Revenues and Trade Accounts Receivable - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 5,044	$ 4,897	$ 14,654	$ 14,595
Time-and-materials
Disaggregation of Revenue [Line Items]
Revenue	2,282	2,261	6,671	6,784
Fixed-price
Disaggregation of Revenue [Line Items]
Revenue	2,300	2,189	6,669	6,442
Transaction or volume-based
Disaggregation of Revenue [Line Items]
Revenue	462	447	1,314	1,369
North America
Disaggregation of Revenue [Line Items]
Revenue	3,735	3,599	10,876	10,733
United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	482	486	1,382	1,437
Europe, excluding United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	485	484	1,438	1,439
Europe
Disaggregation of Revenue [Line Items]
Revenue	967	970	2,820	2,876
Rest of World
Disaggregation of Revenue [Line Items]
Revenue	342	328	958	986
Consulting And Technology Services
Disaggregation of Revenue [Line Items]
Revenue	3,226	3,022	9,255	9,035
Outsourcing Services
Disaggregation of Revenue [Line Items]
Revenue	1,818	1,875	5,399	5,560
Financial Services
Disaggregation of Revenue [Line Items]
Revenue	1,486	1,475	4,318	4,414
Financial Services \| Time-and-materials
Disaggregation of Revenue [Line Items]
Revenue	833	806	2,421	2,478
Financial Services \| Fixed-price
Disaggregation of Revenue [Line Items]
Revenue	608	611	1,761	1,764
Financial Services \| Transaction or volume-based
Disaggregation of Revenue [Line Items]
Revenue	45	58	136	172
Financial Services \| North America
Disaggregation of Revenue [Line Items]
Revenue	1,048	1,040	3,064	3,100
Financial Services \| United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	147	156	428	473
Financial Services \| Europe, excluding United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	156	151	457	458
Financial Services \| Europe
Disaggregation of Revenue [Line Items]
Revenue	303	307	885	931
Financial Services \| Rest of World
Disaggregation of Revenue [Line Items]
Revenue	135	128	369	383
Financial Services \| Consulting And Technology Services
Disaggregation of Revenue [Line Items]
Revenue	1,051	1,013	3,025	3,019
Financial Services \| Outsourcing Services
Disaggregation of Revenue [Line Items]
Revenue	435	462	1,293	1,395
Products and Resources
Disaggregation of Revenue [Line Items]
Revenue	1,228	1,170	3,487	3,465
Products and Resources \| Time-and-materials
Disaggregation of Revenue [Line Items]
Revenue	511	471	1,428	1,391
Products and Resources \| Fixed-price
Disaggregation of Revenue [Line Items]
Revenue	627	610	1,803	1,807
Products and Resources \| Transaction or volume-based
Disaggregation of Revenue [Line Items]
Revenue	90	89	256	267
Products and Resources \| North America
Disaggregation of Revenue [Line Items]
Revenue	828	785	2,362	2,306
Products and Resources \| United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	157	137	415	406
Products and Resources \| Europe, excluding United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	154	153	447	463
Products and Resources \| Europe
Disaggregation of Revenue [Line Items]
Revenue	311	290	862	869
Products and Resources \| Rest of World
Disaggregation of Revenue [Line Items]
Revenue	89	95	263	290
Products and Resources \| Consulting And Technology Services
Disaggregation of Revenue [Line Items]
Revenue	833	763	2,297	2,258
Products and Resources \| Outsourcing Services
Disaggregation of Revenue [Line Items]
Revenue	395	407	1,190	1,207
Communication, Media and Technology
Disaggregation of Revenue [Line Items]
Revenue	816	847	2,458	2,438
Communication, Media and Technology \| Time-and-materials
Disaggregation of Revenue [Line Items]
Revenue	439	471	1,336	1,395
Communication, Media and Technology \| Fixed-price
Disaggregation of Revenue [Line Items]
Revenue	327	328	994	926
Communication, Media and Technology \| Transaction or volume-based
Disaggregation of Revenue [Line Items]
Revenue	50	48	128	117
Communication, Media and Technology \| North America
Disaggregation of Revenue [Line Items]
Revenue	564	580	1,694	1,652
Communication, Media and Technology \| United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	131	150	401	434
Communication, Media and Technology \| Europe, excluding United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	32	41	121	120
Communication, Media and Technology \| Europe
Disaggregation of Revenue [Line Items]
Revenue	163	191	522	554
Communication, Media and Technology \| Rest of World
Disaggregation of Revenue [Line Items]
Revenue	89	76	242	232
Communication, Media and Technology \| Consulting And Technology Services
Disaggregation of Revenue [Line Items]
Revenue	447	440	1,373	1,318
Communication, Media and Technology \| Outsourcing Services
Disaggregation of Revenue [Line Items]
Revenue	369	407	1,085	1,120
Healthcare Segment
Disaggregation of Revenue [Line Items]
Revenue	1,514	1,405	4,391	4,278
Healthcare Segment \| Time-and-materials
Disaggregation of Revenue [Line Items]
Revenue	499	513	1,486	1,520
Healthcare Segment \| Fixed-price
Disaggregation of Revenue [Line Items]
Revenue	738	640	2,111	1,945
Healthcare Segment \| Transaction or volume-based
Disaggregation of Revenue [Line Items]
Revenue	277	252	794	813
Healthcare Segment \| North America
Disaggregation of Revenue [Line Items]
Revenue	1,295	1,194	3,756	3,675
Healthcare Segment \| United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	47	43	138	124
Healthcare Segment \| Europe, excluding United Kingdom
Disaggregation of Revenue [Line Items]
Revenue	143	139	413	398
Healthcare Segment \| Europe
Disaggregation of Revenue [Line Items]
Revenue	190	182	551	522
Healthcare Segment \| Rest of World
Disaggregation of Revenue [Line Items]
Revenue	29	29	84	81
Healthcare Segment \| Consulting And Technology Services
Disaggregation of Revenue [Line Items]
Revenue	895	806	2,560	2,440
Healthcare Segment \| Outsourcing Services
Disaggregation of Revenue [Line Items]
Revenue	$ 619	$ 599	$ 1,831	$ 1,838