Goodwill and Long-Lived Assets - Purchased Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,332	$ 1,333
Accumulated Amortization	(759)	(738)
Reseller & customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	725	726
Accumulated Amortization	(231)	(218)
Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	443	443
Accumulated Amortization	$ (379)	(373)
Customer contracts
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	8 years
Gross Carrying Amount	$ 89	89
Accumulated Amortization	(87)	(87)
Tradenames
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	75	75
Accumulated Amortization	$ (62)	$ (60)
Minimum | Reseller & customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	1 year
Minimum | Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	2 years
Minimum | Tradenames
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	2 years
Maximum | Reseller & customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	20 years
Maximum | Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	8 years
Maximum | Tradenames
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	10 years