Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Intangible assets:
Gross Carrying Amount	$ 1,085		$ 1,085		$ 1,087
Accumulated Amortization	(1,066)		(1,066)		(1,048)
Net Carrying Amount	19		19		39
Amortization expense	6	$ 8	21	$ 26
Customer lists and user base
Intangible assets:
Gross Carrying Amount	356		356		356
Accumulated Amortization	(341)		(341)		(321)
Net Carrying Amount	15		$ 15		$ 35
Weighted Average Useful Life (Years)			3 years		5 years
Marketing related
Intangible assets:
Gross Carrying Amount	355		$ 355		$ 360
Accumulated Amortization	(355)		(355)		(360)
Net Carrying Amount	0		$ 0		$ 0
Weighted Average Useful Life (Years)			0 years		5 years
Developed technologies
Intangible assets:
Gross Carrying Amount	215		$ 215		$ 216
Accumulated Amortization	(215)		(215)		(214)
Net Carrying Amount	0		$ 0		$ 2
Weighted Average Useful Life (Years)			0 years		3 years
All other
Intangible assets:
Gross Carrying Amount	159		$ 159		$ 155
Accumulated Amortization	(155)		(155)		(153)
Net Carrying Amount	$ 4		$ 4		$ 2
Weighted Average Useful Life (Years)			3 years		4 years