Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Cost		$ 2,083	$ 1,906
Accumulated Amortization		754	632
Net Carrying Amount		1,329	1,274
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Cost		1,837	1,672
Accumulated Amortization		611	518
Net Carrying Amount		1,226	1,154
Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Cost	[1]	246	234
Accumulated Amortization	[1]	143	114
Net Carrying Amount	[1]	$ 103	$ 120

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