Reporting Segments (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Property-Liability
Net investment income	$ 762	$ 789	$ 1,493	$ 1,639
Allstate Financial
Life and annuity premiums and contract charges	564	536	1,130	1,073
Restructuring and related charges	(11)	(19)	(16)	(23)
Corporate and Other
Net income applicable to common shareholders	242	326	459	974
Income tax expense	105	171	214	575
Allstate Protection
Property-Liability
Underwriting income	(64)	(8)	63	461
Discontinued Lines and Coverages
Property-Liability
Underwriting income	(2)	(2)	(4)	(4)
Property-Liability
Property-Liability
Underwriting income	(66)	(10)	59	457
Net investment income	316	292	618	650
Income tax (expense) benefit on operations	(70)	(92)	(211)	(397)
Realized capital gains and losses, after-tax	18	31	(46)	49
Allstate Financial
Realized capital gains and losses, after-tax	18	31	(46)	49
Gain (loss) on disposition of operations, after-tax	0	1	0	1
Corporate and Other
Realized capital gains and losses, after-tax	18	31	(46)	49
Net income applicable to common shareholders	198	222	420	760
Allstate Financial
Property-Liability
Net investment income	435	489	854	973
Income tax (expense) benefit on operations	(56)	(67)	(104)	(129)
Realized capital gains and losses, after-tax	0	38	(32)	110
Allstate Financial
Life and annuity premiums and contract charges	564	536	1,130	1,073
Contract benefits and interest credited to contractholder funds	(633)	(637)	(1,272)	(1,270)
Operating costs and expenses and amortization of deferred policy acquisition costs	(189)	(180)	(383)	(372)
Restructuring and related charges	(1)	(2)	(1)	(2)
Operating income (loss)	120	139	224	273
Realized capital gains and losses, after-tax	0	38	(32)	110
Valuation changes on embedded derivatives that are not hedged, after-tax	(4)	4	(8)	(1)
DAC and DSI amortization related to realized capital gains and losses and valuation changes on embedded derivatives that are not hedged, after-tax	(1)	(2)	(2)	(2)
Gain (loss) on disposition of operations, after-tax	1	0	2	(1)
Change in accounting for investments in qualified affordable housing projects, after-tax	0	0	0	(17)
Corporate and Other
Operating income (loss)	120	139	224	273
Realized capital gains and losses, after-tax	0	38	(32)	110
Net income applicable to common shareholders	116	179	184	362
Corporate and Other
Segment Reporting Information
Fees and Commissions	1	1	2	2
Property-Liability
Net investment income	11	8	21	16
Income tax (expense) benefit on operations	26	28	51	54
Realized capital gains and losses, after-tax	(1)	0	(1)	0
Allstate Financial
Operating income (loss)	(71)	(75)	(144)	(148)
Realized capital gains and losses, after-tax	(1)	0	(1)	0
Corporate and Other
Operating costs and expenses	(80)	(83)	(160)	(162)
Preferred stock dividends	(29)	(29)	(58)	(58)
Operating income (loss)	(71)	(75)	(144)	(148)
Realized capital gains and losses, after-tax	(1)	0	(1)	0
Net income applicable to common shareholders	$ (72)	$ (75)	$ (145)	(148)
Accounting Standards Update 2014-01 | Property-Liability
Corporate and Other
Income tax expense				$ 28