Plant and Equipment [Line Items]
Total	$ 54	$ 58