Business Segments - Segment Revenues (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 4,681	$ 5,012
Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	4,333	4,762
Unallocated corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	348	250
North American | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,820	4,074
Asia Pacific | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	169	270
EMEA | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	344	418
Fee revenues
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	629	895
Contract investment amortization	(25)	(14)
Revenues	604	881
Fee revenues | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	484	730
Contract investment amortization	(24)	(13)
Revenues	460	717
Fee revenues | North American | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	406	528
Contract investment amortization	(19)	(11)
Revenues	387	517
Fee revenues | Asia Pacific | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	32	118
Contract investment amortization	(1)	0
Revenues	31	118
Fee revenues | EMEA | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross revenues	46	84
Contract investment amortization	(4)	(2)
Revenues	42	82
Owned, leased, and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	280	375
Owned, leased, and other | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	224	341
Owned, leased, and other | North American | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	102	178
Owned, leased, and other | Asia Pacific | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	31	41
Owned, leased, and other | EMEA | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	91	122
Reimbursements
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,797	3,756
Reimbursements | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,649	3,704
Reimbursements | North American | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	3,331	3,379
Reimbursements | Asia Pacific | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	107	111
Reimbursements | EMEA | Total segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 211	$ 214