Schedule II - Condensed Financial Information of Registrant - Cash Flows (Details) - USD ($) $ in Millions		12 Months Ended
	Feb. 02, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net income		$ 1,599	$ 5,576	$ 4,847
Adjustments to reconcile net income to net cash provided by operating activities:
Net gains (losses) on investments and derivatives		(1,279)	(1,356)	(1,885)
Pension and other postretirement remeasurement (gains) losses		(644)	(51)	114
Changes in:
Net cash provided by operating activities		5,116	5,491	5,129
Cash flows from investing activities
Change in short-term and other investments, net		4,017	(3,871)	(725)
Acquisition of operations, net of cash acquired		(3,593)	1	(18)
Net cash provided by (used in) investing activities		510	(3,441)	(2,807)
Cash flows from financing activities
Proceeds from issuance of long-term debt		0	1,189	491
Redemption of preferred stock	$ (250)
Redemption and repayment of long-term debt		(436)	0	(317)
Proceeds from issuance of preferred stock		0	0	(1,132)
Dividends paid on common stock		(885)	(668)	(653)
Dividends paid on preferred stock		(114)	(108)	(134)
Treasury stock purchases		(3,120)	(1,737)	(1,735)
Shares reissued under equity incentive plans, net		114	63	120
Other		(35)	41	129
Net cash used in financing activities		(5,240)	(2,011)	(2,483)
Cash at beginning of year		311
Cash at end of year		763	311
Allstate Corporation
Cash flows from operating activities
Net income		1,599	5,576	4,847
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in net income of subsidiaries		(1,237)	(5,665)	(5,072)
Dividends received from subsidiaries		5,112	4,157	2,434
Net gains (losses) on investments and derivatives		(12)	(33)	(9)
Pension and other postretirement remeasurement (gains) losses		(611)	(73)	103
Changes in:
Pension and other postretirement benefits		(218)	(168)	(122)
Income taxes		177	54	13
Operating assets and liabilities		158	110	111
Net cash provided by operating activities		4,968	3,958	2,305
Cash flows from investing activities
Proceeds from sales of investments		1,743	1,251	1,094
Investment purchases		(2,673)	(402)	(892)
Investment collections		38	16	65
Capital contribution or return of capital from subsidiaries		383	251	43
Change in short-term and other investments, net		4,182	(3,777)	(417)
Acquisition of operations, net of cash acquired		(4,144)	0	0
Net cash provided by (used in) investing activities		(471)	(2,661)	(107)
Cash flows from financing activities
Proceeds from borrowings from subsidiaries		2,200	1,250	1,000
Repayment of notes due to subsidiaries		(2,450)	(1,000)	(1,250)
Proceeds from issuance of long-term debt		0	1,189	491
Redemption of preferred stock		0	(288)	(1,132)
Redemption and repayment of long-term debt		(250)	0	(317)
Proceeds from issuance of preferred stock		0	0	1,414
Dividends paid on common stock		(885)	(668)	(653)
Dividends paid on preferred stock		(105)	(108)	(134)
Treasury stock purchases		(3,120)	(1,737)	(1,735)
Shares reissued under equity incentive plans, net		114	63	120
Other		0	0	0
Net cash used in financing activities		(4,496)	(1,299)	(2,196)
Net increase (decrease) in cash		1	(2)	2
Cash at beginning of year		0	2	0
Cash at end of year		$ 1	$ 0	$ 2