Acquisitions and Dispositions (Acquired Finite-Lived Intangible Assets) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 71
Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 67
Finite-lived intangible assets, remaining amortization period	11 years
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 4
Finite-lived intangible assets, remaining amortization period	5 years