Condensed Consolidated Statements of Shareholders’ Equity (unaudited) - USD ($) $ in Millions	Total	Preferred Stock	Preferred stock additional capital paid-in	Common stock par value	Common stock additional capital paid-in	Retained income	Retained income Cumulative effect of change in accounting principle	Treasury stock	Accumulated other comprehensive income (loss)	Noncontrolling Interest
Increase (decrease) in equity
Total equity			$ 2,248		$ 3,463	$ 48,074	$ (88)	$ (29,746)	$ 1,950	$ 0
Balance, beginning of period at Dec. 31, 2019			2,248		3,463	48,074	(88)	(29,746)	1,950	0
Increase (decrease) in equity
Acquisition			0							0
Preferred stock redemption			(278)
Forward contract on accelerated share repurchase agreement					(38)
Equity incentive plans activity					28
Net income	$ 2,952					2,952				0
Dividends on common stock (declared per share of $0.81, $0.54, $2.43 and $1.62)						(513)
Dividends on preferred stock						(89)
Shares acquired								(1,700)
Shares reissued under equity incentive plans, net								108
Change in unrealized net capital gains and losses	857								857	0
Change in unrealized foreign currency translation adjustments	(5)								(5)
Change in unamortized pension and other postretirement prior service credit	31								31
Balance, end of period at Sep. 30, 2020	27,263	$ 0	1,970	$ 9	3,453	50,336		(31,338)	2,833	0
Increase (decrease) in equity
Total equity			1,970		3,541	49,380	0	(30,542)	2,628	0
Balance, beginning of period at Jun. 30, 2020			1,970		3,541	49,380	0	(30,542)	2,628	0
Increase (decrease) in equity
Acquisition			0							0
Preferred stock redemption			0
Forward contract on accelerated share repurchase agreement					(113)
Equity incentive plans activity					25
Net income	1,153					1,153				0
Dividends on common stock (declared per share of $0.81, $0.54, $2.43 and $1.62)						(170)
Dividends on preferred stock						(27)
Shares acquired								(798)
Shares reissued under equity incentive plans, net								2
Change in unrealized net capital gains and losses	142								142	0
Change in unrealized foreign currency translation adjustments	25								25
Change in unamortized pension and other postretirement prior service credit	38								38
Balance, end of period at Sep. 30, 2020	27,263	0	1,970	9	3,453	50,336		(31,338)	2,833	0
Increase (decrease) in equity
Total Allstate shareholders’ equity	27,263
Total equity	27,263	0	1,970	9	3,453	50,336		(31,338)	2,833	0
Total Allstate shareholders’ equity	30,217
Total equity	30,217		1,970		3,498	52,767	0	(31,331)	3,304	0
Balance, beginning of period at Dec. 31, 2020	30,217		1,970		3,498	52,767	0	(31,331)	3,304	0
Increase (decrease) in equity
Acquisition			450							(1)
Preferred stock redemption			(450)
Forward contract on accelerated share repurchase agreement					113
Equity incentive plans activity					89
Net income	775					782				(7)
Dividends on common stock (declared per share of $0.81, $0.54, $2.43 and $1.62)						(726)
Dividends on preferred stock						(87)
Shares acquired								(2,390)
Shares reissued under equity incentive plans, net								117
Change in unrealized net capital gains and losses	(1,352)								(1,352)	(14)
Change in unrealized foreign currency translation adjustments	10								10
Change in unamortized pension and other postretirement prior service credit	(44)								(44)
Balance, end of period at Sep. 30, 2021	26,707	0	1,970	9	3,700	52,736		(33,604)	1,918	(22)
Increase (decrease) in equity
Total equity			2,170		3,668	52,464	0	(32,394)	2,290	(15)
Balance, beginning of period at Jun. 30, 2021			2,170		3,668	52,464	$ 0	(32,394)	2,290	(15)
Increase (decrease) in equity
Acquisition			0							0
Preferred stock redemption			(200)
Forward contract on accelerated share repurchase agreement					0
Equity incentive plans activity					32
Net income	531					538				(7)
Dividends on common stock (declared per share of $0.81, $0.54, $2.43 and $1.62)						(236)
Dividends on preferred stock						(30)
Shares acquired								(1,227)
Shares reissued under equity incentive plans, net								17
Change in unrealized net capital gains and losses	(336)								(336)	0
Change in unrealized foreign currency translation adjustments	(21)								(21)
Change in unamortized pension and other postretirement prior service credit	(15)								(15)
Balance, end of period at Sep. 30, 2021	26,707	0	1,970	9	3,700	52,736		(33,604)	1,918	(22)
Increase (decrease) in equity
Total Allstate shareholders’ equity	26,729
Total equity	$ 26,707	$ 0	$ 1,970	$ 9	$ 3,700	$ 52,736		$ (33,604)	$ 1,918	$ (22)