General - Schedule of condensed consolidated statements of comprehensive income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss	$ (1,375)	$ (1,022)	$ (1,696)	$ (372)
Changes in:
Unrealized net capital gains and losses	(272)	(1,144)	410	(2,738)
Discount rate for reserve for future policy benefits	8	85	(1)	180
Other comprehensive (loss) income, after-tax	(241)	(1,121)	478	(2,635)
Comprehensive loss	(1,616)	(2,143)	(1,218)	(3,007)
Comprehensive loss attributable to Allstate	$ (1,592)	(2,126)	$ (1,198)	(2,968)
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss		(1,024)		(378)
Changes in:
Unrealized net capital gains and losses		(1,143)		(2,736)
Discount rate for reserve for future policy benefits		0		0
Other comprehensive (loss) income, after-tax		(1,205)		(2,813)
Comprehensive loss		(2,229)		(3,191)
Comprehensive loss attributable to Allstate		(2,212)		(3,152)
Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net loss		2		6
Changes in:
Unrealized net capital gains and losses		(1)		(2)
Discount rate for reserve for future policy benefits		85		180
Other comprehensive (loss) income, after-tax		84		178
Comprehensive loss		86		184
Comprehensive loss attributable to Allstate		$ 86		$ 184