Goodwill and Acquired Intangible Assets (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Indefinite-lived Intangible Assets [Line Items]
Goodwill, impairment loss			$ 0	$ 0
Amortization expense of acquired intangible assets	$ 26,000,000	$ 25,000,000	76,000,000	$ 76,000,000
Net future amortization expense	968,000,000		968,000,000		$ 1,017,000,000
Foreign currency translation adjustment
Indefinite-lived Intangible Assets [Line Items]
Net future amortization expense	$ (74,000,000)		$ (74,000,000)		$ (104,000,000)