Segment Information - Summarized Financial Information Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Total revenues	$ 1,186	$ 1,068	$ 3,622	$ 3,231
Investment income	31	17	71	34
Amortization	45	41	131	123
Depreciation	11	10	33	30
Interest expense	50	48	147	143
Income before income taxes	317	242	1,028	791
Total assets	17,525	13,983	17,525	13,983	$ 14,883
Capital expenditures	23	14	62	38
Operating Segments | Retail
Segment Reporting Information [Line Items]
Total revenues	641	602	2,093	1,926
Investment income	2	0	3	0
Amortization	29	28	86	84
Depreciation	6	5	15	15
Interest expense	18	22	56	66
Income before income taxes	120	112	488	432
Total assets	8,617	8,101	8,617	8,101
Capital expenditures	16	9	44	23
Operating Segments | Programs
Segment Reporting Information [Line Items]
Total revenues	353	305	1,010	870
Investment income	6	4	17	7
Amortization	13	10	36	32
Depreciation	4	3	11	9
Interest expense	7	8	23	27
Income before income taxes	154	115	439	314
Total assets	6,558	3,884	6,558	3,884
Capital expenditures	4	3	14	11
Operating Segments | Wholesale Brokerage
Segment Reporting Information [Line Items]
Total revenues	171	150	472	412
Investment income	2	1	4	1
Amortization	3	3	9	9
Depreciation	1	1	3	3
Interest expense	3	3	9	9
Income before income taxes	56	24	145	93
Total assets	1,633	1,489	1,633	1,489
Capital expenditures	1	1	2	2
Segment Reconciling Items
Segment Reporting Information [Line Items]
Total revenues	21	11	47	23
Investment income	21	12	47	26
Amortization	0	0	0	(2)
Depreciation	0	1	4	3
Interest expense	22	15	59	41
Income before income taxes	(13)	(9)	(44)	(48)
Total assets	717	509	717	509
Capital expenditures	$ 2	$ 1	$ 2	$ 2