Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Cost	$ 4,104	$ 4,099
Accumulated Amortization	1,501	1,400
Net Carrying Amount	2,603	2,699
Client Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Cost	3,717	3,713
Accumulated Amortization	1,260	1,170
Net Carrying Amount	2,457	2,543
Other
Finite-Lived Intangible Assets [Line Items]
Gross Cost	387	386
Accumulated Amortization	241	230
Net Carrying Amount	$ 146	$ 156