Reportable Segments - Schedule of Reportable Segments Financial Performance (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income	$ 712	$ 610	$ 1,476	$ 1,185
Net gains (losses) on investments and derivatives	(103)	(151)	(267)	(137)
Pension and other postretirement remeasurement gains (losses)	9	40	11	93
Amortization of purchased intangibles	(70)	(82)	(139)	(163)
Less: Net income (loss) attributable to noncontrolling interest	16	(23)	(4)	(24)
Net income (loss) applicable to common shareholders, basic	301	(1,389)	1,490	(1,735)
Net income (loss) applicable to common shareholders, diluted	301	(1,389)	1,490	(1,735)
Segment Reconciling Items
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	453	695	720	1,348
Net gains (losses) on investments and derivatives	(103)	(151)	(267)	(137)
Pension and other postretirement remeasurement gains (losses)	9	40	11	93
Amortization of purchased intangibles	(19)	(24)	(37)	(48)
Gain (loss) on disposition	1	(8)	5	1
Non-recurring costs	0	(90)	0	(90)
Income tax (expense) benefit on Property-Liability and reconciling	(78)	384	(337)	476
Property-Liability
Segment Reporting Information
Less: Net income (loss) attributable to noncontrolling interest	16	(23)	(4)	(24)
Property-Liability | Operating Segments
Segment Reporting Information
Underwriting income (loss) by segment	(145)	(2,094)	753	(3,095)
Allstate Protection and Run-off Property-Liability net investment income	643	544	1,345	1,053
Net gains (losses) on investments and derivatives	(103)	(135)	(265)	(123)
Property-Liability | Operating Segments | Allstate Protection
Segment Reporting Information
Underwriting income (loss) by segment	(142)	(2,092)	761	(3,090)
Property-Liability | Operating Segments | Run-off Property-Liability
Segment Reporting Information
Underwriting income (loss) by segment	(3)	(2)	(8)	(5)
Property-Liability | Segment Reconciling Items
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income	643	544	1,345	1,053
Protection Services | Operating Segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	55	41	109	75
Allstate Protection and Run-off Property-Liability net investment income	23	18	44	34
Net gains (losses) on investments and derivatives	(1)	(4)	(6)	(5)
Allstate Health and Benefits | Operating Segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	58	57	114	113
Allstate Protection and Run-off Property-Liability net investment income	25	21	48	40
Net gains (losses) on investments and derivatives	0	1	2	3
Corporate and Other | Operating Segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	(104)	(111)	(210)	(200)
Allstate Protection and Run-off Property-Liability net investment income	21	27	39	58
Net gains (losses) on investments and derivatives	$ 1	$ (13)	$ 2	$ (12)