Variable Interest Entities - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Mar. 31, 2024
Variable Interest Entity [Line Items]
Interests in surplus notes (as a percent)	100.00%
Line of credit	$ 0	$ 0
Insurance premiums and contract charges	$ 58,309,000,000	52,516,000,000	$ 47,736,000,000
Skyland
Variable Interest Entity [Line Items]
Quota share (as a percent)	100.00%
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Notes payable	$ 123,000,000	123,000,000
Loss of the surplus notes				$ 123,000,000
Management fee	24,000,000	48,000,000	46,000,000
Variable Interest Entity, Primary Beneficiary | Consolidation, Eliminations
Variable Interest Entity [Line Items]
Ceded losses incurred	40,000,000	40,000,000	6,000,000
Variable Interest Entity, Primary Beneficiary | Adirondack | National General Holdings
Variable Interest Entity [Line Items]
Line of credit, maximum borrowing capacity	15,000,000
Line of credit	0
Variable Interest Entity, Primary Beneficiary | Allstate Protection
Variable Interest Entity [Line Items]
Insurance premiums and contract charges	199,000,000	224,000,000	164,000,000
Costs and expenses	$ 280,000,000	$ 251,000,000	$ 244,000,000