Revenue, Contract Assets and Liabilities - Disaggregated Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 1,112	$ 1,387	$ 2,270	$ 2,807
Point in time
Disaggregation of Revenue [Line Items]
Revenue	34	34	73	70
Over time
Disaggregation of Revenue [Line Items]
Revenue	1,078	1,353	2,197	2,737
Commercial Industries
Disaggregation of Revenue [Line Items]
Revenue	592	626	1,204	1,280
Commercial Industries | Omni-Channel Communications
Disaggregation of Revenue [Line Items]
Revenue	192	199	403	418
Commercial Industries | Human Resource Services
Disaggregation of Revenue [Line Items]
Revenue	182	189	364	376
Commercial Industries | industry Services
Disaggregation of Revenue [Line Items]
Revenue	218	238	437	486
Government services
Disaggregation of Revenue [Line Items]
Revenue	326	341	651	676
Government services | Government Services and Health
Disaggregation of Revenue [Line Items]
Revenue	176	182	355	360
Government services | Payment Services
Disaggregation of Revenue [Line Items]
Revenue	75	83	149	165
Government services | State and Local
Disaggregation of Revenue [Line Items]
Revenue	61	62	120	124
Government services | Federal
Disaggregation of Revenue [Line Items]
Revenue	14	14	27	27
Transportation Services
Disaggregation of Revenue [Line Items]
Revenue	194	180	378	356
Transportation Services | Tolling
Disaggregation of Revenue [Line Items]
Revenue	81	71	160	143
Transportation Services | Transit
Disaggregation of Revenue [Line Items]
Revenue	62	57	116	111
Transportation Services | Photo and Parking
Disaggregation of Revenue [Line Items]
Revenue	48	48	96	94
Transportation Services | Commercial Vehicle
Disaggregation of Revenue [Line Items]
Revenue	3	4	6	8
Other
Disaggregation of Revenue [Line Items]
Revenue	0	240	37	495
Other | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disaggregation of Revenue [Line Items]
Revenue	0	238	36	486
Other | Education
Disaggregation of Revenue [Line Items]
Revenue	$ 0	$ 2	$ 1	$ 9