Goodwill and Purchased Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Goodwill [Line Items]
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount			20.00%
Impairment of Long-Lived Assets Held-for-use	$ 21	$ 21
Impairment of Intangible Assets, Finite-lived	16	16
Goodwill [Roll Forward]
Goodwill	$ 2,758	$ 2,758	$ 2,758	$ 2,764
Accumulated Impairment Losses		(23)
Total		2,741
Additions		0
Impairment		(146)
Other		(6)
Goodwill	2,758	2,758
Accumulated Impairment Losses	(169)	(169)
Total	2,589	2,589
Software
Goodwill [Roll Forward]
Goodwill	1,938	1,938	1,938	1,944
Accumulated Impairment Losses		(7)
Total		1,937
Additions		0
Impairment		0
Other		(6)
Goodwill	1,938	1,938
Accumulated Impairment Losses	(7)	(7)
Total	1,931	1,931
Services
Goodwill [Roll Forward]
Goodwill	658	658	658	658
Accumulated Impairment Losses		0
Total		658
Additions		0
Impairment		0
Other		0
Goodwill	658	658
Accumulated Impairment Losses	0	0
Total	658	658
Hardware
Goodwill [Roll Forward]
Goodwill	162	162	$ 162	$ 162
Accumulated Impairment Losses		(16)
Total		146
Additions		0
Impairment	146	(146)
Other		0
Goodwill	162	162
Accumulated Impairment Losses	(162)	(162)
Total	$ 0	$ 0