Reporting Segments (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Property-Liability
Net investment income	$ 850us-gaap_NetInvestmentIncome	$ 959us-gaap_NetInvestmentIncome
Allstate Financial
Life and annuity premiums and contract charges	537	607
Restructuring and related charges	(4)us-gaap_RestructuringCharges	(6)us-gaap_RestructuringCharges
Corporate and Other
Net income available to common shareholders	648	587
Property-Liability
Property-Liability
Underwriting income	467	372
Net investment income	358	312
Realized capital gains and losses, after-tax	18	34
Allstate Financial
Realized capital gains and losses, after-tax	18	34
Income tax (expense) benefit on operations	(305)	(225)
Corporate and Other
Realized capital gains and losses, after-tax	18	34
Net income available to common shareholders	538	493
Allstate Protection
Property-Liability
Underwriting income	469	375
Discontinued Lines and Coverages
Property-Liability
Underwriting income	(2)	(3)
Allstate Financial
Property-Liability
Net investment income	484	640
Realized capital gains and losses, after-tax	72	0
Allstate Financial
Life and annuity premiums and contract charges	537	607
Contract benefits and interest credited to contractholder funds	(633)	(779)
Operating costs and expenses and amortization of deferred policy acquisition costs	(192)	(192)
Restructuring and related charges	0	(2)
Operating income (loss)	134	189
Realized capital gains and losses, after-tax	72	0
Valuation changes on embedded derivatives that are not hedged, after-tax	(5)	(11)
Loss on disposition of operations, after-tax	(1)	(16)
Change in accounting for investments in qualified affordable housing projects, after-tax	(17)	0
Income tax (expense) benefit on operations	(62)	(85)
Corporate and Other
Operating income (loss)	134	189
Realized capital gains and losses, after-tax	72	0
Net income available to common shareholders	183	162
Corporate and Other
Segment Reporting Information
Fees and Commissions	1	2
Property-Liability
Net investment income	8	7
Realized capital gains and losses, after-tax	0	1
Allstate Financial
Operating income (loss)	(73)	(69)
Realized capital gains and losses, after-tax	0	1
Income tax (expense) benefit on operations	26	32
Corporate and Other
Operating income (loss)	(73)	(69)
Operating costs and expenses	(79)	(97)
Preferred stock dividends	(29)	(13)
Realized capital gains and losses, after-tax	0	1
Net income available to common shareholders	$ (73)	$ (68)

Contract benefits and interest credited to contract holder funds.

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The amount of operating costs and expenses and amortization of deferred policy acquisition costs.

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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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The income tax expense (benefit) pertaining to operating income or loss as measured by the entity for segment reporting purposes.

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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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The net realized gains or losses on investments during the period after tax effect.

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The operating cost and expenses 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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No definition available.

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The amount of valuation changes on embedded derivatives that are not hedged, net of tax effect.

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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-Topic 505

-SubTopic 10

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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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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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-Article 12

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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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-Subsection 3, 4

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