Benefit Plans - Allstate 401(k) savings plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Company's contribution to the Allstate Plan	$ 110	$ 103	$ 93
ESOP benefit			(41)
Defined contribution plan expense for eligible employees of Canadian insurance subsidiaries and Sterling	$ 9	$ 13	$ 15