Revenue from Contracts with Customers - Schedule of 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]
Total revenue	$ 3,721	$ 2,953	$ 11,551	$ 10,001
United States
Disaggregation of Revenue [Line Items]
Total revenue	2,083	1,400	5,432	4,322
Americas other than United States
Disaggregation of Revenue [Line Items]
Total revenue	263	281	948	890
United Kingdom
Disaggregation of Revenue [Line Items]
Total revenue	437	396	1,568	1,456
Ireland
Disaggregation of Revenue [Line Items]
Total revenue	38	24	106	82
Europe, Middle East, & Africa other than United Kingdom and Ireland
Disaggregation of Revenue [Line Items]
Total revenue	492	479	2,267	2,093
Asia Pacific
Disaggregation of Revenue [Line Items]
Total revenue	408	373	1,230	1,158
Eliminations
Disaggregation of Revenue [Line Items]
Total revenue	(3)	(1)	(26)	(9)
Commercial Risk Solutions | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	1,852	1,585	5,675	5,137
Reinsurance Solutions | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	503	465	2,305	2,149
Health Solutions | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	870	552	2,265	1,670
Wealth Solutions | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue	$ 499	$ 352	$ 1,332	$ 1,054