Reportable Segments - Revenue information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information
Net investment income	$ 610	$ 562	$ 1,185	$ 1,156
Net gains (losses) on investments and derivatives	(151)	(733)	(137)	(1,000)
Consolidated revenues	13,979	12,219	27,765	24,555
Intersegment Eliminations
Segment Reporting Information
Consolidated revenues	(35)	(38)	(68)	(79)
Property-Liability
Segment Reporting Information
Insurance premiums	11,921	10,874	23,556	21,372
Net investment income	544	506	1,053	1,064
Net gains (losses) on investments and derivatives	(135)	(662)	(123)	(865)
Consolidated revenues	12,719	11,073	25,228	22,273
Property-Liability | Auto
Segment Reporting Information
Insurance premiums	8,121	7,348	16,029	14,429
Property-Liability | Homeowners
Segment Reporting Information
Insurance premiums	2,883	2,566	5,693	5,056
Property-Liability | Other personal lines
Segment Reporting Information
Insurance premiums	587	545	1,149	1,076
Property-Liability | Commercial lines
Segment Reporting Information
Insurance premiums	202	295	434	578
Property-Liability | Other business lines
Segment Reporting Information
Insurance premiums	128	120	251	233
Property-Liability | Operating Segments
Segment Reporting Information
Other revenue	389	355	742	702
Allstate Protection
Segment Reporting Information
Insurance premiums	11,921	10,874	23,556	21,372
Run-off Property-Liability
Segment Reporting Information
Insurance premiums	0	0	0	0
Protection Services
Segment Reporting Information
Net investment income	18	12	34	21
Net gains (losses) on investments and derivatives	(4)	(30)	(5)	(43)
Intersegment premiums and service fees	35	38	68	79
Consolidated revenues	682	599	1,352	1,213
Protection Services | Protection plans
Segment Reporting Information
Other revenue	373	318	734	631
Protection Services | Roadside assistance
Segment Reporting Information
Other revenue	48	49	97	102
Protection Services | Finance and insurance products
Segment Reporting Information
Other revenue	128	121	256	238
Protection Services | Operating Segments
Segment Reporting Information
Other revenue	84	91	168	185
Allstate Health and Benefits
Segment Reporting Information
Net investment income	21	16	40	33
Net gains (losses) on investments and derivatives	1	(12)	3	(19)
Consolidated revenues	576	561	1,161	1,134
Allstate Health and Benefits | Employer voluntary benefits
Segment Reporting Information
Other revenue	245	257	500	520
Allstate Health and Benefits | Group health
Segment Reporting Information
Other revenue	110	95	217	189
Allstate Health and Benefits | Individual health
Segment Reporting Information
Other revenue	98	113	199	224
Allstate Health and Benefits | Operating Segments
Segment Reporting Information
Other revenue	101	92	202	187
Corporate and Other | Operating Segments
Segment Reporting Information
Other revenue	23	25	46	49
Net investment income	27	28	58	38
Net gains (losses) on investments and derivatives	(13)	(29)	(12)	(73)
Consolidated revenues	$ 37	$ 24	$ 92	$ 14