Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Intangible assets:
Gross Carrying Amount	$ 1,493		$ 1,493		$ 1,408
Accumulated Amortization	(1,376)		(1,376)		(1,318)
Intangible Assets, Net	117		117		90
Amortization expense	15	$ 18	38	$ 50
Customer lists and user base
Intangible assets:
Gross Carrying Amount	462		462		419
Accumulated Amortization	(414)		(414)		(399)
Intangible Assets, Net	48		$ 48		$ 20
Weighted Average Useful Life (Years)			5 years		5 years
Marketing related
Intangible assets:
Gross Carrying Amount	614		$ 614		$ 594
Accumulated Amortization	(595)		(595)		(570)
Intangible Assets, Net	19		$ 19		$ 24
Weighted Average Useful Life (Years)			5 years		5 years
Developed technologies
Intangible assets:
Gross Carrying Amount	265		$ 265		$ 238
Accumulated Amortization	(230)		(230)		(215)
Intangible Assets, Net	35		$ 35		$ 23
Weighted Average Useful Life (Years)			3 years		4 years
All other
Intangible assets:
Gross Carrying Amount	152		$ 152		$ 157
Accumulated Amortization	(137)		(137)		(134)
Intangible Assets, Net	$ 15		$ 15		$ 23
Weighted Average Useful Life (Years)			4 years		4 years