Goodwill and Long-Lived Assets - Purchased Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,333	$ 1,333
Accumulated Amortization	(780)	(738)
Reseller & customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	726	726
Accumulated Amortization	(244)	(218)
Intellectual property
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	443	443
Accumulated Amortization	$ (384)	(373)
Customer contracts
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization Period (in Years)	8 years
Gross Carrying Amount	$ 89	89
Accumulated Amortization	(88)	(87)
Tradenames
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	75	75
Accumulated Amortization	$ (64)	$ (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