Reporting Segments (Details 2) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Property-Liability
Net investment income	$ 748	$ 731
Allstate Financial
Life and annuity premiums and contract charges	593	566
Corporate and Other
Net income applicable to common shareholders	666	217
Allstate Protection
Property-Liability
Underwriting income	509	127
Discontinued Lines and Coverages
Property-Liability
Underwriting income	(2)	(2)
Property-Liability
Property-Liability
Underwriting income	507	125
Net investment income	311	302
Income tax (expense) benefit on operations	(255)	(141)
Realized capital gains and losses, after-tax	89	(64)
Allstate Financial
Realized capital gains and losses, after-tax	89	(64)
Corporate and Other
Realized capital gains and losses, after-tax	89	(64)
Net income applicable to common shareholders	652	222
Allstate Financial
Property-Liability
Net investment income	426	419
Income tax (expense) benefit on operations	(52)	(48)
Realized capital gains and losses, after-tax	(1)	(32)
Allstate Financial
Life and annuity premiums and contract charges	593	566
Contract benefits and interest credited to contractholder funds	(647)	(639)
Operating costs and expenses and amortization of deferred policy acquisition costs	(210)	(194)
Operating income (loss)	110	104
Realized capital gains and losses, after-tax	(1)	(32)
Valuation changes on embedded derivatives that are not hedged, after-tax	0	(4)
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)
Gain on disposition of operations, after-tax	2	1
Corporate and Other
Operating income (loss)	110	104
Realized capital gains and losses, after-tax	(1)	(32)
Net income applicable to common shareholders	108	68
Corporate and Other
Property-Liability
Net investment income	11	10
Income tax (expense) benefit on operations	30	25
Realized capital gains and losses, after-tax	0	0
Allstate Financial
Operating income (loss)	(81)	(73)
Realized capital gains and losses, after-tax	0	0
Corporate and Other
Service fees	1	1
Operating costs and expenses	(94)	(80)
Preferred stock dividends	(29)	(29)
Operating income (loss)	(81)	(73)
Realized capital gains and losses, after-tax	0	0
Business combination expenses, after-tax	(13)	0
Net income applicable to common shareholders	$ (94)	$ (73)