Schedule III — Supplementary Insurance Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Supplementary Insurance Information
Deferred policy acquisition costs	$ 5,773	$ 5,940	$ 5,442
Reserves for claims and claims expense, contract benefits and contractholder funds	42,186	42,093	39,742
Unearned premiums	26,909	24,709	22,299
Premium revenue and contract charges	58,309	52,516	47,736
Net investment income	3,092	2,478	2,403
Claims and claims expense and accident, health and other policy benefits	40,976	42,141	38,306
Amortization of deferred policy acquisition costs	8,039	7,278	6,634
Other operating costs and expenses	9,330	8,023	8,301
Premiums written (excluding life)	60,367	54,608	50,080
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	(180)	(138)	(149)
Net investment income	0	0	0
Claims and claims expense and accident, health and other policy benefits	(24)	(15)	0
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	(156)	(123)	(149)
Premiums written (excluding life)	0	0	0
Total Property-Liability | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	2,548	2,378	2,146
Reserves for claims and claims expense, contract benefits and contractholder funds	41,847	39,794	37,492
Unearned premiums	21,508	19,542	17,538
Premium revenue and contract charges	53,866	48,427	43,909
Net investment income	2,810	2,218	2,190
Claims and claims expense and accident, health and other policy benefits	39,118	40,453	36,732
Amortization of deferred policy acquisition costs	6,676	6,070	5,570
Other operating costs and expenses	6,887	5,633	5,934
Premiums written (excluding life)	55,926	50,347	45,787
Allstate Protection | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	2,548	2,378	2,146
Reserves for claims and claims expense, contract benefits and contractholder funds	39,964	37,852	35,537
Unearned premiums	21,508	19,542	17,538
Premium revenue and contract charges	53,866	48,427	43,909
Claims and claims expense and accident, health and other policy benefits	39,050	40,364	36,607
Amortization of deferred policy acquisition costs	6,676	6,070	5,570
Other operating costs and expenses	6,882	5,628	5,930
Premiums written (excluding life)	55,926	50,347	45,787
Run-off Property-Liability | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	0	0	0
Reserves for claims and claims expense, contract benefits and contractholder funds	1,883	1,942	1,955
Unearned premiums	0	0	0
Premium revenue and contract charges	0	0	0
Claims and claims expense and accident, health and other policy benefits	68	89	125
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	5	5	4
Premiums written (excluding life)	0	0	0
Protection Services | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	3,161	3,022	2,768
Reserves for claims and claims expense, contract benefits and contractholder funds	70	64	49
Unearned premiums	5,385	5,150	4,745
Premium revenue and contract charges	2,702	2,381	2,144
Net investment income	94	73	48
Claims and claims expense and accident, health and other policy benefits	641	632	532
Amortization of deferred policy acquisition costs	1,217	1,058	928
Other operating costs and expenses	1,138	956	952
Premiums written (excluding life)	2,797	2,663	2,699
Allstate Health and Benefits | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	64	540	528
Reserves for claims and claims expense, contract benefits and contractholder funds	269	2,235	2,201
Unearned premiums	16	17	16
Premium revenue and contract charges	1,921	1,846	1,832
Net investment income	100	82	69
Claims and claims expense and accident, health and other policy benefits	1,241	1,071	1,042
Amortization of deferred policy acquisition costs	146	150	136
Other operating costs and expenses	946	881	852
Premiums written (excluding life)	1,644	1,598	1,594
Corporate and Other | 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	88	105	96
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	515	676	712
Premiums written (excluding life)	$ 0	$ 0	$ 0