Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Cost	$ 4,289	$ 4,099
Accumulated Amortization	1,572	1,400
Net Carrying Amount	2,717	2,699
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Cost	3,882	3,713
Accumulated Amortization	1,320	1,170
Net Carrying Amount	2,562	2,543
Other
Finite-Lived Intangible Assets [Line Items]
Gross Cost	407	386
Accumulated Amortization	252	230
Net Carrying Amount	$ 155	$ 156