Variable Interest Entities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Variable Interest Entity [Line Items]
Net gains (losses) on investments and derivatives	$ (349)	$ (164)
Interests in surplus notes (in percent)	100.00%
Skyland
Variable Interest Entity [Line Items]
Quota share (as a percent)	100.00%
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Net gains (losses) on investments and derivatives	$ (67)	(123)
Management fee	0	10
Variable Interest Entity, Primary Beneficiary | Allstate Protection
Variable Interest Entity [Line Items]
Insurance premiums and contract charges	1	61
Costs and expenses	2	87
Variable Interest Entity, Primary Beneficiary | Consolidation, Eliminations
Variable Interest Entity [Line Items]
Ceded losses incurred	$ 1	$ 12