Reportable Segments - Schedule of Additional Significant Financial Performance Data (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Segment Reporting
Amortization of DAC	$ 2,202	$ 2,076	$ 4,380	$ 4,163
Amortization of purchased intangibles	46	57	93	116
Income tax expense	871	604	1,521	727
Operating segments
Segment Reporting
Amortization of DAC	2,202	2,076	4,380	4,163
Amortization of purchased intangibles	46	57	93	116
Income tax expense	871	604	1,521	727
Operating segments \| Allstate Protection and Run-off Property-Liability
Segment Reporting
Income tax expense	812	350	1,480	498
Operating segments \| Allstate Protection and Run-off Property-Liability \| Allstate Protection
Segment Reporting
Amortization of DAC	1,840	1,742	3,661	3,474
Amortization of purchased intangibles	38	46	77	92
Operating segments \| Protection Services
Segment Reporting
Amortization of DAC	356	328	704	646
Amortization of purchased intangibles	6	9	12	18
Income tax expense	23	16	35	29
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	249	0	258
Operating segments \| Corporate
Segment Reporting
Income tax expense	35	(9)	2	(55)
All other
Segment Reporting
Amortization of DAC	6	6	15	13
Amortization of purchased intangibles	2	2	4	5
Income tax expense	$ 1	$ (2)	$ 4	$ (3)