Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Non-cash modifications of certain mortgage loans, fixed income securities, limited partnerships and other investments, as well as mergers completed with equity securities	$ 51	$ 117	$ 96
Liabilities assumed		34
Redemption, related party debt	0	140	0
Notes due to related parties	140	465
Liabilities for collateral received reported in other liabilities and accrued expenses	539	545	539
Obligations to return cash collateral for over-the-counter ("OTC") derivatives reported in other liabilities and accrued expenses or other investments	3	5	11
Net change in proceeds managed
Net change in fixed income securities	149	(277)	0
Net change in short-term investments	(142)	277	(41)
Operating cash flow provided (used)	7	0	(41)
Net change in cash	1	0	1
Net change in proceeds managed	8	0	(40)
Net change in liabilities
Liabilities for collateral, beginning of year	(550)	(550)	(510)
Liabilities for collateral, end of year	(542)	(550)	(550)
Operating cash flow (used) provided	(8)	0	40
Other
Debt Instrument [Line Items]
Decrease in notes receivable, related parties	325
Debt and Equity Securities
Debt Instrument [Line Items]
Payments of dividends			86
Allstate Financial Services, LLC
Debt Instrument [Line Items]
Payments of dividends	600		103
ALIC Re \| Affiliate
Debt Instrument [Line Items]
Redemption, related party debt	325
4.14% Surplus Note, due 2036 \| ALIC Re \| Kennett
Debt Instrument [Line Items]
Notes due to related parties		50
Limited Partnership
Debt Instrument [Line Items]
Liabilities assumed	$ 34	$ 56	$ 44

The net operating cash flow provided by (used in) the net change in liabilities for collateral.

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The net operating cash flow provided or used related to collateral received in conjunction with the entity's securities lending and over-the-counter derivatives.

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The net change in cash from the proceeds managed related to collateral received in conjunction with the entity's securities lending and over-the-counter derivatives.

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The net change in the proceeds managed related to collateral received in conjunction with the entity's securities lending and over-the-counter derivatives.

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The net change in short-term investments from the proceeds managed related to collateral received in conjunction with the entity's securities lending and over-the-counter derivatives.

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Net Change in Fixed Income Term Investments of Proceeds Managed Collateral

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The liability to return cash and securities received as collateral in conjunction with securities lending and over-the-counter derivatives.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The increase (decrease) during the reporting period in the amount owed to the reporting entity in the form of loans and obligations (generally evidenced by promissory notes) made to the following types of related parties: a parent company and its subsidiaries; subsidiaries of a common parent; an entity and trust for the benefit of employees, such as pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management, an entity and its principal owners, management, or member of their immediate families, affiliates, or other parties with the ability to exert significant influence.

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The fair value of liabilities assumed in noncash investing or financing activities.

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The amount for notes payable (written promise to pay), due to related parties.

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The fair value of collateral received by the entity associated with securities borrowed that must be returned if the counterparty fulfills its obligations. It appears on the balance sheet as a liability and has a corresponding asset that appears on the balance sheet called Securities Received as Collateral.

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Cash outflow in the form of capital distributions and dividends to common shareholders, preferred shareholders and noncontrolling interests.

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Value of investments transferred from the entity's investments in noncash transactions.

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