Reportable Segments - Schedule of Reportable Segments Revenue Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information
Net investment income	$ 712	$ 610	$ 1,476	$ 1,185
Net gains (losses) on investments and derivatives	(103)	(151)	(267)	(137)
Consolidated revenues	15,714	13,979	30,973	27,765
Intersegment Eliminations
Segment Reporting Information
Consolidated revenues	(39)	(35)	(74)	(68)
Property-Liability | Operating Segments
Segment Reporting Information
Insurance premiums	13,339	11,921	26,239	23,556
Other revenue	441	389	871	742
Net investment income	643	544	1,345	1,053
Net gains (losses) on investments and derivatives	(103)	(135)	(265)	(123)
Consolidated revenues	14,320	12,719	28,190	25,228
Property-Liability | Operating Segments | Allstate Protection
Segment Reporting Information
Insurance premiums	13,339	11,921	26,239	23,556
Property-Liability | Operating Segments | Run-off Property-Liability
Segment Reporting Information
Insurance premiums	0	0	0	0
Property-Liability | Operating Segments | Auto | Allstate Protection
Segment Reporting Information
Insurance premiums	9,079	8,121	17,857	16,029
Property-Liability | Operating Segments | Homeowners | Allstate Protection
Segment Reporting Information
Insurance premiums	3,255	2,883	6,409	5,693
Property-Liability | Operating Segments | Other personal lines | Allstate Protection
Segment Reporting Information
Insurance premiums	701	587	1,360	1,149
Property-Liability | Operating Segments | Commercial lines | Allstate Protection
Segment Reporting Information
Insurance premiums	158	202	327	434
Property-Liability | Operating Segments | Other business lines | Allstate Protection
Segment Reporting Information
Insurance premiums	146	128	286	251
Protection Services | Operating Segments
Segment Reporting Information
Other revenue	98	84	183	168
Net investment income	23	18	44	34
Net gains (losses) on investments and derivatives	(1)	(4)	(6)	(5)
Intersegment premiums and service fees	39	35	74	68
Consolidated revenues	772	682	1,520	1,352
Protection Services | Operating Segments | Protection plans
Segment Reporting Information
Other revenue	453	373	892	734
Protection Services | Operating Segments | Roadside assistance
Segment Reporting Information
Other revenue	34	48	81	97
Protection Services | Operating Segments | Protection and insurance products
Segment Reporting Information
Other revenue	126	128	252	256
Allstate Health and Benefits | Operating Segments
Segment Reporting Information
Other revenue	121	101	255	202
Net investment income	25	21	48	40
Net gains (losses) on investments and derivatives	0	1	2	3
Consolidated revenues	620	576	1,257	1,161
Allstate Health and Benefits | Operating Segments | Employer voluntary benefits
Segment Reporting Information
Other revenue	246	245	494	500
Allstate Health and Benefits | Operating Segments | Group health
Segment Reporting Information
Other revenue	120	110	238	217
Allstate Health and Benefits | Operating Segments | Individual health
Segment Reporting Information
Other revenue	108	98	220	199
Corporate and Other | Operating Segments
Segment Reporting Information
Other revenue	19	23	39	46
Net investment income	21	27	39	58
Net gains (losses) on investments and derivatives	1	(13)	2	(12)
Consolidated revenues	$ 41	$ 37	$ 80	$ 92