Revenue - Schedule of Revenue by Geography (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		$ 1,974	$ 2,052	$ 4,124	$ 4,253
Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,961	2,038	4,093	4,223
Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,961	2,038	4,093	4,223
Corporate, Non-Segment
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	[1]	3	1	11	6
Corporate, Non-Segment | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	[1]	6	3	12	6
HWC [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,153	1,189	2,404	2,429
HWC [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,139	1,175	2,377	2,402
HWC [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,139	1,175	2,377	2,402
R&B [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		818	853	1,709	1,758
R&B [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		816	851	1,704	1,755
R&B [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		816	851	1,704	1,755
Divested Businesses [Member]
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0	9	0	60
Divested Businesses [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0	9	0	60
Divested Businesses [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0	9	0	60
North America [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1,091	1,072	2,149	2,117
North America [Member] | Corporate, Non-Segment | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2	2	4	4
North America [Member] | HWC [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		756	738	1,535	1,510
North America [Member] | R&B [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		333	327	610	593
North America [Member] | Divested Businesses [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0	5	0	10
Europe [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		647	736	1,484	1,640
Europe [Member] | Corporate, Non-Segment | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		3	1	7	2
Europe [Member] | HWC [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		293	348	646	706
Europe [Member] | R&B [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		351	383	831	882
Europe [Member] | Divested Businesses [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		0	4	0	50
International [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		223	230	460	466
International [Member] | Corporate, Non-Segment | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		1	0	1	0
International [Member] | HWC [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		90	89	196	186
International [Member] | R&B [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		132	141	263	280
International [Member] | Divested Businesses [Member] | Operating Segments [Member] | Service
Disaggregation Of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		$ 0	$ 0	$ 0	$ 0

[1] Reimbursable expenses and other, as well as Corporate revenue, are excluded from segment revenue, but included in total revenue on the condensed consolidated statements of comprehensive income. Amounts included in Corporate revenue may include eliminations and impacts from hedged revenue transactions.