General - Schedule of condensed consolidated statements of shareholders’ equity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Increase (decrease) in equity
Balance, beginning of period			$ 17,363
Net loss	$ (1,375)	$ (1,022)	(1,696)	$ (372)
Unrealized net capital gains and losses	(272)	(1,144)	410	(2,738)
Change in discount rate for reserve for future policy benefits	8	85	(1)	180
Total Allstate shareholders’ equity	15,517	20,064	15,517	20,064	$ 17,488
Balance, end of period	15,372	19,973	15,372	19,973
Total equity	15,372	19,973	15,372	19,973	17,363
Retained income
Increase (decrease) in equity
Balance, beginning of period	50,388	53,686	50,970	53,288
Net loss	(1,352)	(1,013)	(1,672)	(353)
Balance, end of period	48,766	52,412	48,766	52,412
Total equity	48,766	52,412	48,766	52,412	50,970
Accumulated other comprehensive income (loss)
Increase (decrease) in equity
Balance, beginning of period	(1,673)	(1,088)	(2,392)	426
Unrealized net capital gains and losses	(272)	(1,144)	410	(2,738)
Change in discount rate for reserve for future policy benefits	8	85		180
Balance, end of period	(1,914)	(2,209)	(1,914)	(2,209)
Total equity	$ (1,914)	(2,209)	(1,914)	(2,209)	(2,392)
As reported
Increase (decrease) in equity
Balance, beginning of period			17,350
Net loss		(1,024)		(378)
Unrealized net capital gains and losses		(1,143)		(2,736)
Change in discount rate for reserve for future policy benefits		0		0
Total Allstate shareholders’ equity		20,115		20,115	17,475
Balance, end of period		20,024		20,024
Total equity		20,024		20,024	17,350
As reported | Retained income
Increase (decrease) in equity
Balance, beginning of period		53,688		53,294
Net loss		(1,015)		(359)
Balance, end of period		52,412		52,412
Total equity		52,412		52,412
As reported | Accumulated other comprehensive income (loss)
Increase (decrease) in equity
Balance, beginning of period		(953)		655
Unrealized net capital gains and losses		(1,143)		(2,736)
Change in discount rate for reserve for future policy benefits		0		0
Balance, end of period		(2,158)		(2,158)
Total equity		(2,158)		(2,158)
Impact of change
Increase (decrease) in equity
Balance, beginning of period			$ 13
Net loss		2		6
Unrealized net capital gains and losses		(1)		(2)
Change in discount rate for reserve for future policy benefits		85		180
Total Allstate shareholders’ equity		(51)		(51)	13
Balance, end of period		(51)		(51)
Total equity		(51)		(51)	$ 13
Impact of change | Retained income
Increase (decrease) in equity
Balance, beginning of period		(2)		(6)
Net loss		2		6
Balance, end of period		0		0
Total equity		0		0
Impact of change | Accumulated other comprehensive income (loss)
Increase (decrease) in equity
Balance, beginning of period		(135)		(229)
Unrealized net capital gains and losses		(1)		(2)
Change in discount rate for reserve for future policy benefits		85		180
Balance, end of period		(51)		(51)
Total equity		$ (51)		$ (51)