Premises and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Land	$ 234	$ 229
Investment Building and Building Improvements	720	683
Fixtures and Equipment, Gross	451	458
Leasehold Improvements, Gross	135	140
Capitalized Computer Software, Gross	401	355
Property, Plant and Equipment, Gross	1,941	1,865
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	847	845
Premises and equipment, net	$ 1,094	$ 1,020