Reportable Segments - Schedule of Additional Significant Financial Performance Data (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Segment Reporting Information
Amortization of DAC	$ 2,087	$ 1,939
Amortization of purchased intangibles	59	69
Income tax expense	123	266
Operating segments
Segment Reporting Information
Amortization of DAC	2,087	1,939
Amortization of purchased intangibles	59	69
Income tax expense	123	266
Property-Liability | Operating segments
Segment Reporting Information
Amortization of DAC	1,732	1,608
Amortization of purchased intangibles	46	51
Income tax expense	148	263
Protection Services | Operating segments
Segment Reporting Information
Amortization of DAC	318	289
Amortization of purchased intangibles	9	11
Income tax expense	13	13
Allstate Health and Benefits | Operating segments
Segment Reporting Information
Amortization of DAC	37	42
Amortization of purchased intangibles	4	7
Income tax expense	8	14
Corporate and Other | Operating segments
Segment Reporting Information
Income tax expense	$ (46)	$ (24)