Segment Information and Concentrations - Revenue by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue from External Customer [Line Items]
Total revenue	$ 1,536	$ 1,517
Product revenue
Revenue from External Customer [Line Items]
Total revenue	539	526
Professional services and installation services revenue
Revenue from External Customer [Line Items]
Total revenue	238	256
Recurring revenue, including maintenance, cloud revenue and payments
Revenue from External Customer [Line Items]
Total revenue	759	735
Software
Revenue from External Customer [Line Items]
Total revenue	467	460
Services
Revenue from External Customer [Line Items]
Total revenue	585	601
Hardware
Revenue from External Customer [Line Items]
Total revenue	$ 484	$ 456