Reportable Segments - Reportable segments revenue information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information
Insurance premiums									$ 47,737	$ 44,039	$ 38,167
Net investment income									2,403	3,293	1,590
Total revenues	$ 13,647	$ 13,208	$ 12,220	$ 12,337	$ 13,011	$ 12,480	$ 12,646	$ 12,451	51,412	50,588	41,909
Property-Liability
Segment Reporting Information
Insurance premiums									43,909	40,454	35,580
Net investment income									2,190	3,118	1,421
Net gains (losses) on investments and derivatives									(877)	1,021	990
Total revenues									46,638	46,030	38,848
Property-Liability | Auto
Segment Reporting Information
Insurance premiums									29,715	27,623	24,640
Property-Liability | Homeowners
Segment Reporting Information
Insurance premiums									10,912	9,927	8,254
Property-Liability | Other personal lines
Segment Reporting Information
Insurance premiums									2,159	2,077	1,919
Property-Liability | Commercial lines
Segment Reporting Information
Insurance premiums									1,123	827	767
Allstate Protection
Segment Reporting Information
Insurance premiums									43,909	40,454	35,580
Run-off Property-Liability
Segment Reporting Information
Insurance premiums									0	0	0
Protection Services
Segment Reporting Information
Intersegment premiums and service fees									149	175	147
Net investment income									48	43	44
Net gains (losses) on investments and derivatives									(52)	25	30
Total revenues									2,487	2,361	1,922
Protection Services | Protection Plans
Segment Reporting Information
Other revenue									1,307	1,132	909
Protection Services | Roadside assistance
Segment Reporting Information
Other revenue									202	192	188
Protection Services | Finance and insurance products
Segment Reporting Information
Other revenue									486	440	396
Allstate Health and Benefits
Segment Reporting Information
Net investment income									69	74	78
Net gains (losses) on investments and derivatives									(44)	7	8
Total revenues									2,260	2,261	1,180
Allstate Health and Benefits | Employer voluntary benefits
Segment Reporting Information
Other revenue									1,036	1,031	1,094
Allstate Health and Benefits | Group health
Segment Reporting Information
Other revenue									385	350	0
Allstate Health and Benefits | Individual health
Segment Reporting Information
Other revenue									412	440	0
Operating segments | Property-Liability
Segment Reporting Information
Other revenue									1,416	1,437	857
Operating segments | Protection Services
Segment Reporting Information
Other revenue									347	354	208
Operating segments | Allstate Health and Benefits
Segment Reporting Information
Other revenue									402	359	0
Operating segments | Corporate and Other
Segment Reporting Information
Other revenue									179	22	0
Net investment income									96	58	47
Net gains (losses) on investments and derivatives									(99)	31	59
Total revenues									176	111	106
Intersegment eliminations
Segment Reporting Information
Total revenues									$ (149)	$ (175)	$ (147)