Summary of Significant Accounting Policies - Schedule of Intangible Assets by Class (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 3,967	$ 3,695
Accumulated Amortization	2,085	1,862
Net Book Value	1,882	1,833
Customer related intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,293	2,200
Accumulated Amortization	1,168	1,043
Net Book Value	1,125	1,157
Acquired software and technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	579	507
Accumulated Amortization	460	432
Net Book Value	119	75
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	117	117
Accumulated Amortization	64	57
Net Book Value	53	60
Capitalized software development costs
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	737	641
Accumulated Amortization	282	233
Net Book Value	455	408
Purchased software
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	241	230
Accumulated Amortization	111	97
Net Book Value	$ 130	$ 133