Premises, Equipment & Lease Commitments Premises, Equipment & Lease Commitments - Components of Premises and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	$ 8,264	$ 7,487
Less: Accumulated depreciation and amortization	(4,231)	(3,812)
Total premises and equipment, net	4,033	3,675
Land
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	406	423
Buildings and improvements
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	3,302	2,958
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	1,901	1,834
Computer software
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	1,753	1,681
In progress
Property, Plant and Equipment [Line Items]
Total premises and equipment, gross	$ 902	$ 591