Segment Reporting - Segment Revenue and Segment Profit (Loss) (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($) primaryreportablesegment	Mar. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Revenues	$ 1,158	$ 1,420
Revenue	$ 1,158	1,420
Primary reportable segments \| primaryreportablesegment	3
Depreciation and Amortization, excluding Amortization of Acquired Intangible Assets	$ 54	56
Segment Pre-tax Income (Loss)	69	105
Segment Adjusted EBITDA	123	161
Commercial Industries
Segment Reporting Information [Line Items]
Revenues	612	654
Revenue	612	654
Depreciation and Amortization, excluding Amortization of Acquired Intangible Assets	22	28
Segment Pre-tax Income (Loss)	113	110
Segment Adjusted EBITDA	135	138
Government services
Segment Reporting Information [Line Items]
Revenues	325	335
Revenue	325	335
Depreciation and Amortization, excluding Amortization of Acquired Intangible Assets	9	7
Segment Pre-tax Income (Loss)	86	108
Segment Adjusted EBITDA	95	115
Transportation Services
Segment Reporting Information [Line Items]
Revenues	184	176
Revenue	184	176
Depreciation and Amortization, excluding Amortization of Acquired Intangible Assets	9	8
Segment Pre-tax Income (Loss)	20	27
Segment Adjusted EBITDA	29	35
Other
Segment Reporting Information [Line Items]
Revenue	37	255
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenues	0	0
Depreciation and Amortization, excluding Amortization of Acquired Intangible Assets	14	10
Segment Pre-tax Income (Loss)	(151)	(176)
Segment Adjusted EBITDA	(137)	(166)
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Other
Segment Reporting Information [Line Items]
Revenue	36	248
Depreciation and Amortization, excluding Amortization of Acquired Intangible Assets	0	2
Segment Pre-tax Income (Loss)	1	39
Segment Adjusted EBITDA	1	41
Education \| Other
Segment Reporting Information [Line Items]
Revenue	1	7
Depreciation and Amortization, excluding Amortization of Acquired Intangible Assets	0	1
Segment Pre-tax Income (Loss)	0	(3)
Segment Adjusted EBITDA	$ 0	$ (2)

Depreciation and Amortization, excluding Amortization of Acquired Intangible Assets

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- Definition

Segment Adjusted EBITDA

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Amount of profit or loss recognized by the reportable segment.

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- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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