Segment Information - Revenue from External Customers by Products and Services (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenue from External Customer [Line Items]
Product revenue	$ 721	$ 701	$ 2,077	$ 2,111
Professional and installation services revenue	436	324	1,250	900
Total solution revenue	1,157	1,025	3,327	3,011
Support services revenue	490	483	1,496	1,442
Total revenue	$ 1,647	$ 1,508	$ 4,823	$ 4,453