Reportable Segments - Schedule of Reportable Segments Financial Performance (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income									$ 3,449	$ 3,092	$ 2,478
Net gains (losses) on investments and derivatives									(168)	(225)	(300)
Pension and other postretirement remeasurement gains (losses)									35	37	(9)
Gain on disposition of operations									1,603	0	0
Less: Net loss attributable to noncontrolling interest									(16)	(68)	(25)
Net income (loss) applicable to common shareholders, basic	$ 3,803	$ 3,717	$ 2,079	$ 566	$ 1,899	$ 1,161	$ 301	$ 1,189	10,165	4,550	(316)
Net income (loss) applicable to common shareholders, diluted	$ 3,803	$ 3,717	$ 2,079	$ 566	$ 1,899	$ 1,161	$ 301	$ 1,189	10,165	4,550	(316)
All other
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									1,711	1,456	1,958
Net gains (losses) on investments and derivatives									(168)	(225)	(300)
Pension and other postretirement remeasurement gains (losses)									35	37	(9)
Amortization of purchased intangibles									(48)	(74)	(94)
Gain on disposition of operations									1,616	16	4
All other									3	30	47
Non-recurring costs									0	0	(90)
Income tax (expense) benefit on Property-Liability and reconciling items									(2,884)	(1,138)	182
Allstate Protection
Segment Reporting Information
Less: Net loss attributable to noncontrolling interest									(15)	(67)	(24)
Allstate Protection | Operating segments
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income									3,157	2,810	2,218
Net gains (losses) on investments and derivatives									(237)	(228)	(292)
Allstate Protection | Operating segments | Allstate Protection
Segment Reporting Information
Underwriting income (loss) by segment									8,694	3,153	(2,090)
Allstate Protection | Operating segments | Run-off Property-Liability
Segment Reporting Information
Underwriting income (loss) by segment									(154)	(73)	(94)
Allstate Protection | All other
Segment Reporting Information
Allstate Protection and Run-off Property-Liability net investment income									3,157	2,810	2,218
Protection Services | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									218	217	106
Allstate Protection and Run-off Property-Liability net investment income									99	94	73
Net gains (losses) on investments and derivatives									4	(14)	0
Allstate Health and Benefits | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									43	156	195
Allstate Protection and Run-off Property-Liability net investment income									24	94	78
Net gains (losses) on investments and derivatives									(1)	(4)	5
Corporate | Operating segments
Segment Reporting Information
Adjusted net income (loss) by segment, after-tax									(362)	(426)	(415)
Allstate Protection and Run-off Property-Liability net investment income									160	88	105
Net gains (losses) on investments and derivatives									$ 67	$ 22	$ (11)