Business Segments - Segment Revenues (Detail) $ in Millions	3 Months Ended
Mar. 31, 2021 USD ($) segment	Mar. 31, 2020 USD ($)
Segment Reporting [Abstract]
Number of operating segments \| segment	2
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 2,316	$ 4,681
Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2,112	4,452
Unallocated corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	204	229
U.S. & Canada \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,721	3,820
International \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	391	632
Fee revenues
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	445	629
Contract investment amortization	(17)	(25)
Revenues	428	604
Fee revenues \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	337	508
Contract investment amortization	(17)	(25)
Revenues	320	483
Fee revenues \| U.S. & Canada \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	250	406
Contract investment amortization	(13)	(19)
Revenues	237	387
Fee revenues \| International \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	87	102
Contract investment amortization	(4)	(6)
Revenues	83	96
Owned, leased, and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	108	280
Owned, leased, and other \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	101	270
Owned, leased, and other \| U.S. & Canada \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	35	102
Owned, leased, and other \| International \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	66	168
Reimbursements
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,780	3,797
Reimbursements \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,691	3,699
Reimbursements \| U.S. & Canada \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	1,449	3,331
Reimbursements \| International \| Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 242	$ 368

Revenues, Gross of Capitalized Contract Cost, Amortization

No definition available.

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- Definition

Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
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- Definition

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).

+ References

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- References

No definition available.

+ Details

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- Definition

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.

+ References

No definition available.

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