Reportable Segments - Schedule of Reportable Segments Revenue Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information
Net investment income	$ 689	$ 690	$ 1,874	$ 1,846
Net gains (losses) on investments and derivatives	(86)	(167)	(223)	(1,167)
Consolidated revenues	14,497	13,208	42,262	37,763
Intersegment Eliminations
Segment Reporting Information
Consolidated revenues	(34)	(39)	(102)	(118)
Property-Liability | Operating Segments
Segment Reporting Information
Insurance premiums	12,270	11,157	35,826	32,529
Other revenue	393	364	1,135	1,066
Net investment income	627	632	1,680	1,696
Net gains (losses) on investments and derivatives	(62)	(123)	(185)	(988)
Consolidated revenues	13,228	12,030	38,456	34,303
Property-Liability | Operating Segments | Auto
Segment Reporting Information
Insurance premiums	8,345	7,545	24,374	21,974
Property-Liability | Operating Segments | Homeowners
Segment Reporting Information
Insurance premiums	2,969	2,642	8,662	7,698
Property-Liability | Operating Segments | Other personal lines
Segment Reporting Information
Insurance premiums	608	540	1,757	1,616
Property-Liability | Operating Segments | Commercial lines
Segment Reporting Information
Insurance premiums	194	296	628	874
Property-Liability | Operating Segments | Other business lines
Segment Reporting Information
Insurance premiums	154	134	405	367
Allstate Protection | Operating Segments
Segment Reporting Information
Insurance premiums	12,270	11,157	35,826	32,529
Run-off Property-Liability | Operating Segments
Segment Reporting Information
Insurance premiums	0	0	0	0
Protection Services | Operating Segments
Segment Reporting Information
Other revenue	75	84	243	269
Net investment income	19	13	53	34
Net gains (losses) on investments and derivatives	(8)	(13)	(13)	(56)
Intersegment premiums and service fees	34	39	102	118
Consolidated revenues	689	627	2,041	1,840
Protection Services | Operating Segments | Protection plans
Segment Reporting Information
Other revenue	392	330	1,126	961
Protection Services | Operating Segments | Roadside assistance
Segment Reporting Information
Other revenue	51	50	148	152
Protection Services | Operating Segments | Finance and insurance products
Segment Reporting Information
Other revenue	126	124	382	362
Allstate Health and Benefits | Operating Segments
Segment Reporting Information
Other revenue	104	90	306	277
Net investment income	20	17	60	50
Net gains (losses) on investments and derivatives	(2)	(6)	1	(25)
Consolidated revenues	585	564	1,746	1,698
Allstate Health and Benefits | Operating Segments | Employer voluntary benefits
Segment Reporting Information
Other revenue	253	257	753	777
Allstate Health and Benefits | Operating Segments | Group health
Segment Reporting Information
Other revenue	111	96	328	285
Allstate Health and Benefits | Operating Segments | Individual health
Segment Reporting Information
Other revenue	99	110	298	334
Corporate and Other | Operating Segments
Segment Reporting Information
Other revenue	20	23	66	72
Net investment income	23	28	81	66
Net gains (losses) on investments and derivatives	(14)	(25)	(26)	(98)
Consolidated revenues	$ 29	$ 26	$ 121	$ 40