Schedule III — Supplementary Insurance Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Supplementary Insurance Information
Deferred policy acquisition costs	$ 6,163	$ 5,773	$ 5,940
Reserves for claims and claims expense, contract benefits and contractholder funds	41,350	42,186	42,093
Unearned premiums	29,080	26,909	24,709
Premium revenue and contract charges	61,449	58,309	52,516
Net investment income	3,449	3,092	2,478
Claims and claims expense and accident, health and other policy benefits	38,110	40,976	42,141
Amortization of deferred policy acquisition costs	8,389	8,039	7,278
Other operating costs and expenses	9,633	9,330	8,023
Premiums written (excluding life)	63,417	60,367	54,608
Unearned premiums	29,080	26,909
All other
Supplementary Insurance Information
Deferred policy acquisition costs	86	63	43
Reserves for claims and claims expense, contract benefits and contractholder funds	271	82	73
Unearned premiums	11	14	15
Premium revenue and contract charges	456	455	405
Net investment income	9	6	4
Claims and claims expense and accident, health and other policy benefits	277	250	183
Amortization of deferred policy acquisition costs	28	27	26
Other operating costs and expenses	336	356	314
Premiums written (excluding life)	678	433	384
Unearned premiums	11	14
Intersegment Eliminations
Supplementary Insurance Information
Deferred policy acquisition costs	0	0	0
Reserves for claims and claims expense, contract benefits and contractholder funds	0	0	0
Unearned premiums	0	0	0
Premium revenue and contract charges	(137)	(180)	(138)
Net investment income	0	0	0
Claims and claims expense and accident, health and other policy benefits	(22)	(24)	(15)
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	(115)	(156)	(123)
Premiums written (excluding life)	0	0	0
Allstate Protection and Run-off Property-Liability net investment income | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs
Reserves for claims and claims expense, contract benefits and contractholder funds
Unearned premiums
Premium revenue and contract charges
Net investment income	3,157	2,810	2,218
Claims and claims expense and accident, health and other policy benefits
Amortization of deferred policy acquisition costs
Other operating costs and expenses
Premiums written (excluding life)
Allstate Protection and Run-off Property-Liability net investment income | Operating segments | Allstate Protection
Supplementary Insurance Information
Deferred policy acquisition costs	2,803	2,548	2,378
Reserves for claims and claims expense, contract benefits and contractholder funds	39,153	39,964	37,852
Unearned premiums	23,464	21,508	19,542
Premium revenue and contract charges	57,682	53,866	48,427
Claims and claims expense and accident, health and other policy benefits	36,626	39,050	40,364
Amortization of deferred policy acquisition costs	7,003	6,676	6,070
Other operating costs and expenses	7,410	6,882	5,628
Premiums written (excluding life)	59,546	55,926	50,347
Unearned premiums	23,464	21,508
Allstate Protection and Run-off Property-Liability net investment income | Operating segments | Run-off Property-Liability
Supplementary Insurance Information
Deferred policy acquisition costs	0	0	0
Reserves for claims and claims expense, contract benefits and contractholder funds	1,852	1,883	1,942
Unearned premiums	0	0	0
Premium revenue and contract charges	0	0	0
Claims and claims expense and accident, health and other policy benefits	151	68	89
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	3	5	5
Premiums written (excluding life)	0	0	0
Protection Services | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	3,274	3,161	3,022
Reserves for claims and claims expense, contract benefits and contractholder funds	74	70	64
Unearned premiums	5,605	5,385	5,150
Premium revenue and contract charges	2,958	2,702	2,381
Net investment income	99	94	73
Claims and claims expense and accident, health and other policy benefits	699	641	632
Amortization of deferred policy acquisition costs	1,328	1,217	1,058
Other operating costs and expenses	1,273	1,138	956
Premiums written (excluding life)	3,006	2,797	2,663
Unearned premiums	5,605	5,385
Allstate Health and Benefits | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	0	1	497
Reserves for claims and claims expense, contract benefits and contractholder funds	0	187	2,162
Unearned premiums	0	2	2
Premium revenue and contract charges	490	1,466	1,441
Net investment income	24	94	78
Claims and claims expense and accident, health and other policy benefits	379	991	888
Amortization of deferred policy acquisition costs	30	119	124
Other operating costs and expenses	214	590	567
Premiums written (excluding life)	187	1,211	1,214
Unearned premiums	0	2
Corporate | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	0	0	0
Reserves for claims and claims expense, contract benefits and contractholder funds	0	0	0
Unearned premiums	0	0	0
Premium revenue and contract charges	0	0	0
Net investment income	160	88	105
Claims and claims expense and accident, health and other policy benefits	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	512	515	676
Premiums written (excluding life)	$ 0	$ 0	$ 0