Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Net loss	$ (4)	$ (674)	$ (1,700)	$ (1,046)
Changes in:
Unrealized net capital gains and losses	(667)	(789)	(257)	(3,527)
Unrealized foreign currency translation adjustments	(14)	(88)	64	(135)
Unamortized pension and other postretirement prior service credit	(5)	(8)	(14)	(38)
Discount rate for reserve for future policy benefits	30	52	29	232
Other comprehensive loss, after-tax	(656)	(833)	(178)	(3,468)
Comprehensive loss	(660)	(1,507)	(1,878)	(4,514)
Less: Comprehensive loss attributable to noncontrolling interest	(1)	(21)	(21)	(60)
Comprehensive loss attributable to Allstate	$ (659)	$ (1,486)	$ (1,857)	$ (4,454)