Reporting Segments (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information
Property-liability insurance premiums									$ 26,737	$ 25,942	$ 25,957
Life and annuity premiums and contract charges									2,241	2,238	2,168
Net investment income									4,010	3,971	4,102
Realized capital gains and losses									327	503	(827)
Consolidated revenues	8,547	8,128	8,278	8,362	8,236	8,242	8,081	8,095	33,315	32,654	31,400
Property-Liability
Segment Reporting Information
Property-liability insurance premiums									26,737	25,942	25,957
Net investment income									1,326	1,201	1,189
Realized capital gains and losses									335	85	(321)
Consolidated revenues									28,398	27,228	26,825
Property-Liability | Total auto
Segment Reporting Information
Property-liability insurance premiums									17,928	17,299	17,435
Property-Liability | Standard auto
Segment Reporting Information
Property-liability insurance premiums									17,213	16,500	16,530
Property-Liability | Non-standard auto
Segment Reporting Information
Property-liability insurance premiums									715	799	905
Property-Liability | Homeowners
Segment Reporting Information
Property-liability insurance premiums									6,359	6,200	6,078
Property-Liability | Other personal lines
Segment Reporting Information
Property-liability insurance premiums									2,450	2,443	2,442
Allstate Protection
Segment Reporting Information
Property-liability insurance premiums									26,737	25,942	25,955
Discontinued Lines and Coverages
Segment Reporting Information
Property-liability insurance premiums											2
Corporate and Other
Segment Reporting Information
Service fees									4	7	11
Net investment income									37	54	60
Realized capital gains and losses									5	30	11
Total Corporate and Other before reclassification of service fees									46	91	82
Reclassification of service fees									(4)	(7)	(11)
Consolidated revenues									42	84	71
Allstate Financial
Segment Reporting Information
Life and annuity premiums and contract charges									2,241	2,238	2,168
Net investment income									2,647	2,716	2,853
Realized capital gains and losses									(13)	388	(517)
Consolidated revenues									4,875	5,342	4,504
Allstate Financial | Total life and annuity premiums
Segment Reporting Information
Life and annuity premiums and contract charges									1,168	1,190	1,138
Allstate Financial | Traditional life insurance
Segment Reporting Information
Life and annuity premiums and contract charges									470	441	420
Allstate Financial | Immediate annuities with life contingencies
Segment Reporting Information
Life and annuity premiums and contract charges									45	106	97
Allstate Financial | Accident and health insurance:
Segment Reporting Information
Life and annuity premiums and contract charges									653	643	621
Allstate Financial | Total contract charges
Segment Reporting Information
Life and annuity premiums and contract charges									1,073	1,048	1,030
Allstate Financial | Interest-sensitive life insurance
Segment Reporting Information
Life and annuity premiums and contract charges									1,055	1,015	991
Allstate Financial | Fixed annuities
Segment Reporting Information
Life and annuity premiums and contract charges									$ 18	$ 33	$ 39