Reporting Segments (Details 2) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Property-Liability
Net investment income	$ 748	$ 807	$ 2,241	$ 2,446
Allstate Financial
Life and annuity premiums and contract charges	571	538	1,701	1,611
Restructuring and related charges	(5)	(9)	(21)	(32)
Corporate and Other
Net income applicable to common shareholders	491	621	950	1,595
Income tax expense	245	305	459	880
Allstate Protection
Property-Liability
Underwriting income	455	540	518	1,001
Discontinued Lines and Coverages
Property-Liability
Underwriting income	(100)	(49)	(104)	(53)
Property-Liability
Property-Liability
Underwriting income	355	491	414	948
Net investment income	310	307	928	957
Income tax (expense) benefit on operations	(218)	(256)	(429)	(653)
Realized capital gains and losses, after-tax	36	(104)	(10)	(55)
Allstate Financial
Realized capital gains and losses, after-tax	36	(104)	(10)	(55)
Gain on disposition of operations, after-tax	0	(1)	0	0
Corporate and Other
Realized capital gains and losses, after-tax	36	(104)	(10)	(55)
Net income applicable to common shareholders	483	437	903	1,197
Allstate Financial
Property-Liability
Net investment income	427	491	1,281	1,464
Income tax (expense) benefit on operations	(43)	(66)	(147)	(195)
Realized capital gains and losses, after-tax	(14)	125	(46)	235
Allstate Financial
Life and annuity premiums and contract charges	571	538	1,701	1,611
Contract benefits and interest credited to contractholder funds	(667)	(651)	(1,939)	(1,921)
Operating costs and expenses and amortization of deferred policy acquisition costs	(194)	(173)	(577)	(545)
Restructuring and related charges	0	(1)	(1)	(3)
Operating income (loss)	94	138	318	411
Realized capital gains and losses, after-tax	(14)	125	(46)	235
Valuation changes on embedded derivatives that are not hedged, after-tax	0	(2)	(8)	(3)
DAC and DSI amortization related to realized capital gains and losses and valuation changes on embedded derivatives that are not hedged, after-tax	(1)	(1)	(3)	(3)
Gain on disposition of operations, after-tax	1	2	3	1
Change in accounting for investments in qualified affordable housing projects, after-tax	0	0	0	(17)
Corporate and Other
Operating income (loss)	94	138	318	411
Realized capital gains and losses, after-tax	(14)	125	(46)	235
Net income applicable to common shareholders	80	262	264	624
Corporate and Other
Property-Liability
Net investment income	11	9	32	25
Income tax (expense) benefit on operations	26	28	77	82
Realized capital gains and losses, after-tax	0	0	(1)	0
Allstate Financial
Operating income (loss)	(72)	(78)	(216)	(226)
Realized capital gains and losses, after-tax	0	0	(1)	0
Corporate and Other
Service fees	1	0	3	2
Operating costs and expenses	(81)	(86)	(241)	(248)
Preferred stock dividends	(29)	(29)	(87)	(87)
Operating income (loss)	(72)	(78)	(216)	(226)
Realized capital gains and losses, after-tax	0	0	(1)	0
Net income applicable to common shareholders	$ (72)	$ (78)	$ (217)	(226)
Accounting Standards Update 2014-01 \| Property-Liability
Corporate and Other
Income tax expense				$ 28

Contract benefits and interest credited to contract holder funds.

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The amount of deferred policy acquisition costs and sales inducement costs (amortization) accretion related to realized capital gains and losses and valuation changes on embedded derivatives that are not hedged, net of tax effect.

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The gain (loss) resulting from the sale of a disposal group that is not a discontinued operation, net of tax effect.

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Premiums recognized as revenue in the period on all life insurance and reinsurance contracts, as well as accident and health insurance and reinsurance contracts, after subtracting any amounts ceded to another insurer. Also includes an amount that an insurer adds to a policy's premium, or deducts from a policy's cash value or contract holder's account, as compensation for services rendered (may include fees), after subtracting any amounts ceded to another insurer.

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The operating income (loss), net of tax effect, as measured by the entity for segment reporting purposes.

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A measure that is not based on GAAP, which is calculated as premiums earned, less claims and claims expense ("losses"), amortization of deferred policy acquisition costs ("DAC"), operating costs and expenses and restructuring and related charges, as determined using GAAP.

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Amount of paid and unpaid preferred stock dividends declared with the form of settlement in cash.

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Amount of fees and commissions from financial services and banking activities and correspondent clearing. Includes fees from depositor accounts, credit cards, merchant discounts, and fiduciary and trust activities, guarantee fees, investment advisory, management, and administrative fees, transfer agent fees, and insurance commissions.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount of the effect of a change in accounting principle on net income.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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