Reportable Segments - Schedule of Reportable Segments Financial Performance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income	$ 783	$ 689	$ 2,259	$ 1,874
Net gains (losses) on investments and derivatives	243	(86)	(24)	(223)
Pension and other postretirement remeasurement gains (losses)	(26)	(149)	(15)	(56)
Amortization of purchased intangibles	(71)	(83)	(210)	(246)
Less: Net (loss) income attributable to noncontrolling interest	(26)	1	(30)	(23)
Net income (loss) applicable to common shareholders, basic	1,161	(41)	2,651	(1,776)
Net income (loss) applicable to common shareholders, diluted	1,161	(41)	2,651	(1,776)
Segment Reconciling Items
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	656	389	1,376	1,737
Net gains (losses) on investments and derivatives	243	(86)	(24)	(223)
Pension and other postretirement remeasurement gains (losses)	(26)	(149)	(15)	(56)
Amortization of purchased intangibles	(19)	(23)	(56)	(71)
Gain (loss) on disposition	1	(5)	6	(4)
Non-recurring costs	0	0	0	(90)
Income tax (expense) benefit on Property-Liability and reconciling items	(251)	25	(588)	501
Property-Liability
Segment Reporting Information
Less: Net (loss) income attributable to noncontrolling interest	(25)	2	(29)	(22)
Property-Liability | Operating Segments
Segment Reporting Information
Underwriting income (loss) by segment	495	(414)	1,248	(3,509)
Allstate Protection and Run-off Property-Liability net investment income	708	627	2,053	1,680
Net gains (losses) on investments and derivatives	222	(62)	(43)	(185)
Property-Liability | Operating Segments | Allstate Protection
Segment Reporting Information
Underwriting income (loss) by segment	555	(331)	1,316	(3,421)
Property-Liability | Operating Segments | Run-off Property-Liability
Segment Reporting Information
Underwriting income (loss) by segment	(60)	(83)	(68)	(88)
Property-Liability | Segment Reconciling Items
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income	708	627	2,053	1,680
Protection Services | Operating Segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	58	27	167	102
Allstate Protection and Run-off Property-Liability net investment income	24	19	68	53
Net gains (losses) on investments and derivatives	10	(8)	4	(13)
Allstate Health and Benefits | Operating Segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	37	69	151	182
Allstate Protection and Run-off Property-Liability net investment income	26	20	74	60
Net gains (losses) on investments and derivatives	(6)	(2)	(4)	1
Corporate and Other | Operating Segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	(110)	(110)	(320)	(310)
Allstate Protection and Run-off Property-Liability net investment income	25	23	64	81
Net gains (losses) on investments and derivatives	$ 17	$ (14)	$ 19	$ (26)