Variable Interest Entities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Mar. 31, 2024	Dec. 31, 2023
Variable Interest Entity [Line Items]
Interests in surplus notes (in percent)	100.00%		100.00%
Skyland
Variable Interest Entity [Line Items]
Quota share (as a percent)	100.00%		100.00%
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Management fee	$ 2	$ 14	$ 23	$ 37
Notes payable	123		123			$ 123
Loss of the surplus notes					$ 123
Variable Interest Entity, Primary Beneficiary | National General Holdings | Adirondack
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity	15		15
Line of credit	0		0
Variable Interest Entity, Primary Beneficiary | Consolidation, Eliminations
Variable Interest Entity [Line Items]
Ceded losses incurred	(6)	10	24	27
Variable Interest Entity, Primary Beneficiary | Allstate Protection
Variable Interest Entity [Line Items]
Insurance premiums and contract charges	48	59	170	173
Costs and expenses	$ 62	$ 58	$ 207	$ 202