Reporting Segments (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Property-Liability
Net investment income	$ 897	$ 762	$ 1,645	$ 1,493
Restructuring and related charges	(53)	(11)	(63)	(16)
Allstate Financial
Life and annuity premiums and contract charges	591	564	1,184	1,130
Corporate and Other
Net income applicable to common shareholders	550	242	1,216	459
Allstate Protection
Property-Liability
Underwriting income (loss)	232	(64)	741	63
Discontinued Lines and Coverages
Property-Liability
Underwriting income (loss)	(5)	(2)	(7)	(4)
Property-Liability
Property-Liability
Underwriting income (loss)	227	(66)	734	59
Net investment income	391	316	702	618
Income tax (expense) benefit on operations	(196)	(70)	(451)	(211)
Realized capital gains and losses, after-tax	56	18	145	(46)
Allstate Financial
Realized capital gains and losses, after-tax	56	18	145	(46)
Gain on disposition of operations, after-tax	6	0	6	0
Corporate and Other
Realized capital gains and losses, after-tax	56	18	145	(46)
Net income applicable to common shareholders	484	198	1,136	420
Allstate Financial
Property-Liability
Net investment income	496	435	922	854
Restructuring and related charges	(1)	(1)	(1)	(1)
Income tax (expense) benefit on operations	(75)	(56)	(127)	(104)
Realized capital gains and losses, after-tax	(3)	0	(4)	(32)
Allstate Financial
Life and annuity premiums and contract charges	591	564	1,184	1,130
Contract benefits and interest credited to contractholder funds	(659)	(633)	(1,306)	(1,272)
Operating costs and expenses and amortization of deferred policy acquisition costs	(199)	(189)	(409)	(383)
Operating income (loss)	153	120	263	224
Realized capital gains and losses, after-tax	(3)	0	(4)	(32)
Valuation changes on embedded derivatives that are not hedged, after-tax	(1)	(4)	(1)	(8)
DAC and DSI amortization related to realized capital gains and losses and valuation changes on embedded derivatives that are not hedged, after-tax	(3)	(1)	(6)	(2)
Gain on disposition of operations, after-tax	0	1	2	2
Corporate and Other
Operating income (loss)	153	120	263	224
Realized capital gains and losses, after-tax	(3)	0	(4)	(32)
Net income applicable to common shareholders	146	116	254	184
Corporate and Other
Property-Liability
Net investment income	10	11	21	21
Income tax (expense) benefit on operations	31	26	61	51
Realized capital gains and losses, after-tax	0	(1)	0	(1)
Allstate Financial
Operating income (loss)	(80)	(71)	(161)	(144)
Realized capital gains and losses, after-tax	0	(1)	0	(1)
Corporate and Other
Operating costs and expenses	(92)	(79)	(185)	(158)
Preferred stock dividends	(29)	(29)	(58)	(58)
Operating income (loss)	(80)	(71)	(161)	(144)
Realized capital gains and losses, after-tax	0	(1)	0	(1)
Business combination expenses, after-tax	0	0	(13)	0
Net income applicable to common shareholders	$ (80)	$ (72)	$ (174)	$ (145)