Schedule III — Supplementary Insurance Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Supplementary Insurance Information
Deferred policy acquisition costs	$ 5,940	$ 5,442	$ 4,738
Reserves for claims and claims expense, contract benefits and contractholder funds	42,093	39,742	35,645
Unearned premiums	24,709	22,299	19,833
Premium revenue and contract charges	52,516	47,736	44,052
Net investment income	2,478	2,403	3,293
Claims and claims expense, contract benefits and interest credited to contractholders	42,141	38,306	30,378
Amortization of deferred policy acquisition costs	7,278	6,634	6,236
Other operating costs and expenses	8,023	8,301	7,521
Premiums written (excluding life)	54,608	50,080	45,630
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	(138)	(149)	(175)
Net investment income	0	0	0
Claims and claims expense, contract benefits and interest credited to contractholders	(15)	0	(16)
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	(123)	(149)	(159)
Premiums written (excluding life)	0	0	0
Property-Liability | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	2,378	2,146	1,951
Reserves for claims and claims expense, contract benefits and contractholder funds	39,794	37,492	33,015
Unearned premiums	19,542	17,538	15,763
Premium revenue and contract charges	48,427	43,909	40,454
Net investment income	2,218	2,190	3,118
Claims and claims expense, contract benefits and interest credited to contractholders	40,453	36,732	28,876
Amortization of deferred policy acquisition costs	6,070	5,570	5,313
Other operating costs and expenses	5,633	5,934	6,037
Premiums written (excluding life)	50,347	45,787	41,358
Allstate Protection | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	2,378	2,146	1,951
Reserves for claims and claims expense, contract benefits and contractholder funds	37,852	35,537	31,099
Unearned premiums	19,542	17,538	15,763
Premium revenue and contract charges	48,427	43,909	40,454
Claims and claims expense, contract benefits and interest credited to contractholders	40,364	36,607	28,760
Amortization of deferred policy acquisition costs	6,070	5,570	5,313
Other operating costs and expenses	5,628	5,930	6,033
Premiums written (excluding life)	50,347	45,787	41,358
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	1,942	1,955	1,916
Unearned premiums	0	0	0
Premium revenue and contract charges	0	0	0
Claims and claims expense, contract benefits and interest credited to contractholders	89	125	116
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	5	4	4
Premiums written (excluding life)	0	0	0
Protection Services | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	3,022	2,768	2,294
Reserves for claims and claims expense, contract benefits and contractholder funds	64	49	45
Unearned premiums	5,150	4,745	4,054
Premium revenue and contract charges	2,381	2,144	1,939
Net investment income	73	48	43
Claims and claims expense, contract benefits and interest credited to contractholders	632	532	458
Amortization of deferred policy acquisition costs	1,058	928	795
Other operating costs and expenses	956	952	938
Premiums written (excluding life)	2,663	2,699	2,642
Allstate Health and Benefits | Operating segments
Supplementary Insurance Information
Deferred policy acquisition costs	540	528	493
Reserves for claims and claims expense, contract benefits and contractholder funds	2,235	2,201	2,585
Unearned premiums	17	16	16
Premium revenue and contract charges	1,846	1,832	1,834
Net investment income	82	69	74
Claims and claims expense, contract benefits and interest credited to contractholders	1,071	1,042	1,060
Amortization of deferred policy acquisition costs	150	136	128
Other operating costs and expenses	881	852	838
Premiums written (excluding life)	1,598	1,594	1,630
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	105	96	58
Claims and claims expense, contract benefits and interest credited to contractholders	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	676	712	(133)
Premiums written (excluding life)	$ 0	$ 0	$ 0