Reportable Segments - Schedule of Reportable Segment Total Assets, Investments and Deferred Policy Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information
Assets	$ 111,617	$ 103,362
Investments	72,610	66,677
Deferred policy acquisition costs	5,773	5,940	$ 5,442	$ 4,738
Investments held for sale	824	1,055
Property-Liability
Segment Reporting Information
Assets	96,988	88,568
Investments	67,671	59,540
Deferred policy acquisition costs	2,548	2,378
Protection Services
Segment Reporting Information
Assets	7,540	7,292
Investments	2,228	2,180
Deferred policy acquisition costs	3,161	3,022
Allstate Health and Benefits
Segment Reporting Information
Assets	4,362	4,032
Investments	379	2,182
Deferred policy acquisition costs	64	540
Allstate Health and Benefits | Disposal Group, Held-for-Sale, Not Discontinued Operations
Segment Reporting Information
Investments held for sale	1,910
Deferred policy acquisition costs held for sale	521
Corporate and Other
Segment Reporting Information
Assets	2,727	3,470
Investments	$ 2,332	$ 2,775