Reportable Segments - Schedule of Additional Significant Financial Performance Data (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information
Amortization of DAC	$ 8,039	$ 7,278	$ 6,634
Amortization of purchased intangibles	280	329	353
Income tax expense (benefit)	1,162	(135)	(488)
Operating segments
Segment Reporting Information
Amortization of DAC	8,039	7,278	6,634
Amortization of purchased intangibles	280	329	353
Income tax expense (benefit)	1,162	(135)	(488)
Property-Liability | Operating segments
Segment Reporting Information
Amortization of DAC	6,676	6,070	5,570
Amortization of purchased intangibles	206	235	240
Income tax expense (benefit)	1,144	(136)	(427)
Protection Services | Operating segments
Segment Reporting Information
Amortization of DAC	1,217	1,058	928
Amortization of purchased intangibles	47	62	77
Income tax expense (benefit)	56	66	5
Allstate Health and Benefits | Operating segments
Segment Reporting Information
Amortization of DAC	146	150	136
Amortization of purchased intangibles	27	32	36
Income tax expense (benefit)	45	57	45
Corporate and Other | Operating segments
Segment Reporting Information
Income tax expense (benefit)	$ (83)	$ (122)	$ (111)