Reportable Segments - Schedule of Reportable Segments Expense Information Used in Measure for Segment Profit or Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information
Prior year reserve reestimates	$ (308)	$ 549	$ 1,741
Accident, health and other policy benefits	1	0	(4)
Amortization of DAC	8,039	7,278	6,634
Amortization of purchased intangibles	280	329	353
Interest expense	400	379	335
Restructuring and related charges	61	169	51
Income taxes on operations	1,162	(135)	(488)
Preferred stock dividends	117	128	105
Loss adjustment expenses, net of reinsurance	2,900	2,800	2,650
Non-catastrophe losses
Segment Reporting Information
Prior year reserve reestimates	62	573	1,723
Catastrophe losses
Segment Reporting Information
Prior year reserve reestimates	(370)	(24)	18
Loss adjustment expenses, net of reinsurance	4,960	5,640	3,110
Operating segments | Property-Liability
Segment Reporting Information
Total	52,681	52,156	48,236
Operating segments | Property-Liability | Allstate Protection
Segment Reporting Information
Claims and claims expense	34,092	34,243	31,894
Amortization of DAC	6,676	6,070	5,570
Advertising expense	1,863	638	934
Amortization of purchased intangibles	206	235	240
Restructuring and related charges	51	142	44
Other segment expenses	4,762	4,613	4,712
Total	52,608	52,062	48,107
Operating segments | Property-Liability | Allstate Protection | Non-catastrophe losses
Segment Reporting Information
Prior year reserve reestimates	(6)	485	1,601
Operating segments | Property-Liability | Allstate Protection | Catastrophe losses
Segment Reporting Information
Prior year reserve reestimates	4,964	5,636	3,112
Operating segments | Property-Liability | Run-off Property-Liability
Segment Reporting Information
Claims and claims expense	68	89	125
Other segment expenses	5	5	4
Total	73	94	129
Operating segments | Protection Services
Segment Reporting Information
Claims and claims expense	641	632	532
Amortization of DAC	1,217	1,058	928
Restructuring and related charges	2	6	2
Other segment expenses	1,090	889	874
Income taxes on operations	71	83	35
Total	3,021	2,668	2,371
Operating segments | Allstate Health and Benefits
Segment Reporting Information
Accident, health and other policy benefits	1,241	1,071	1,042
Amortization of DAC	146	150	136
Restructuring and related charges	3	7	2
Other segment expenses	915	842	814
Income taxes on operations	52	63	64
Total	2,357	2,133	2,058
Operating segments | Corporate and Other
Segment Reporting Information
Interest expense	400	379	335
Restructuring and related charges	5	13	3
Other segment expenses	163	185	262
Income taxes on operations	(99)	(99)	(92)
Preferred stock dividends	117	128	105
Total	$ 586	$ 606	$ 613