Earnings per Share - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net Income available to common stockholders for basic net income per common share	$ 272	$ 246	$ 808	$ 671
Effect of interest on assumed conversions of convertible notes, net of tax	2	2	6	5
Net Income available to common stockholders for dilutive net income per common share	$ 274	$ 248	$ 814	$ 676
Denominator:
Weighted average common shares outstanding for basic net income per common share (in shares)	4,326	4,450	4,367	4,529
Weighted average impact of assumed convertible senior notes conversion (in shares)	29	29	29	28
Weighted average impact of dilutive equity instruments (in shares)	60	85	69	84
Weighted average shares for diluted net income per common share (in shares)	4,415	4,564	4,465	4,641
Net income per common share:
Basic (USD per share)	$ 0.06	$ 0.06	$ 0.19	$ 0.15
Diluted (USD per share)	$ 0.06	$ 0.05	$ 0.18	$ 0.15