Schedule II - Condensed Financial Information of Registrant - Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues
Net investment income									$ 3,159	$ 3,240	$ 3,401
Realized capital gains and losses									1,885	(877)	445
Total revenues	$ 11,472	$ 11,069	$ 11,144	$ 10,990	$ 9,481	$ 10,465	$ 10,099	$ 9,770	44,675	39,815	39,407
Expenses
Interest expense									327	332	335
Other operating expenses									5,690	5,594	5,196
Total costs and expenses									38,592	37,193	34,878
Income tax expense (benefit)									1,242	468	995
Net income									4,847	2,160	3,554
Preferred stock dividends									169	148	116
Net income applicable to common shareholders	$ 1,707	$ 889	$ 821	$ 1,261	$ (585)	$ 942	$ 678	$ 977	4,678	2,012	3,438
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									1,889	(754)	319
Unrealized foreign currency translation adjustments									(10)	(48)	45
Unamortized pension and other postretirement prior service credit									(47)	(59)	(52)
Other comprehensive income (loss), after-tax									1,832	(861)	312
Comprehensive income									6,679	1,299	3,866
Allstate Corporation
Revenues
Net investment income									35	25	10
Realized capital gains and losses									9	(10)	(2)
Other income									41	3	36
Total revenues									85	18	44
Expenses
Interest expense									355	337	334
Pension and other postretirement remeasurement gains and losses									103	454	(219)
Pension and other postretirement benefit expense									(122)	(116)	(224)
Other operating expenses									49	50	50
Total costs and expenses									385	725	(59)
(Loss) gain from operations before income tax benefit and equity in net income of subsidiaries									(300)	(707)	103
Income tax expense (benefit)									(75)	(136)	105
Loss before equity in net income of subsidiaries									(225)	(571)	(2)
Equity in net income of subsidiaries									5,072	2,731	3,556
Net income									4,847	2,160	3,554
Preferred stock dividends									169	148	116
Net income applicable to common shareholders									4,678	2,012	3,438
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									1,889	(754)	319
Unrealized foreign currency translation adjustments									(10)	(48)	45
Unamortized pension and other postretirement prior service credit									(47)	(59)	(52)
Other comprehensive income (loss), after-tax									1,832	(861)	312
Comprehensive income									$ 6,679	$ 1,299	$ 3,866