Revenues by Geography, Concentration of Credit Risk and Remaining Performance Obligations - Summary of Revenues by Geographical Region and Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue
Total revenues	$ 3,298	$ 2,786	$ 2,521	$ 2,754	$ 2,895	$ 2,769	$ 2,740	$ 2,684	$ 11,359	$ 11,088	$ 10,412
Americas
Disaggregation of Revenue
Total revenues									5,419	5,462	4,998
Europe and Africa
Disaggregation of Revenue
Total revenues									3,695	3,477	3,448
Asia-Pacific
Disaggregation of Revenue
Total revenues									2,245	2,149	1,966
Technology & Analytics Solutions
Disaggregation of Revenue
Total revenues									4,858	4,486	4,137
Technology & Analytics Solutions | Americas
Disaggregation of Revenue
Total revenues									2,413	2,370	2,087
Technology & Analytics Solutions | Europe and Africa
Disaggregation of Revenue
Total revenues									1,844	1,543	1,520
Technology & Analytics Solutions | Asia-Pacific
Disaggregation of Revenue
Total revenues									601	573	530
Research & Development Solutions
Disaggregation of Revenue
Total revenues									5,760	5,788	5,465
Research & Development Solutions | Americas
Disaggregation of Revenue
Total revenues									2,680	2,693	2,553
Research & Development Solutions | Europe and Africa
Disaggregation of Revenue
Total revenues									1,667	1,734	1,693
Research & Development Solutions | Asia-Pacific
Disaggregation of Revenue
Total revenues									1,413	1,361	1,219
Contract Sales & Medical Solutions
Disaggregation of Revenue
Total revenues									741	814	810
Contract Sales & Medical Solutions | Americas
Disaggregation of Revenue
Total revenues									326	399	358
Contract Sales & Medical Solutions | Europe and Africa
Disaggregation of Revenue
Total revenues									184	200	235
Contract Sales & Medical Solutions | Asia-Pacific
Disaggregation of Revenue
Total revenues									$ 231	$ 215	$ 217