Segment Information - Revenue from External Customers by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue from External Customer [Line Items]
Product revenue									$ 2,711	$ 2,892	$ 2,912
Professional and installation services revenue									944	971	907
Recurring revenue, including maintenance and cloud revenue									2,718	2,728	2,304
Total revenue	$ 1,680	$ 1,613	$ 1,604	$ 1,476	$ 1,768	$ 1,647	$ 1,658	$ 1,518	$ 6,373	$ 6,591	$ 6,123