Reportable Segments - Schedule of Reportable Segments Revenue Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information
Insurance premiums									$ 58,309	$ 52,516	$ 47,736
Net investment income									3,092	2,478	2,403
Net gains (losses) on investments and derivatives									(225)	(300)	(1,072)
Total revenues	$ 16,506	$ 16,627	$ 15,714	$ 15,259	$ 14,832	$ 14,497	$ 13,979	$ 13,786	64,106	57,094	51,411
Operating segments | Property-Liability
Segment Reporting Information
Insurance premiums									53,866	48,427	43,909
Other revenue									1,895	1,545	1,416
Net investment income									2,810	2,218	2,190
Net gains (losses) on investments and derivatives									(228)	(292)	(877)
Total revenues									58,343	51,898	46,638
Operating segments | Property-Liability | Allstate Protection
Segment Reporting Information
Insurance premiums									53,866	48,427	43,909
Operating segments | Property-Liability | Run-off Property-Liability
Segment Reporting Information
Insurance premiums									0	0	0
Operating segments | Property-Liability | Auto | Allstate Protection
Segment Reporting Information
Insurance premiums									36,475	32,940	29,715
Operating segments | Property-Liability | Homeowners | Allstate Protection
Segment Reporting Information
Insurance premiums									13,360	11,739	10,418
Operating segments | Property-Liability | Other personal lines | Allstate Protection
Segment Reporting Information
Insurance premiums									2,823	2,387	2,159
Operating segments | Property-Liability | Commercial lines | Allstate Protection
Segment Reporting Information
Insurance premiums									609	811	1,123
Operating segments | Property-Liability | Other business lines | Allstate Protection
Segment Reporting Information
Insurance premiums									599	550	494
Operating segments | Protection Services
Segment Reporting Information
Other revenue									441	319	347
Intersegment premiums and service fees									180	138	149
Net investment income									94	73	48
Net gains (losses) on investments and derivatives									(14)	0	(52)
Total revenues									3,223	2,773	2,487
Operating segments | Protection Services | Protection Plans
Segment Reporting Information
Other revenue									1,869	1,540	1,307
Operating segments | Protection Services | Roadside assistance
Segment Reporting Information
Other revenue									150	195	202
Operating segments | Protection Services | Protection and insurance products
Segment Reporting Information
Other revenue									503	508	486
Operating segments | Allstate Health and Benefits
Segment Reporting Information
Other revenue									522	447	402
Net investment income									100	82	69
Net gains (losses) on investments and derivatives									(5)	3	(44)
Total revenues									2,538	2,378	2,259
Operating segments | Allstate Health and Benefits | Employer voluntary benefits
Segment Reporting Information
Other revenue									985	1,001	1,033
Operating segments | Allstate Health and Benefits | Group health
Segment Reporting Information
Other revenue									481	440	385
Operating segments | Allstate Health and Benefits | Individual health
Segment Reporting Information
Other revenue									455	405	414
Operating segments | Corporate and Other
Segment Reporting Information
Other revenue									72	89	179
Net investment income									88	105	96
Net gains (losses) on investments and derivatives									22	(11)	(99)
Total revenues									182	183	176
Intersegment eliminations
Segment Reporting Information
Total revenues									$ (180)	$ (138)	$ (149)