Reportable Segments - Schedule of Reportable Segments Revenue Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information
Insurance premiums									$ 61,449	$ 58,309	$ 52,516
Net investment income									3,449	3,092	2,478
Net gains (losses) on investments and derivatives									(168)	(225)	(300)
Total revenues	$ 17,345	$ 17,255	$ 16,633	$ 16,452	$ 16,506	$ 16,627	$ 15,714	$ 15,259	67,685	64,106	57,094
Operating segments | Allstate Protection and Run-off Property-Liability net investment income
Segment Reporting Information
Other revenue									2,051	1,895	1,545
Net investment income									3,157	2,810	2,218
Net gains (losses) on investments and derivatives									(237)	(228)	(292)
Total revenues									59,733	55,761	49,972
Operating segments | Allstate Protection and Run-off Property-Liability net investment income | Run-off Property-Liability
Segment Reporting Information
Insurance premiums									0	0	0
Operating segments | Allstate Protection and Run-off Property-Liability net investment income | Total Allstate Protection insurance premiums
Segment Reporting Information
Insurance premiums									57,682	53,866	48,427
Operating segments | Allstate Protection and Run-off Property-Liability net investment income | Auto | Total Allstate Protection insurance premiums
Segment Reporting Information
Insurance premiums									38,090	36,475	32,940
Operating segments | Allstate Protection and Run-off Property-Liability net investment income | Homeowners | Total Allstate Protection insurance premiums
Segment Reporting Information
Insurance premiums									15,363	13,360	11,739
Operating segments | Allstate Protection and Run-off Property-Liability net investment income | Other personal lines | Total Allstate Protection insurance premiums
Segment Reporting Information
Insurance premiums									3,134	2,823	2,387
Operating segments | Allstate Protection and Run-off Property-Liability net investment income | Commercial lines | Total Allstate Protection insurance premiums
Segment Reporting Information
Insurance premiums									419	609	811
Operating segments | Allstate Protection and Run-off Property-Liability net investment income | Other business lines | Total Allstate Protection insurance premiums
Segment Reporting Information
Insurance premiums									676	599	550
Operating segments | Protection Services
Segment Reporting Information
Intersegment premiums and service fees									137	180	138
Other revenue									489	441	319
Net investment income									99	94	73
Net gains (losses) on investments and derivatives									4	(14)	0
Total revenues									3,550	3,223	2,773
Operating segments | Protection Services | Protection plans
Segment Reporting Information
Other revenue									2,159	1,869	1,540
Operating segments | Protection Services | Roadside assistance
Segment Reporting Information
Other revenue									160	150	195
Operating segments | Protection Services | Protection and insurance products
Segment Reporting Information
Other revenue									502	503	508
Operating segments | Allstate Health and Benefits
Segment Reporting Information
Other revenue									163	327	296
Net investment income									24	94	78
Net gains (losses) on investments and derivatives									(1)	(4)	5
Total revenues									676	1,883	1,820
Operating segments | Allstate Health and Benefits | Employer voluntary benefits
Segment Reporting Information
Other revenue									243	985	1,001
Operating segments | Allstate Health and Benefits | Group health
Segment Reporting Information
Other revenue									247	481	440
Operating segments | Corporate
Segment Reporting Information
Other revenue									81	72	89
Net investment income									160	88	105
Net gains (losses) on investments and derivatives									67	22	(11)
Total revenues									308	182	183
All other
Segment Reporting Information
Net gains (losses) on investments and derivatives									(168)	(225)	(300)
Total revenues									635	655	558
All other | Allstate Protection and Run-off Property-Liability net investment income
Segment Reporting Information
Net investment income									3,157	2,810	2,218
Intersegment eliminations
Segment Reporting Information
Total revenues									$ (137)	$ (180)	$ (138)