Acquisitions and Dispositions (Acquired Finite-Lived Intangible Assets) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 190
Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 176
Finite-lived intangible assets, remaining amortization period	13 years 8 months 12 days
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 14
Finite-lived intangible assets, remaining amortization period	3 years 9 months 18 days