General - Schedule of Condensed Consolidated Statements of Shareholders’ Equity (unaudited) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Increase (decrease) in equity
Balance, beginning of period			$ 17,363
Net loss	$ (4)	$ (674)	(1,700)	$ (1,046)
Change in unrealized net capital gains and losses	(667)	(789)	(257)	(3,527)
Change in discount rate for reserve for future policy benefits	30	52	29	232
Balance, end of period	14,447	17,571	14,447	17,571
Total Allstate shareholders’ equity	14,593	17,683	14,593	17,683	$ 17,488
Total equity	14,447	17,571	14,447	17,571	17,363
Retained income
Increase (decrease) in equity
Balance, beginning of period	48,766	52,412	50,970	53,288
Net loss	(5)	(659)	(1,677)	(1,012)
Balance, end of period	48,491	51,499	48,491	51,499
Total equity	48,491	51,499	48,491	51,499	50,970
Accumulated other comprehensive income (loss)
Increase (decrease) in equity
Balance, beginning of period	(1,914)	(2,209)	(2,392)	426
Change in unrealized net capital gains and losses	(667)	(789)	(257)	(3,527)
Change in discount rate for reserve for future policy benefits	30	52		232
Balance, end of period	(2,570)	(3,042)	(2,570)	(3,042)
Total equity	$ (2,570)	(3,042)	(2,570)	(3,042)	(2,392)
As reported
Increase (decrease) in equity
Balance, beginning of period			17,350
Net loss		(683)		(1,061)
Change in unrealized net capital gains and losses		(789)		(3,525)
Change in discount rate for reserve for future policy benefits		0		0
Balance, end of period		17,561		17,561
Total Allstate shareholders’ equity		17,673		17,673	17,475
Total equity		17,561		17,561	17,350
As reported | Retained income
Increase (decrease) in equity
Balance, beginning of period		52,412		53,294
Net loss		(668)		(1,027)
Balance, end of period		51,490		51,490
Total equity		51,490		51,490
As reported | Accumulated other comprehensive income (loss)
Increase (decrease) in equity
Balance, beginning of period		(2,158)		655
Change in unrealized net capital gains and losses		(789)		(3,525)
Change in discount rate for reserve for future policy benefits		0		0
Balance, end of period		(3,043)		(3,043)
Total equity		(3,043)		(3,043)
Impact of change
Increase (decrease) in equity
Balance, beginning of period			$ 13
Net loss		9		15
Change in unrealized net capital gains and losses		0		(2)
Change in discount rate for reserve for future policy benefits		52		232
Balance, end of period		10		10
Total Allstate shareholders’ equity		10		10	13
Total equity		10		10	$ 13
Impact of change | Retained income
Increase (decrease) in equity
Balance, beginning of period		0		(6)
Net loss		9		15
Balance, end of period		9		9
Total equity		9		9
Impact of change | Accumulated other comprehensive income (loss)
Increase (decrease) in equity
Balance, beginning of period		(51)		(229)
Change in unrealized net capital gains and losses		0		(2)
Change in discount rate for reserve for future policy benefits		52		232
Balance, end of period		1		1
Total equity		$ 1		$ 1