Schedule II - Condensed Financial Information of Registrant - Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues
Investment income, less investment expense									$ 3,293	$ 1,590	$ 1,728
Net gains (losses) on investments and derivatives									1,279	1,356	1,885
Total revenues	$ 13,011	$ 12,480	$ 12,646	$ 12,451	$ 10,962	$ 10,678	$ 10,403	$ 9,866	50,588	41,909	41,541
Expenses
Interest expense									330	318	327
Pension and other postretirement remeasurement (gains) losses									(644)	(51)	114
Other operating expenses									7,260	5,494	5,422
Total costs and expenses									44,140	35,107	36,098
Income tax expense (benefit)									1,289	1,373	1,116
Net income attributable to Allstate									1,599	5,576	4,847
Less: Preferred stock dividends									114	115	169
Net income (loss) applicable to common shareholders	$ 790	$ 508	$ 1,595	$ (1,408)	$ 2,598	$ 1,126	$ 1,224	$ 513	1,485	5,461	4,678
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									(2,582)	1,293	1,889
Unrealized foreign currency translation adjustments									(8)	52	(10)
Unamortized pension and other postretirement prior service credit									(59)	9	(47)
Other comprehensive income (loss), after-tax									(2,649)	1,354	1,832
Comprehensive income									(1,047)	6,930	6,679
Allstate Corporation
Revenues
Investment income, less investment expense									13	12	35
Net gains (losses) on investments and derivatives									12	33	9
Other income									0	0	41
Total revenues									25	45	85
Expenses
Interest expense									328	328	355
Pension and other postretirement remeasurement (gains) losses									(611)	(73)	103
Pension and other postretirement (benefit) expense									(218)	(168)	(122)
Other operating expenses									71	73	49
Total costs and expenses									(430)	160	385
Gain (loss) from operations before income tax benefit and equity in net income of subsidiaries									455	(115)	(300)
Income tax expense (benefit)									93	(26)	(75)
Gain (loss) before equity in net income of subsidiaries									362	(89)	(225)
Equity in net income of subsidiaries									1,237	5,665	5,072
Net income attributable to Allstate									1,599	5,576	4,847
Less: Preferred stock dividends									114	115	169
Net income (loss) applicable to common shareholders									1,485	5,461	4,678
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									(2,582)	1,293	1,889
Unrealized foreign currency translation adjustments									(8)	52	(10)
Unamortized pension and other postretirement prior service credit									(59)	9	(47)
Other comprehensive income (loss), after-tax									(2,649)	1,354	1,832
Comprehensive income									$ (1,050)	$ 6,930	$ 6,679