Reportable Segments - Performance data and tax items (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information
Amortization of DAC	$ 6,252	$ 5,477	$ 5,353
Income tax expense (benefit)	1,289	1,373	1,116
Property-Liability
Segment Reporting Information
Amortization of DAC	5,313	4,642	4,649
Income tax expense (benefit)	1,151	1,382	1,196
Protection Services
Segment Reporting Information
Amortization of DAC	795	658	543
Income tax expense (benefit)	39	26	(18)
Allstate Health and Benefits
Segment Reporting Information
Amortization of DAC	144	177	161
Income tax expense (benefit)	50	28	35
Corporate and Other
Segment Reporting Information
Income tax expense (benefit)	$ 49	$ (63)	$ (97)