Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Intangible assets:
Gross Carrying Amount	$ 1,440		$ 1,440		$ 1,419
Accumulated Amortization	(1,348)		(1,348)		(1,317)
Intangible Assets, Net	92		92		102
Amortization expense	16	$ 11	32	$ 23
Customer lists and user base
Intangible assets:
Gross Carrying Amount	442		442		434
Accumulated Amortization	(408)		(408)		(393)
Intangible Assets, Net	34		$ 34		$ 41
Weighted Average Useful Life (Years)			5 years		5 years
Marketing related
Intangible assets:
Gross Carrying Amount	580		$ 580		$ 568
Accumulated Amortization	(552)		(552)		(555)
Intangible Assets, Net	28		$ 28		$ 13
Weighted Average Useful Life (Years)			5 years		5 years
Developed technologies
Intangible assets:
Gross Carrying Amount	263		$ 263		$ 263
Accumulated Amortization	(242)		(242)		(229)
Intangible Assets, Net	21		$ 21		$ 34
Weighted Average Useful Life (Years)			3 years		3 years
All other
Intangible assets:
Gross Carrying Amount	155		$ 155		$ 154
Accumulated Amortization	(146)		(146)		(140)
Intangible Assets, Net	$ 9		$ 9		$ 14
Weighted Average Useful Life (Years)			4 years		4 years