General - Schedule of Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss	$ (4)	$ (674)	$ (1,700)	$ (1,046)
Changes in:
Unrealized net capital gains and losses	(667)	(789)	(257)	(3,527)
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)
Comprehensive loss attributable to Allstate	$ (659)	(1,486)	$ (1,857)	(4,454)
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss		(683)		(1,061)
Changes in:
Unrealized net capital gains and losses		(789)		(3,525)
Discount rate for reserve for future policy benefits		0		0
Other comprehensive loss, after-tax		(885)		(3,698)
Comprehensive loss		(1,568)		(4,759)
Comprehensive loss attributable to Allstate		(1,547)		(4,699)
Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss		9		15
Changes in:
Unrealized net capital gains and losses		0		(2)
Discount rate for reserve for future policy benefits		52		232
Other comprehensive loss, after-tax		52		230
Comprehensive loss		61		245
Comprehensive loss attributable to Allstate		$ 61		$ 245