Business Segments - Segment Revenues (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) segment	Mar. 31, 2021 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment	2
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of operating segments | segment	2
Revenues	$ 4,199	$ 2,316
Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,946	2,112
Unallocated corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	253	204
U.S. & Canada | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,271	1,721
International | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	675	391
Fee revenues
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	815	445
Contract investment amortization	(24)	(17)
Revenues	791	428
Fee revenues | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	666	337
Contract investment amortization	(24)	(17)
Revenues	642	320
Fee revenues | U.S. & Canada | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	489	250
Contract investment amortization	(14)	(13)
Revenues	475	237
Fee revenues | International | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	177	87
Contract investment amortization	(10)	(4)
Revenues	167	83
Owned, leased, and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	262	108
Owned, leased, and other | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	245	101
Owned, leased, and other | U.S. & Canada | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	92	35
Owned, leased, and other | International | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	153	66
Reimbursements
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,146	1,780
Reimbursements | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,059	1,691
Reimbursements | U.S. & Canada | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2,704	1,449
Reimbursements | International | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 355	$ 242