Reportable Segments - Schedule of Additional Significant Financial Performance Data (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information
Amortization of DAC	$ 8,389	$ 8,039	$ 7,278
Amortization of purchased intangibles	231	280	329
Income tax expense (benefit)	2,890	1,162	(135)
Operating segments
Segment Reporting Information
Amortization of DAC	8,389	8,039	7,278
Amortization of purchased intangibles	231	280	329
Income tax expense (benefit)	2,890	1,162	(135)
All other
Segment Reporting Information
Amortization of DAC	28	27	26
Amortization of purchased intangibles	11	17	20
Income tax expense (benefit)	1	5	4
Allstate Protection | Operating segments
Segment Reporting Information
Income tax expense (benefit)	2,407	1,144	(136)
Allstate Protection | Operating segments | Allstate Protection
Segment Reporting Information
Amortization of DAC	7,003	6,676	6,070
Amortization of purchased intangibles	183	206	235
Protection Services | Operating segments
Segment Reporting Information
Amortization of DAC	1,328	1,217	1,058
Amortization of purchased intangibles	36	47	62
Income tax expense (benefit)	57	56	66
Allstate Health and Benefits | Operating segments
Segment Reporting Information
Amortization of DAC	30	119	124
Amortization of purchased intangibles	1	10	12
Income tax expense (benefit)	474	40	53
Corporate | Operating segments
Segment Reporting Information
Income tax expense (benefit)	$ (49)	$ (83)	$ (122)