Reportable Segments - Schedule of Reportable Segments Financial Performance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income	$ 949	$ 783	$ 2,557	$ 2,259
Net gains (losses) on investments and derivatives	252	243	(241)	(24)
Pension and other postretirement remeasurement gains (losses)	108	(26)	30	(15)
Amortization of purchased intangibles	(59)	(71)	(175)	(210)
Gain on disposition	720	0	1,610	0
Less: Net loss attributable to noncontrolling interest	(2)	(26)	(11)	(30)
Net income applicable to common shareholders, basic	3,717	1,161	6,362	2,651
Net income applicable to common shareholders, diluted	3,717	1,161	6,362	2,651
Operating segments
Segment Reporting Information
Amortization of purchased intangibles	(59)	(71)	(175)	(210)
All other
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	863	661	1,892	1,394
Net gains (losses) on investments and derivatives	252	243	(241)	(24)
Pension and other postretirement remeasurement gains (losses)	108	(26)	30	(15)
Amortization of purchased intangibles	(13)	(19)	(37)	(56)
Gain on disposition	723	1	1,616	6
All other	(7)	5	(16)	18
Income tax (expense) benefit on Allstate Protection and Run-off Property-Liability and reconciling items	(1,073)	(251)	(1,803)	(588)
Allstate Protection
Segment Reporting Information
Less: Net loss attributable to noncontrolling interest	(1)	(25)	(10)	(29)
Allstate Protection | Operating segments
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income	873	708	2,343	2,053
Net gains (losses) on investments and derivatives	157	222	(362)	(43)
Allstate Protection | Operating segments | Allstate Protection
Segment Reporting Information
Underwriting income (loss) by segment	3,040	555	4,687	1,316
Amortization of purchased intangibles	(46)	(52)	(138)	(154)
Allstate Protection | Operating segments | Run-off Property-Liability
Segment Reporting Information
Underwriting income (loss) by segment	(146)	(60)	(153)	(68)
Allstate Protection | All other
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income	873	708	2,343	2,053
Protection Services | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	46	58	161	167
Allstate Protection and Run-off Property-Liability net investment income	25	24	74	68
Net gains (losses) on investments and derivatives	10	10	1	4
Amortization of purchased intangibles	(10)	(12)	(28)	(36)
Allstate Health and Benefits | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	0	32	43	133
Allstate Protection and Run-off Property-Liability net investment income	0	25	24	69
Net gains (losses) on investments and derivatives	0	(6)	(1)	(3)
Amortization of purchased intangibles	0	(3)	(1)	(9)
Corporate | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax	(87)	(110)	(278)	(320)
Allstate Protection and Run-off Property-Liability net investment income	49	25	108	64
Net gains (losses) on investments and derivatives	$ 85	$ 17	$ 122	$ 19