Schedule II - Condensed Financial Information of Registrant - Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Investment income, less investment expense									$ 2,853	$ 3,159	$ 3,240
Realized capital gains (losses)	$ 4								1,356	1,885	(877)
Total revenues	12,018	$ 11,500	$ 11,197	$ 10,076	$ 11,472	$ 11,069	$ 11,144	$ 10,990	44,791	44,675	39,815
Expenses
Interest expense									318	327	332
Pension and other postretirement remeasurement (gains) losses									(51)	114	468
Other operating expenses									5,732	5,690	5,594
Total costs and expenses									37,836	38,592	37,193
Income tax expense (benefit)									1,383	1,242	468
Net income									5,576	4,847	2,160
Preferred stock dividends									115	169	148
Net income (loss) applicable to common shareholders	$ 2,598	$ 1,126	$ 1,224	$ 513	$ 1,707	$ 889	$ 821	$ 1,261	5,461	4,678	2,012
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									1,293	1,889	(754)
Unrealized foreign currency translation adjustments									52	(10)	(48)
Unamortized pension and other postretirement prior service credit									9	(47)	(59)
Other comprehensive income (loss), after-tax									1,354	1,832	(861)
Comprehensive income									6,930	6,679	1,299
Allstate Corporation
Revenues
Investment income, less investment expense									12	35	25
Realized capital gains (losses)									33	9	(10)
Other income									0	41	3
Total revenues									45	85	18
Expenses
Interest expense									328	355	337
Pension and other postretirement remeasurement (gains) losses									(73)	103	454
Pension and other postretirement benefit									(168)	(122)	(116)
Other operating expenses									73	49	50
Total costs and expenses									160	385	725
Loss from operations before income tax benefit and equity in net income of subsidiaries									(115)	(300)	(707)
Income tax expense (benefit)									(26)	(75)	(136)
Loss before equity in net income of subsidiaries									(89)	(225)	(571)
Equity in net income of subsidiaries									5,665	5,072	2,731
Net income									5,576	4,847	2,160
Preferred stock dividends									115	169	148
Net income (loss) applicable to common shareholders									5,461	4,678	2,012
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									1,293	1,889	(754)
Unrealized foreign currency translation adjustments									52	(10)	(48)
Unamortized pension and other postretirement prior service credit									9	(47)	(59)
Other comprehensive income (loss), after-tax									1,354	1,832	(861)
Comprehensive income									$ 6,930	$ 6,679	$ 1,299