Reporting Segments (Details 3) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information
Net investment income									$ 3,042	$ 3,156	$ 3,459
Net income applicable to common shareholders	$ 811	$ 491	$ 242	$ 217	$ 460	$ 621	$ 326	$ 648	1,761	2,055	2,746
Life and annuity premiums and contract charges									2,275	2,158	2,157
Restructuring and related charges									(30)	(39)	(18)
Total income tax expense									877	1,111	1,386
Accounting Standards Update 2014-01
Segment Reporting Information
Total income tax expense										45
Allstate Protection
Segment Reporting Information
Underwriting income									1,317	1,614	1,887
Discontinued Lines and Coverages
Segment Reporting Information
Underwriting income									(107)	(55)	(115)
Property-Liability
Segment Reporting Information
Underwriting income									1,210	1,559	1,772
Net investment income									1,266	1,237	1,301
Income tax benefit (expense) on operations									(812)	(952)	(1,040)
Realized capital gains and losses, after-tax									0	(154)	357
Gain (loss) on disposition of operations, after-tax									0	0	37
Net income applicable to common shareholders									1,664	1,690	2,427
Total income tax expense									806	869	1,211
Property-Liability | Accounting Standards Update 2014-01
Segment Reporting Information
Total income tax expense									28
Allstate Financial
Segment Reporting Information
Net investment income									1,734	1,884	2,131
Income tax benefit (expense) on operations									(206)	(241)	(294)
Realized capital gains and losses, after-tax									(54)	173	94
Gain (loss) on disposition of operations, after-tax									3	2	(53)
Net income applicable to common shareholders									391	663	631
Life and annuity premiums and contract charges									2,275	2,158	2,157
Periodic settlements and accruals on non-hedge derivative instruments									0	0	(1)
Contract benefits and interest credited to contractholder funds									(2,580)	(2,563)	(2,663)
Operating costs and expenses and amortization of deferred policy acquisition costs									(774)	(729)	(721)
Restructuring and related charges									(1)	0	(2)
Operating Income (loss)									448	509	607
Valuation changes on embedded derivatives that are not hedged, after-tax									(2)	(1)	(15)
DAC and DSI amortization related to realized capital gains and losses and valuation changes on embedded derivatives that are not hedged, after-tax									(4)	(3)	(3)
Reclassification of periodic settlements and accruals on non-hedge derivative instruments, after-tax									0	0	1
Change in accounting for investments in qualified affordable housing projects, after-tax									0	(17)	0
Total income tax expense									178	351	299
Corporate and Other
Segment Reporting Information
Net investment income									42	35	27
Income tax benefit (expense) on operations									106	109	124
Realized capital gains and losses, after-tax									(2)	0	0
Net income applicable to common shareholders									(294)	(298)	(312)
Operating Income (loss)									(292)	(298)	(312)
Service fees									4	3	5
Operating costs and expenses									(328)	(329)	(364)
Preferred stock dividends									(116)	(116)	(104)
Total income tax expense									$ 107	$ 109	$ 124