Revenues - Disaggregation of Revenue (Details) - 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	$ 4,906	$ 4,585	$ 9,732	$ 8,986
Time-and-materials [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,341	2,290	4,640	4,523
Fixed-price [Member]
Disaggregation of Revenue [Line Items]
Revenue	2,085	1,784	4,124	3,465
Transaction or volume-based [Member]
Disaggregation of Revenue [Line Items]
Revenue	480	511	968	998
North America [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,656	3,372	7,225	6,655
United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	458	403	911	773
Europe, excluding United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	445	482	904	938
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	903	885	1,815	1,711
Rest of World [Member]
Disaggregation of Revenue [Line Items]
Revenue	347	328	692	620
Consulting And Technology Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	3,101	2,871	6,164	5,595
Outsourcing Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,805	1,714	3,568	3,391
Financial Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,542	1,502	3,070	2,960
Financial Services [Member] | Time-and-materials [Member]
Disaggregation of Revenue [Line Items]
Revenue	894	908	1,784	1,807
Financial Services [Member] | Fixed-price [Member]
Disaggregation of Revenue [Line Items]
Revenue	578	500	1,135	971
Financial Services [Member] | Transaction or volume-based [Member]
Disaggregation of Revenue [Line Items]
Revenue	70	94	151	182
Financial Services [Member] | North America [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,104	1,049	2,184	2,062
Financial Services [Member] | United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	147	130	298	255
Financial Services [Member] | Europe, excluding United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	143	186	300	378
Financial Services [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	290	316	598	633
Financial Services [Member] | Rest of World [Member]
Disaggregation of Revenue [Line Items]
Revenue	148	137	288	265
Financial Services [Member] | Consulting And Technology Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,078	1,012	2,135	1,979
Financial Services [Member] | Outsourcing Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	464	490	935	981
Products and Resources [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,140	1,055	2,270	2,053
Products and Resources [Member] | Time-and-materials [Member]
Disaggregation of Revenue [Line Items]
Revenue	471	446	938	864
Products and Resources [Member] | Fixed-price [Member]
Disaggregation of Revenue [Line Items]
Revenue	581	506	1,153	987
Products and Resources [Member] | Transaction or volume-based [Member]
Disaggregation of Revenue [Line Items]
Revenue	88	103	179	202
Products and Resources [Member] | North America [Member]
Disaggregation of Revenue [Line Items]
Revenue	770	723	1,531	1,441
Products and Resources [Member] | United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	134	116	266	222
Products and Resources [Member] | Europe, excluding United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	143	132	288	235
Products and Resources [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	277	248	554	457
Products and Resources [Member] | Rest of World [Member]
Disaggregation of Revenue [Line Items]
Revenue	93	84	185	155
Products and Resources [Member] | Consulting And Technology Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	753	668	1,507	1,284
Products and Resources [Member] | Outsourcing Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	387	387	763	769
Communication, Media and Technology [Member]
Disaggregation of Revenue [Line Items]
Revenue	816	703	1,592	1,360
Communication, Media and Technology [Member] | Time-and-materials [Member]
Disaggregation of Revenue [Line Items]
Revenue	471	422	919	819
Communication, Media and Technology [Member] | Fixed-price [Member]
Disaggregation of Revenue [Line Items]
Revenue	309	249	601	479
Communication, Media and Technology [Member] | Transaction or volume-based [Member]
Disaggregation of Revenue [Line Items]
Revenue	36	32	72	62
Communication, Media and Technology [Member] | North America [Member]
Disaggregation of Revenue [Line Items]
Revenue	572	469	1,105	920
Communication, Media and Technology [Member] | United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	133	112	259	211
Communication, Media and Technology [Member] | Europe, excluding United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	33	44	70	87
Communication, Media and Technology [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	166	156	329	298
Communication, Media and Technology [Member] | Rest of World [Member]
Disaggregation of Revenue [Line Items]
Revenue	78	78	158	142
Communication, Media and Technology [Member] | Consulting And Technology Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	465	422	913	818
Communication, Media and Technology [Member] | Outsourcing Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	351	281	679	542
Healthcare Segment [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,408	1,325	2,800	2,613
Healthcare Segment [Member] | Time-and-materials [Member]
Disaggregation of Revenue [Line Items]
Revenue	505	514	999	1,033
Healthcare Segment [Member] | Fixed-price [Member]
Disaggregation of Revenue [Line Items]
Revenue	617	529	1,235	1,028
Healthcare Segment [Member] | Transaction or volume-based [Member]
Disaggregation of Revenue [Line Items]
Revenue	286	282	566	552
Healthcare Segment [Member] | North America [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,210	1,131	2,405	2,232
Healthcare Segment [Member] | United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	44	45	88	85
Healthcare Segment [Member] | Europe, excluding United Kingdom [Member]
Disaggregation of Revenue [Line Items]
Revenue	126	120	246	238
Healthcare Segment [Member] | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	170	165	334	323
Healthcare Segment [Member] | Rest of World [Member]
Disaggregation of Revenue [Line Items]
Revenue	28	29	61	58
Healthcare Segment [Member] | Consulting And Technology Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	805	769	1,609	1,514
Healthcare Segment [Member] | Outsourcing Services [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 603	$ 556	$ 1,191	$ 1,099