Segment Information and Concentrations - Revenue by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue from External Customer [Line Items]
Total revenue	$ 1,710	$ 1,537	$ 3,246	$ 3,054
Product revenue
Revenue from External Customer [Line Items]
Total revenue	664	525	1,203	1,051
Professional services and installation services revenue
Revenue from External Customer [Line Items]
Total revenue	270	271	508	527
Recurring revenue, including maintenance, cloud revenue and payments
Revenue from External Customer [Line Items]
Total revenue	776	741	1,535	1,476
Software
Revenue from External Customer [Line Items]
Total revenue	496	470	963	930
Services
Revenue from External Customer [Line Items]
Total revenue	622	610	1,207	1,211
Hardware
Revenue from External Customer [Line Items]
Total revenue	$ 592	$ 457	$ 1,076	$ 913