Segment Information - Summarized Financial Information Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Total revenues	$ 1,258	$ 1,116
Investment income	18	7
Amortization	43	41
Depreciation	11	10
Interest expense	48	47
Income before income taxes	364	294
Total assets	14,806	13,400	$ 14,883
Capital expenditures	13	12
Operating Segments | Retail
Segment Reporting Information [Line Items]
Total revenues	806	733
Investment income	1	0
Amortization	29	28
Depreciation	5	5
Interest expense	19	22
Income before income taxes	238	214
Total assets	8,557	7,913
Capital expenditures	7	5
Operating Segments | Programs
Segment Reporting Information [Line Items]
Total revenues	298	255
Investment income	5	1
Amortization	11	11
Depreciation	4	3
Interest expense	8	10
Income before income taxes	101	75
Total assets	4,221	3,652
Capital expenditures	5	5
Operating Segments | Wholesale Brokerage
Segment Reporting Information [Line Items]
Total revenues	142	123
Investment income	1	0
Amortization	3	3
Depreciation	1	1
Interest expense	3	3
Income before income taxes	41	31
Total assets	1,617	1,441
Capital expenditures	1	0
Segment Reconciling Items
Segment Reporting Information [Line Items]
Total revenues	12	5
Investment income	11	6
Amortization	0	(1)
Depreciation	1	1
Interest expense	18	12
Income before income taxes	(16)	(26)
Total assets	411	394
Capital expenditures	$ 0	$ 2