Goodwill and Other Intangible Assets - Identifiable Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,770	$ 1,816
Accumulated Amortization	(1,123)	(1,105)
Net Carrying Amount	647	711
CDI
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	605	605
Accumulated Amortization	(436)	(409)
Net Carrying Amount	169	196
Other, primarily customer relationship intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,165	1,211
Accumulated Amortization	(687)	(696)
Net Carrying Amount	$ 478	$ 515