Goodwill and Other Intangible Assets - Identifiable Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,945	$ 1,816
Accumulated Amortization	(1,156)	(1,105)
Net Carrying Amount	789	711
CDI
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	605	605
Accumulated Amortization	(448)	(409)
Net Carrying Amount	157	196
Other, primarily customer relationship intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,340	1,211
Accumulated Amortization	(708)	(696)
Net Carrying Amount	$ 632	$ 515