Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Cost		$ 1,941	$ 1,906
Accumulated Amortization		685	632
Net Carrying Amount		1,256	1,274
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Cost		1,700	1,672
Accumulated Amortization		560	518
Net Carrying Amount		1,140	1,154
Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Cost	[1]	241	234
Accumulated Amortization	[1]	125	114
Net Carrying Amount	[1]	$ 116	$ 120

[1] Primarily non-compete agreements, trade names and developed technology.