Investments - Carrying Value of Equity Investments Without Readily Determinable Fair Values (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Equity Securities without Readily Determinable Fair Value [Roll Forward]
Carrying value, beginning of period	$ 136	$ 859	$ 137	$ 872
Additions	160	0	160	23
Sales	0	(718)	0	(718)
Downward adjustments for observable price changes and impairment	0	0	0	(20)
Foreign currency translation and other	(3)	(3)	(4)	(19)
Carrying value, end of period	293	$ 138	293	$ 138
Cumulative downward adjustments for price changes and impairment	$ 81		$ 81