Reportable Segments - Revenue information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information
Net investment income	$ 575	$ 594
Net gains (losses) on investments and derivatives	14	(267)
Consolidated revenues	13,786	12,336
Property-Liability
Segment Reporting Information
Insurance premiums	11,635	10,498
Net investment income	509	558
Net gains (losses) on investments and derivatives	12	(203)
Consolidated revenues	12,509	11,200
Property-Liability | Auto
Segment Reporting Information
Insurance premiums	7,908	7,081
Property-Liability | Homeowners
Segment Reporting Information
Insurance premiums	2,810	2,490
Property-Liability | Other personal lines
Segment Reporting Information
Insurance premiums	562	531
Property-Liability | Commercial lines
Segment Reporting Information
Insurance premiums	232	283
Property-Liability | Other business lines
Segment Reporting Information
Insurance premiums	123	113
Allstate Protection
Segment Reporting Information
Insurance premiums	11,635	10,498
Run-off Property-Liability
Segment Reporting Information
Insurance premiums	0	0
Protection Services
Segment Reporting Information
Intersegment premiums and service fees	33	41
Net investment income	16	9
Net gains (losses) on investments and derivatives	(1)	(13)
Consolidated revenues	670	614
Protection Services | Protection plans
Segment Reporting Information
Other revenue	361	313
Protection Services | Roadside assistance
Segment Reporting Information
Other revenue	49	53
Protection Services | Finance and insurance products
Segment Reporting Information
Other revenue	128	117
Allstate Health and Benefits
Segment Reporting Information
Net investment income	19	17
Net gains (losses) on investments and derivatives	2	(7)
Consolidated revenues	585	573
Allstate Health and Benefits | Employer voluntary benefits
Segment Reporting Information
Other revenue	255	263
Allstate Health and Benefits | Group health
Segment Reporting Information
Other revenue	107	94
Allstate Health and Benefits | Individual health
Segment Reporting Information
Other revenue	101	111
Operating Segments | Property-Liability
Segment Reporting Information
Other revenue	353	347
Operating Segments | Protection Services
Segment Reporting Information
Other revenue	84	94
Operating Segments | Allstate Health and Benefits
Segment Reporting Information
Other revenue	101	95
Operating Segments | Corporate and Other
Segment Reporting Information
Other revenue	23	24
Net investment income	31	10
Net gains (losses) on investments and derivatives	1	(44)
Consolidated revenues	55	(10)
Intersegment Eliminations
Segment Reporting Information
Consolidated revenues	$ (33)	$ (41)