Reportable Segments - Schedule of Additional Significant Financial Performance Data (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
Amortization of DAC	$ 2,101	$ 2,037	$ 6,264	$ 5,977
Amortization of purchased intangibles	59	71	175	210
Income tax expense	1,075	254	1,802	603
Operating segments
Segment Reporting Information
Amortization of DAC	2,101	2,037	6,264	5,977
Amortization of purchased intangibles	59	71	175	210
Income tax expense	1,075	254	1,802	603
All other
Segment Reporting Information
Amortization of DAC	7	7	20	21
Amortization of purchased intangibles	3	4	8	11
Income tax expense	(2)	0	(5)	2
Allstate Protection and Run-off Property-Liability | Operating segments
Segment Reporting Information
Income tax expense	817	257	1,315	599
Allstate Protection and Run-off Property-Liability | Operating segments | Allstate Protection
Segment Reporting Information
Amortization of DAC	1,757	1,696	5,231	4,977
Amortization of purchased intangibles	46	52	138	154
Protection Services | Operating segments
Segment Reporting Information
Amortization of DAC	337	304	983	889
Amortization of purchased intangibles	10	12	28	36
Income tax expense	15	14	44	43
Allstate Health and Benefits | Operating segments
Segment Reporting Information
Amortization of DAC	0	30	30	90
Amortization of purchased intangibles	0	3	1	9
Income tax expense	216	8	474	34
Corporate | Operating segments
Segment Reporting Information
Income tax expense	$ 29	$ (25)	$ (26)	$ (75)