Revenue - Schedule of Components of Interest and Other Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Book-of-business settlements		$ 26	$ 71	$ 134
Interest income		145	55	12
Other income		8	14	26
Total interest and other income		179	140	172
HWC [Member]
Disaggregation of Revenue [Line Items]
Book-of-business settlements		1	19	17
Interest income		25	8	2
Other income		4	12	18
Total interest and other income		30	39	37
R&B [Member]
Disaggregation of Revenue [Line Items]
Book-of-business settlements		25	52	82
Interest income		79	25	11
Other income		3	(1)	2
Total interest and other income		107	76	95
Divested Businesses [Member]
Disaggregation of Revenue [Line Items]
Book-of-business settlements		0	0	35
Interest income		0	0	0
Other income		0	0	0
Total interest and other income		0	0	35
Corporate [Member]
Disaggregation of Revenue [Line Items]
Book-of-business settlements		0	0	0
Interest income		41	22	(1)
Other income		1	3	6
Total interest and other income	[1]	$ 42	$ 25	$ 5

[1] Reimbursable expenses and other, as well as Corporate revenue, are excluded from segment revenue, but included in total revenue on the consolidated statements of comprehensive income. Amounts included in Corporate revenue may include eliminations, adjustments to reserves and impacts from hedged revenue transactions.