General - Schedule of condensed consolidated statements of shareholders’ equity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Increase (decrease) in equity
Balance, beginning of period	$ 17,363
Net income	(321)	$ 650
Unrealized net capital gains and losses	682	(1,594)
Change in discount rate for reserve for future policy benefits	(9)	95
Total Allstate shareholders’ equity	17,494	23,075	$ 17,488
Balance, end of period	17,373	23,001
Total equity	17,373	23,001	17,363
Retained income
Increase (decrease) in equity
Balance, beginning of period	50,970	53,288
Net income	(320)	660
Balance, end of period	50,388	53,686
Total equity	50,388	53,686	50,970
Accumulated other comprehensive income
Increase (decrease) in equity
Balance, beginning of period	(2,392)	426
Unrealized net capital gains and losses	682	(1,594)
Change in discount rate for reserve for future policy benefits	(9)	95
Balance, end of period	(1,673)	(1,088)
Total equity	(1,673)	(1,088)	(2,392)
As reported
Increase (decrease) in equity
Balance, beginning of period	17,350
Net income		646
Unrealized net capital gains and losses		(1,593)
Change in discount rate for reserve for future policy benefits		0
Total Allstate shareholders’ equity		23,212	17,475
Balance, end of period		23,138
Total equity		23,138	17,350
As reported | Retained income
Increase (decrease) in equity
Balance, beginning of period		53,294
Net income		656
Balance, end of period		53,688
Total equity		53,688
As reported | Accumulated other comprehensive income
Increase (decrease) in equity
Balance, beginning of period		655
Unrealized net capital gains and losses		(1,593)
Change in discount rate for reserve for future policy benefits		0
Balance, end of period		(953)
Total equity		(953)
Impact of change
Increase (decrease) in equity
Balance, beginning of period	$ 13
Net income		4
Unrealized net capital gains and losses		(1)
Change in discount rate for reserve for future policy benefits		95
Total Allstate shareholders’ equity		(137)	13
Balance, end of period		(137)
Total equity		(137)	$ 13
Impact of change | Retained income
Increase (decrease) in equity
Balance, beginning of period		(6)
Net income		4
Balance, end of period		(2)
Total equity		(2)
Impact of change | Accumulated other comprehensive income
Increase (decrease) in equity
Balance, beginning of period		(229)
Unrealized net capital gains and losses		(1)
Change in discount rate for reserve for future policy benefits		95
Balance, end of period		(135)
Total equity		$ (135)