Acquisitions and Dispositions (Acquired Finite-Lived Intangible Assets) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 188
Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 169
Finite-lived intangible assets, remaining amortization period	14 years
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 19
Finite-lived intangible assets, remaining amortization period	3 years 10 months 24 days