Premises and Equipment - Summary of Premises and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total	$ 4,232	$ 4,279
Accumulated depreciation and amortization	(2,177)	(2,172)
Net premises and equipment	2,055	2,107
Land and land improvements
Property, Plant and Equipment [Line Items]
Total	$ 583	611
Buildings and building improvements
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	40 years
Total	$ 1,660	1,628
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total	$ 1,146	1,121
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	$ 733	791
Construction in progress
Property, Plant and Equipment [Line Items]
Total	52	62
Capitalized leases on premises and equipment
Property, Plant and Equipment [Line Items]
Total	$ 58	$ 66