Segment Information Geographic Area (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
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 1,680	$ 1,613	$ 1,604	$ 1,476	$ 1,768	$ 1,647	$ 1,658	$ 1,518	$ 6,373	$ 6,591	$ 6,123
UNITED STATES
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 2,909	$ 2,723	$ 2,383
Percentage of Revenues by Geographic Area									46.00%	41.00%	39.00%
Americas (Excluding United States) [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 590	$ 634	$ 647
Percentage of Revenues by Geographic Area									9.00%	10.00%	11.00%
EMEA
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 1,964	$ 2,184	$ 2,060
Percentage of Revenues by Geographic Area									31.00%	33.00%	33.00%
APJ [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 910	$ 1,050	$ 1,033
Percentage of Revenues by Geographic Area									0.00%	16.00%	17.00%