Segment Information - Revenue from External Customers by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customer [Line Items]
Product revenue									$ 2,737	$ 2,711	$ 2,892
Professional and installation services revenue									1,011	944	971
Recurring revenue, including maintenance and cloud revenue									2,795	2,718	2,728
Total revenue	$ 1,802	$ 1,677	$ 1,620	$ 1,444	$ 1,680	$ 1,613	$ 1,604	$ 1,476	$ 6,543	$ 6,373	$ 6,591