Reportable Segments - Schedule of Additional Significant Financial Performance Data (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information
Amortization of DAC	$ 7,278	$ 6,634	$ 6,236
Income tax expense (benefit)	(135)	(488)	1,292
Property-Liability
Segment Reporting Information
Amortization of DAC	6,070	5,570	5,313
Income tax expense (benefit)	(136)	(427)	1,151
Protection Services
Segment Reporting Information
Amortization of DAC	1,058	928	795
Income tax expense (benefit)	66	5	39
Allstate Health and Benefits
Segment Reporting Information
Amortization of DAC	150	136	128
Income tax expense (benefit)	57	45	53
Corporate and Other
Segment Reporting Information
Income tax expense (benefit)	$ (122)	$ (111)	$ 49