Goodwill and Acquired Intangible Assets (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill expected to be deductible in future periods	$ 858,000,000
Goodwill, impairment loss	0	$ 0
Amortization expense for purchased finite-lived intangible assets	23,000,000	$ 17,000,000
Future amortization expense, impact of foreign currency translation adjustments	$ 97,000,000