Reportable Segments - Schedule of Reportable Segments Financial Performance (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income										$ 3,092	$ 2,478	$ 2,403
Net gains (losses) on investments and derivatives										(225)	(300)	(1,072)
Pension and other postretirement remeasurement gains (losses)										37	(9)	(116)
Amortization of purchased intangibles										(280)	(329)	(353)
Less: Net loss attributable to noncontrolling interest										(68)	(25)	(53)
Net income (loss) applicable to common shareholders, basic	$ 1,899	$ 1,161	$ 301	$ 1,189	$ 1,460	$ (41)	$ (1,389)	$ (346)		4,550	(316)	(1,394)
Net income (loss) applicable to common shareholders, diluted	$ 1,899	$ 1,161	$ 301	$ 1,189	$ 1,460	$ (41)	$ (1,389)	$ (346)		4,550	(316)	(1,394)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal, Statement of Income or Comprehensive Income [Extensible Enumeration]									Other Income
Operating segments
Segment Reporting Information
Amortization of purchased intangibles										(280)	(329)	(353)
Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax										1,426	1,911	1,473
Net gains (losses) on investments and derivatives										(225)	(300)	(1,072)
Pension and other postretirement remeasurement gains (losses)										37	(9)	(116)
Amortization of purchased intangibles										(74)	(94)	(113)
Gain (loss) on disposition										16	4	89
Non-recurring costs										0	(90)	0
Income tax (expense) benefit on Property-Liability and reconciling items										(1,138)	182	495
Property-Liability
Segment Reporting Information
Less: Net loss attributable to noncontrolling interest										(67)	(24)	(52)
Property-Liability | Operating segments
Segment Reporting Information
Underwriting income (loss) by segment										3,080	(2,184)	(2,911)
Allstate Protection and Run-off Property-Liability net investment income										2,810	2,218	2,190
Net gains (losses) on investments and derivatives										(228)	(292)	(877)
Amortization of purchased intangibles										(206)	(235)	(240)
Property-Liability | Operating segments | Allstate Protection
Segment Reporting Information
Underwriting income (loss) by segment										3,153	(2,090)	(2,782)
Property-Liability | Operating segments | Run-off Property-Liability
Segment Reporting Information
Underwriting income (loss) by segment										(73)	(94)	(129)
Property-Liability | Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income										2,810	2,218	2,190
Protection Services | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax										217	106	169
Allstate Protection and Run-off Property-Liability net investment income										94	73	48
Net gains (losses) on investments and derivatives										(14)	0	(52)
Amortization of purchased intangibles										(47)	(62)	(77)
Allstate Health and Benefits | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax										186	242	245
Allstate Protection and Run-off Property-Liability net investment income										100	82	69
Net gains (losses) on investments and derivatives										(5)	3	(44)
Amortization of purchased intangibles										(27)	(32)	(36)
Corporate and Other | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax										(426)	(415)	(422)
Allstate Protection and Run-off Property-Liability net investment income										88	105	96
Net gains (losses) on investments and derivatives										$ 22	$ (11)	$ (99)
Gain on sale of other income									$ 83