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Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Revenue recognized that was included in contract liabilities	$ 191
Remaining performance obligations	3,600
Operating lease assets	433			$ 0
Present value of lease liabilities	508
ASU 2016-02
Related Party Transaction [Line Items]
Operating lease assets			$ 448
Present value of lease liabilities			521
Deferred rent liabilities			$ 73
Banco Bradesco SA
Related Party Transaction [Line Items]
Revenue from related party	19	$ 4
Banco Bradesco SA
Related Party Transaction [Line Items]
Receivables outstanding from related party	$ 7			$ 15
NCR Manaus
Related Party Transaction [Line Items]
Percentage of voting equity interest sold	49.00%