Reporting Segments (Details 3) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information
Life and annuity premiums and contract charges									$ 2,158	$ 2,157	$ 2,352
Net investment income									3,156	3,459	3,943
Restructuring and related charges									(39)	(18)	(70)
Net income applicable to common shareholders	$ 460	$ 621	$ 326	$ 648	$ 795	$ 750	$ 614	$ 587	2,055	2,746	2,263
Amortization of DAC									4,364	4,135	4,002
Total income tax expense									1,111	1,386	1,116
Property-Liability
Segment Reporting Information
Underwriting income									1,559	1,772	2,218
Net investment income									1,237	1,301	1,375
Income tax expense on operations									(952)	(1,040)	(1,177)
Realized capital gains and losses, after-tax									(154)	357	339
Gain (loss) on disposition of operations, after-tax									0	37	(1)
Net income applicable to common shareholders									1,690	2,427	2,754
Amortization of DAC									4,102	3,875	3,674
Total income tax expense									869	1,211	1,357
Allstate Protection
Segment Reporting Information
Underwriting income									1,614	1,887	2,361
Discontinued Lines and Coverages
Segment Reporting Information
Underwriting income									(55)	(115)	(143)
Allstate Financial
Segment Reporting Information
Life and annuity premiums and contract charges									2,158	2,157	2,352
Net investment income									1,884	2,131	2,538
Periodic settlements and accruals on non-hedge derivative instruments									0	(1)	17
Contract benefits and interest credited to contractholder funds									(2,563)	(2,663)	(3,171)
Operating costs and expenses and amortization of deferred policy acquisition costs									(729)	(721)	(895)
Restructuring and related charges									0	(2)	(7)
Income tax expense on operations									(241)	(294)	(246)
Operating Income (loss)									509	607	588
Realized capital gains and losses, after-tax									173	94	46
Valuation changes on embedded derivatives that are not hedged, after-tax									(1)	(15)	(16)
DAC and DSI amortization related to realized capital gains and losses and valuation changes on embedded derivatives that are not hedged, after-tax									(3)	(3)	(5)
DAC and DSI unlocking related to realized capital gains and losses, after-tax									0	0	7
Reclassification of periodic settlements and accruals on non-hedge derivative instruments, after-tax									0	1	(11)
Gain (loss) on disposition of operations, after-tax									2	(53)	(514)
Change in accounting for investments in qualified affordable housing projects, after-tax									(17)	0	0
Net income applicable to common shareholders									663	631	95
Amortization of DAC									262	260	328
Total income tax expense									351	299	87
Corporate and Other
Segment Reporting Information
Service fees									3	5	9
Net investment income									35	27	30
Operating costs and expenses									(329)	(364)	(627)
Income tax expense on operations									109	124	220
Preferred stock dividends									(116)	(104)	(17)
Operating Income (loss)									(298)	(312)	(385)
Realized capital gains and losses, after-tax									0	0	0
Loss on extinguishment of debt, after-tax									0	0	(319)
Postretirement benefits curtailment gain, after-tax									0	0	118
Net income applicable to common shareholders									(298)	(312)	(586)
Total income tax expense									(109)	$ (124)	$ (328)
Accounting Standards Update 2014-01
Segment Reporting Information
Total income tax expense				$ 45
Accounting Standards Update 2014-01 | Property-Liability
Segment Reporting Information
Total income tax expense									$ 28