Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 1,198	$ (321)
Changes in:
Unrealized net capital gains and losses	(215)	682
Unrealized foreign currency translation adjustments	8	50
Unamortized pension and other postretirement prior service credit	(1)	(4)
Discount rate for reserve for future policy benefits	25	(9)
Other comprehensive (loss) income, after-tax	(183)	719
Comprehensive income	1,015	398
Less: Comprehensive (loss) income attributable to noncontrolling interest	(19)	4
Comprehensive income attributable to Allstate	$ 1,034	$ 394