Schedule II - Condensed Financial Information of Registrant - Financial Position (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets
Fixed income securities	$ 42,136	$ 42,565
Short-term investments	4,009	6,807
Cash	763	311
Total assets	99,440	125,987
Liabilities
Long-term debt	7,976	7,825
Total liabilities	74,313	95,770
Shareholders’ equity
Preferred stock and additional capital paid-in, $1 par value, 25 million shares authorized, 81.0 thousand shares issued and outstanding, $2,025 aggregate liquidation preference	1,970	1,970
Common stock, $.01 par value, 2.0 billion shares authorized and 900 million issued, 281 million and 304 million shares outstanding	9	9
Additional capital paid-in	3,722	3,498
Retained income	53,294	52,767
Treasury Stock, Value	(34,471)	(31,331)
Accumulated other comprehensive income:
Unrealized net capital gains and losses	598	3,180
Unrealized foreign currency translation adjustments	(15)	(7)
Unamortized pension and other postretirement prior service credit	72	131
Total accumulated other comprehensive income	655	3,304
Total Allstate shareholders’ equity	25,179	30,217	$ 25,998
Total liabilities and equity	99,440	125,987
Additional balance sheet disclosures:
Amortized cost, net	41,376	40,034
Other short term Investments, amortized cost	$ 4,009	$ 6,807
Preferred stock, par or stated value per share (in USD per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	81,000	81,000
Preferred stock, shares outstanding (in shares)	81,000	81,000
Preferred Stock, liquidation preference	$ 2,025	$ 2,025
Common stock, par or stated value per share (in USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	2,000,000,000	2,000,000,000
Common stock, shares, issued (in shares)	900,000,000	900,000,000
Common stock, shares, outstanding (in shares)	281,000,000	304,000,000
Treasury stock, shares (in shares)	619,000,000	596,000,000
Allstate Corporation
Assets
Investment in subsidiaries	$ 32,058	$ 35,603
Fixed income securities	1,718	0
Short-term investments	297	4,479
Cash	1	0	$ 2	$ 0
Receivable from subsidiaries	504	524
Deferred income taxes	22	187
Other assets	222	87
Total assets	34,822	40,880
Liabilities
Long-term debt	7,581	7,825
Pension and other postretirement benefit obligations	211	874
Deferred compensation	383	351
Payable to subsidiaries	0	0
Notes due to subsidiaries	1,000	1,250
Dividends payable to shareholders	269	201
Other liabilities	199	162
Total liabilities	9,643	10,663
Shareholders’ equity
Preferred stock and additional capital paid-in, $1 par value, 25 million shares authorized, 81.0 thousand shares issued and outstanding, $2,025 aggregate liquidation preference	1,970	1,970
Common stock, $.01 par value, 2.0 billion shares authorized and 900 million issued, 281 million and 304 million shares outstanding	9	9
Additional capital paid-in	3,722	3,498
Retained income	53,294	52,767
Treasury Stock, Value	(34,471)	(31,331)
Accumulated other comprehensive income:
Unrealized net capital gains and losses	598	3,180
Unrealized foreign currency translation adjustments	(15)	(7)
Unamortized pension and other postretirement prior service credit	72	131
Total accumulated other comprehensive income	655	3,304
Total Allstate shareholders’ equity	25,179	30,217
Total liabilities and equity	34,822	40,880
Additional balance sheet disclosures:
Amortized cost, net	1,708	0
Other short term Investments, amortized cost	$ 297	$ 4,479
Preferred stock, par or stated value per share (in USD per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	81,000
Preferred stock, shares outstanding (in shares)	81,000
Preferred Stock, liquidation preference	$ 2,025
Common stock, par or stated value per share (in USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	2,000,000,000	2,000,000,000
Common stock, shares, issued (in shares)	900,000,000	900,000,000
Common stock, shares, outstanding (in shares)	281,000,000	304,000,000
Treasury stock, shares (in shares)	619,000,000	596,000,000