Reportable Segments - Total assets and investments (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information
Assets	$ 99,440	$ 125,987
Assets held for sale	0	42,131
Investments	64,701	59,540
Deferred policy acquisition costs	4,722	3,774	$ 3,600	$ 3,457
Property-Liability
Segment Reporting Information
Assets	84,846	69,171
Investments	57,258	50,134
Deferred policy acquisition costs	1,951	1,608
Protection Services
Segment Reporting Information
Assets	6,909	6,177
Investments	1,890	1,822
Deferred policy acquisition costs	2,294	1,696
Allstate Health and Benefits
Segment Reporting Information
Assets	4,015	2,905
Investments	2,191	2,012
Deferred policy acquisition costs	477	470
Corporate and Other
Segment Reporting Information
Assets	3,670	5,603
Investments	$ 3,362	$ 5,572