Goodwill and Other Intangible Assets - Identifiable Intangible Assets Subject to Amortization (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,816	$ 2,074
Accumulated Amortization	(1,105)	(1,220)
Net Carrying Amount	$ 711	854
CDI
Acquired Finite-Lived Intangible Assets [Line Items]
Wtd. Avg. Remaining Life	7 years
Gross Carrying Amount	$ 605	825
Accumulated Amortization	(409)	(565)
Net Carrying Amount	$ 196	260
Other, primarily customer relationship intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Wtd. Avg. Remaining Life	12 years
Gross Carrying Amount	$ 1,211	1,249
Accumulated Amortization	(696)	(655)
Net Carrying Amount	$ 515	$ 594