Reportable Segments - Reportable segments financial performance (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information
Net investment income									$ 2,403	$ 3,293	$ 1,590
Pension and other postretirement remeasurement gains (losses)									(116)	644	51
Income (loss) from discontinued operations									0	(3,612)	157
Income tax benefit (expense) from discontinued operations									0	19	(10)
(Loss) income from discontinued operations, net of tax	$ 0	$ 0	$ 0	$ 0	$ (321)	$ 325	$ 196	$ (3,793)	0	(3,593)	147
Less: Net loss attributable to noncontrolling interest									(53)	(33)	0
Net (loss) income applicable to common shareholders ,Basic	(310)	$ (694)	$ (1,042)	$ 630	$ 790	$ 508	$ 1,595	$ (1,408)	$ (1,416)	1,485	5,461
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, Statement of Income or Comprehensive Income [Extensible Enumeration]									Other Income
Segment Reconciling Items
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									$ 1,474	3,425	1,068
Net gains (losses) on investments and derivatives									(1,072)	1,084	1,087
Pension and other postretirement remeasurement gains (losses)									(116)	644	51
Curtailment gains (losses)									0	0	8
Business combination expenses and amortization of purchased intangibles									(113)	(157)	(106)
Business combination fair value adjustment									0	6	0
Gain (loss) on disposition									89	0	0
Income tax benefit (expense) on reconciling items and other									496	(1,270)	(1,393)
Allstate Protection | Operating segments
Segment Reporting Information
Underwriting income									(2,782)	1,785	4,569
Run-off Property-Liability | Operating segments
Segment Reporting Information
Underwriting income									(129)	(120)	(144)
Property-Liability
Segment Reporting Information
Net investment income									2,190	3,118	1,421
Net gains (losses) on investments and derivatives									(877)	1,021	990
Less: Net loss attributable to noncontrolling interest									(52)	(34)	0
Property-Liability | Operating segments
Segment Reporting Information
Underwriting income									(2,911)	1,665	4,425
Property-Liability | Segment Reconciling Items
Segment Reporting Information
Net investment income									2,190	3,118	1,421
Protection Services
Segment Reporting Information
Net investment income									48	43	44
Net gains (losses) on investments and derivatives									(52)	25	30
Protection Services | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									169	179	153
Allstate Health and Benefits
Segment Reporting Information
Net investment income									69	74	78
Net gains (losses) on investments and derivatives									(44)	7	8
Allstate Health and Benefits | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									222	208	96
Corporate and Other
Segment Reporting Information
Gain on sale of other income	$ 83
Corporate and Other | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									(422)	(433)	(428)
Net investment income									96	58	47
Net gains (losses) on investments and derivatives									$ (99)	$ 31	$ 59