Schedule II - Condensed Financial Information of Registrant - Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Net investment income									$ 3,401	$ 3,042	$ 3,156
Realized capital gains and losses									445	(90)	30
Total revenues	$ 9,843	$ 9,660	$ 9,587	$ 9,434	$ 9,278	$ 9,221	$ 9,164	$ 8,871	38,524	36,534	35,653
Expenses
Interest expense									335	295	292
Other operating expenses									4,658	4,106	4,081
Total costs and expenses									34,553	33,785	32,374
Income tax expense (benefit)									802	877	1,111
Net income									3,189	1,877	2,171
Preferred stock dividends									116	116	116
Net income applicable to common shareholders	$ 1,220	$ 637	$ 550	$ 666	$ 811	$ 491	$ 242	$ 217	3,073	1,761	2,055
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									319	433	(1,306)
Unrealized foreign currency translation adjustments									47	10	(58)
Unrecognized pension and other postretirement benefit cost									307	(104)	48
Other comprehensive income (loss), after-tax									673	339	(1,316)
Comprehensive income									3,862	2,216	855
Allstate Corporation
Revenues
Net investment income									10	11	8
Realized capital gains and losses									(2)	2	0
Other income									36	55	66
Total revenues									44	68	74
Expenses
Interest expense									334	295	292
Pension and other postretirement benefit expense									119	10	(15)
Other operating expenses									50	28	34
Total costs and expenses									503	333	311
Loss from operations before income tax benefit and equity in net income of subsidiaries									(459)	(265)	(237)
Income tax expense (benefit)									(92)	(115)	(108)
Loss before equity in net income of subsidiaries									(367)	(150)	(129)
Equity in net income of subsidiaries									3,556	2,027	2,300
Net income									3,189	1,877	2,171
Preferred stock dividends									116	116	116
Net income applicable to common shareholders									3,073	1,761	2,055
Other comprehensive income (loss), after-tax
Unrealized net capital gains and losses									319	433	(1,306)
Unrealized foreign currency translation adjustments									47	10	(58)
Unrecognized pension and other postretirement benefit cost									307	(104)	48
Other comprehensive income (loss), after-tax									673	339	(1,316)
Comprehensive income									$ 3,862	$ 2,216	$ 855