Goodwill and Acquired Intangible Assets (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Indefinite-lived Intangible Assets [Line Items]
Goodwill, impairment loss	$ 0	$ 0
Amortization expense of acquired intangible assets	25,000,000	$ 26,000,000
Net future amortization expense	990,000,000		$ 1,017,000,000
Foreign currency translation adjustment
Indefinite-lived Intangible Assets [Line Items]
Net future amortization expense	$ (108,000,000)		$ (104,000,000)