Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 646	$ (1,387)
Changes in:
Unrealized net capital gains and losses	(1,593)	(1,500)
Unrealized foreign currency translation adjustments	0	34
Unamortized pension and other postretirement prior service credit	(15)	(15)
Other comprehensive loss, after-tax	(1,608)	(1,481)
Comprehensive loss	(962)	(2,868)
Less: Comprehensive loss attributable to noncontrolling interest	(22)	(6)
Comprehensive loss attributable to Allstate	$ (940)	$ (2,862)