Revenue - Schedule of Components of Interest and Other Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Book-of-business settlements		$ 2	$ 2
Interest income		39	43
Other income		2	1
Total interest and other income		43	46
HWC [Member]
Disaggregation of Revenue [Line Items]
Book-of-business settlements		2	0
Interest income		7	9
Other income		0	0
Total interest and other income		9	9
R&B [Member]
Disaggregation of Revenue [Line Items]
Book-of-business settlements		0	2
Interest income		22	28
Other income		2	1
Total interest and other income		24	31
Corporate Segment [Member]
Disaggregation of Revenue [Line Items]
Book-of-business settlements		0	0
Interest income		10	6
Other income		0	0
Total interest and other income	[1]	$ 10	$ 6

[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, adjustments to reserves and impacts from hedged revenue transactions.