Goodwill and Other Intangible Assets - Identifiable Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,776	$ 1,816
Accumulated Amortization	(1,097)	(1,105)
Net Carrying Amount	679	711
CDI
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	605	605
Accumulated Amortization	(423)	(409)
Net Carrying Amount	182	196
Other, primarily customer relationship intangibles
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,171	1,211
Accumulated Amortization	(674)	(696)
Net Carrying Amount	$ 497	$ 515