Goodwill and Purchased Intangible Assets - Schedule of Acquired Intangibles (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,218	$ 1,231
Accumulated Amortization	(717)	(653)
Reseller & customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	659	659
Accumulated Amortization	(205)	(170)
Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	397	410
Accumulated Amortization	$ (369)	(351)
Customer Contracts
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	8 years
Gross Carrying Amount	$ 89	89
Accumulated Amortization	(85)	(81)
Tradenames
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	73	73
Accumulated Amortization	$ (58)	$ (51)
Minimum [Member] | Reseller & customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	1 year
Minimum [Member] | Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	2 years
Minimum [Member] | Tradenames
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	2 years
Maximum [Member] | Reseller & customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	20 years
Maximum [Member] | Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	8 years
Maximum [Member] | Tradenames
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	10 years