Reportable Segments - Schedule of Reportable Segments Financial Performance (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information
Property-Liability net investment income									$ 2,478	$ 2,403	$ 3,293
Pension and other postretirement remeasurement gains (losses)									(9)	(116)	644
Income (loss) from discontinued operations									0	0	(3,612)
Income tax benefit from discontinued operations									0	0	19
Total from discontinued operations									0	0	(3,593)
Less: Net loss attributable to noncontrolling interest									(25)	(53)	(33)
Net (loss) income applicable to common shareholders, basic	$ 1,460	$ (41)	$ (1,389)	$ (346)	$ (303)	$ (685)	$ (1,040)	$ 634	(316)	(1,394)	1,500
Net (loss) income applicable to common shareholders, diluted	$ 1,460	$ (41)	$ (1,389)	$ (346)	(303)	$ (685)	$ (1,040)	$ 634	$ (316)	(1,394)	1,500
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									$ 1,911	1,473	3,425
Net gains (losses) on investments and derivatives									(300)	(1,072)	1,084
Pension and other postretirement remeasurement gains (losses)									(9)	(116)	644
Business combination expenses and amortization of purchased intangibles									(94)	(113)	(157)
Business combination fair value adjustment									0	0	6
Gain (loss) on disposition									4	89	0
Non-recurring costs									(90)	0	0
Income tax benefit (expense) on reconciling items									182	495	(1,270)
Property-Liability
Segment Reporting Information
Less: Net loss attributable to noncontrolling interest									(24)	(52)	(34)
Property-Liability | Operating segments
Segment Reporting Information
Underwriting income (loss) by segment									(2,184)	(2,911)	1,665
Property-Liability net investment income									2,218	2,190	3,118
Net gains (losses) on investments and derivatives									(292)	(877)	1,021
Property-Liability | Operating segments | Allstate Protection
Segment Reporting Information
Underwriting income (loss) by segment									(2,090)	(2,782)	1,785
Property-Liability | Operating segments | Run-off Property-Liability
Segment Reporting Information
Underwriting income (loss) by segment									(94)	(129)	(120)
Property-Liability | Segment Reconciling Items
Segment Reporting Information
Property-Liability net investment income									2,218	2,190	3,118
Protection Services | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									106	169	179
Property-Liability net investment income									73	48	43
Net gains (losses) on investments and derivatives									0	(52)	25
Allstate Health and Benefits | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									242	245	223
Property-Liability net investment income									82	69	74
Net gains (losses) on investments and derivatives									3	(44)	7
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									(415)	(422)	(433)
Property-Liability net investment income									105	96	58
Net gains (losses) on investments and derivatives									$ (11)	$ (99)	$ 31