Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Supplementary Insurance Information
Deferred policy acquisition costs	$ 4,722	$ 3,774	$ 3,600
Reserves for claims and claims expense, contract benefits and contractholder funds	35,241	29,495	29,662
Unearned premiums	19,844	15,946	15,340
Premium revenue and contract charges	44,039	38,167	37,221
Net investment income	3,293	1,590	1,728
Claims and claims expense, contract benefits and interest credited to contractholders	30,367	22,550	24,611
Amortization of deferred policy acquisition costs	6,252	5,477	5,353
Other operating costs and expenses	7,521	7,080	6,134
Premiums written (excluding life)	45,630	38,497	37,822
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	(175)	(147)	(154)
Net investment income	0	0	0
Claims and claims expense, contract benefits and interest credited to contractholders	(16)	(11)	(9)
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	(159)	(136)	(145)
Premiums written (excluding life)	0	0	0
Allstate Protection | Other revenue
Supplementary Insurance Information
Deferred policy acquisition costs	1,951	1,608	1,624
Reserves for claims and claims expense, contract benefits and contractholder funds	31,099	25,679	25,843
Unearned premiums	15,763	12,772	12,567
Premium revenue and contract charges	40,454	35,580	34,843
Claims and claims expense, contract benefits and interest credited to contractholders	28,760	21,485	23,517
Amortization of deferred policy acquisition costs	5,313	4,642	4,649
Other operating costs and expenses	6,033	5,741	4,622
Premiums written (excluding life)	41,358	35,768	35,419
Run-off Property-Liability | Other revenue
Supplementary Insurance Information
Deferred policy acquisition costs	0	0	0
Reserves for claims and claims expense, contract benefits and contractholder funds	1,916	1,888	1,818
Unearned premiums	0	0	0
Premium revenue and contract charges	0	0	0
Claims and claims expense, contract benefits and interest credited to contractholders	116	141	105
Amortization of deferred policy acquisition costs	0	0	0
Other operating costs and expenses	4	3	3
Premiums written (excluding life)	0	0	0
Property and casualty | Other revenue
Supplementary Insurance Information
Deferred policy acquisition costs	1,951	1,608	1,624
Reserves for claims and claims expense, contract benefits and contractholder funds	33,015	27,567	27,661
Unearned premiums	15,763	12,772	12,567
Premium revenue and contract charges	40,454	35,580	34,843
Net investment income	3,118	1,421	1,533
Claims and claims expense, contract benefits and interest credited to contractholders	28,876	21,626	23,622
Amortization of deferred policy acquisition costs	5,313	4,642	4,649
Other operating costs and expenses	6,037	5,744	4,625
Premiums written (excluding life)	41,358	35,768	35,419
Protection Services | Other revenue
Supplementary Insurance Information
Deferred policy acquisition costs	2,294	1,696	1,449
Reserves for claims and claims expense, contract benefits and contractholder funds	45	43	51
Unearned premiums	4,054	3,167	2,765
Premium revenue and contract charges	1,939	1,640	1,387
Net investment income	43	44	42
Claims and claims expense, contract benefits and interest credited to contractholders	458	386	363
Amortization of deferred policy acquisition costs	795	658	543
Other operating costs and expenses	938	760	838
Premiums written (excluding life)	2,642	1,890	1,535
Allstate Health and Benefits | Other revenue
Supplementary Insurance Information
Deferred policy acquisition costs	477	470	527
Reserves for claims and claims expense, contract benefits and contractholder funds	2,181	1,885	1,950
Unearned premiums	27	7	8
Premium revenue and contract charges	1,821	1,094	1,145
Net investment income	74	78	83
Claims and claims expense, contract benefits and interest credited to contractholders	1,049	549	635
Amortization of deferred policy acquisition costs	144	177	161
Other operating costs and expenses	838	323	285
Premiums written (excluding life)	1,630	839	868
Corporate and Other | Other revenue
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	58	47	70
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	(133)	389	531
Premiums written (excluding life)	$ 0	$ 0	$ 0