Acquisitions and Dispositions (Acquired Finite-Lived Intangible Assets) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 280
Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 257
Finite-lived intangible assets, remaining amortization period	13 years 3 months 18 days
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 23
Finite-lived intangible assets, remaining amortization period	4 years 6 months