Reportable Segments - Schedule of Reportable Segments Revenue Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information
Net investment income	$ 764	$ 575
Net gains (losses) on investments and derivatives	(164)	14
Consolidated revenues	15,259	13,786
Intersegment Eliminations
Segment Reporting Information
Consolidated revenues	(35)	(33)
Property-Liability | Operating Segments
Segment Reporting Information
Insurance premiums	12,900	11,635
Other revenue	430	353
Net investment income	702	509
Net gains (losses) on investments and derivatives	(162)	12
Consolidated revenues	13,870	12,509
Property-Liability | Operating Segments | Allstate Protection
Segment Reporting Information
Insurance premiums	12,900	11,635
Property-Liability | Operating Segments | Run-off Property-Liability
Segment Reporting Information
Insurance premiums	0	0
Property-Liability | Operating Segments | Auto | Allstate Protection
Segment Reporting Information
Insurance premiums	8,778	7,908
Property-Liability | Operating Segments | Homeowners | Allstate Protection
Segment Reporting Information
Insurance premiums	3,154	2,810
Property-Liability | Operating Segments | Other personal lines | Allstate Protection
Segment Reporting Information
Insurance premiums	659	562
Property-Liability | Operating Segments | Commercial lines | Allstate Protection
Segment Reporting Information
Insurance premiums	169	232
Property-Liability | Operating Segments | Other business lines | Allstate Protection
Segment Reporting Information
Insurance premiums	140	123
Protection Services | Operating Segments
Segment Reporting Information
Other revenue	85	84
Net investment income	21	16
Net gains (losses) on investments and derivatives	(5)	(1)
Intersegment premiums and service fees	35	33
Consolidated revenues	748	670
Protection Services | Operating Segments | Protection plans
Segment Reporting Information
Other revenue	439	361
Protection Services | Operating Segments | Roadside assistance
Segment Reporting Information
Other revenue	47	49
Protection Services | Operating Segments | Protection and insurance products
Segment Reporting Information
Other revenue	126	128
Allstate Health and Benefits | Operating Segments
Segment Reporting Information
Other revenue	134	101
Net investment income	23	19
Net gains (losses) on investments and derivatives	2	2
Consolidated revenues	637	585
Allstate Health and Benefits | Operating Segments | Employer voluntary benefits
Segment Reporting Information
Other revenue	248	255
Allstate Health and Benefits | Operating Segments | Group health
Segment Reporting Information
Other revenue	118	107
Allstate Health and Benefits | Operating Segments | Individual health
Segment Reporting Information
Other revenue	112	101
Corporate and Other | Operating Segments
Segment Reporting Information
Other revenue	20	23
Net investment income	18	31
Net gains (losses) on investments and derivatives	1	1
Consolidated revenues	$ 39	$ 55