Reportable Segments - Schedule of Additional Significant Financial Performance Data (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Segment Reporting
Amortization of DAC	$ 2,220	$ 2,101	$ 6,600	$ 6,264
Amortization of purchased intangibles	46	59	139	175
Income tax expense	537	1,075	2,058	1,802
Operating segments
Segment Reporting
Amortization of DAC	2,220	2,101	6,600	6,264
Amortization of purchased intangibles	46	59	139	175
Income tax expense	537	1,075	2,058	1,802
Operating segments \| Allstate Protection and Run-off Property-Liability
Segment Reporting
Income tax expense	535	817	2,015	1,315
Operating segments \| Allstate Protection and Run-off Property-Liability \| Allstate Protection
Segment Reporting
Amortization of DAC	1,854	1,757	5,515	5,231
Amortization of purchased intangibles	38	46	115	138
Operating segments \| Protection Services
Segment Reporting
Amortization of DAC	358	337	1,062	983
Amortization of purchased intangibles	6	10	18	28
Income tax expense	12	15	47	44
Operating segments \| Allstate Health and Benefits
Segment Reporting
Amortization of DAC	0	0	0	30
Amortization of purchased intangibles	0	0	0	1
Income tax expense	0	216	0	474
Operating segments \| Corporate
Segment Reporting
Income tax expense	(10)	29	(8)	(26)
All other
Segment Reporting
Amortization of DAC	8	7	23	20
Amortization of purchased intangibles	2	3	6	8
Income tax expense	$ 0	$ (2)	$ 4	$ (5)