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Related Party Transactions - Narrative and Other (Details) - USD ($)			12 Months Ended
	Jan. 01, 2017	Dec. 02, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 16, 2019	Dec. 31, 2016	Dec. 22, 2016
Related Party Transactions
Allocation of operating expenses			$ 211,000,000	$ 235,000,000	$ 243,000,000
Cash			43,000,000	52,000,000	145,000,000		$ 138,000,000
Notes due to related parties			214,000,000	140,000,000
Interest expense			5,000,000		5,000,000
Reserves recorded for annuities			11,272,000,000	11,239,000,000
Surplus note			4,406,000,000	5,444,000,000	4,698,000,000
Liquidity agreement
Related Party Transactions
Amount of loan outstanding under agreement			0	0
Liquidity agreement \| Maximum
Related Party Transactions
Amount available for borrowings under the agreement			$ 1,000,000,000
Advances Maturity Period			364 days
Liquidity agreement \| Minimum
Related Party Transactions
Notice period for payables on demand			10 days
Intercompany loan agreement
Related Party Transactions
Amount of loan outstanding under agreement			$ 0	0
Intercompany loan agreement \| Maximum
Related Party Transactions
Amount available for borrowings under the agreement			1,000,000,000
Revolving loan credit agreement
Related Party Transactions
Amount of loan outstanding under agreement			0	0
Capital support agreement
Related Party Transactions
Amount of loan outstanding under agreement			$ 0	0
Commitment fee as a percentage of the amount of the capital and surplus maximum that remains available at the beginning of the period			1.00%
Capital support agreement \| Maximum
Related Party Transactions
Amount available for borrowings under the agreement			$ 1,000,000,000
Capital support agreement \| Minimum
Related Party Transactions
Percentage of risk-based capital ratio			150.00%
Minimum risk-based capital ratio at which agreement will be terminated (as a percent)			300.00%
Voting stock to be held as per agreement (as a percent)			50.00%
Structured settlement annuities \| AIC
Related Party Transactions
Reserves recorded for annuities			$ 4,570,000,000	4,590,000,000
Affiliate
Related Party Transactions
Fee and Commission Expenses			3,000,000	3,000,000	9,000,000
Allstate Financial Services, LLC
Related Party Transactions
Payments of dividends			75,000,000	250,000,000	600,000,000
Allstate Finance Company Agency Loans LLC \| Beneficial Owner
Related Party Transactions
Agent loans			612,000,000	407,000,000
Cash			1,000,000	2,000,000
Notes due to related parties			214,000,000	140,000,000
AAC \| Subsidiary of Common Parent
Related Party Transactions
Notes payable interest rate (as a percent)		3.07%
Interest income, related party			1,000,000	1,000,000	1,000,000
Surplus note		$ 40,000,000
AAC \| Affiliate
Related Party Transactions
Proceeds from coinsurance reinsurance agreement	$ 20,000,000
DAC, additions	45,000,000
Additions to other assets, amount	11,000,000
Reinsurance, reserve for life-contingent contract benefits	24,000,000
Deferred tax liabilities	18,000,000
Collateralized Loan Obligations
Related Party Transactions
Agent loans, fair value						$ 222,000,000		$ 419,000,000
Collateralized Loan Obligations \| Affiliate
Related Party Transactions
Agent loans, fair value			641,000,000
Additional capital paid-in
Related Party Transactions
Gain (Loss) on the transaction			0	$ 0	$ (34,000,000)
Additional capital paid-in \| AAC \| Affiliate
Related Party Transactions
Gain (Loss) on the transaction	$ (34,000,000)
Hybrid Instrument \| Subsidiary of Common Parent \| ALIC Reinsurance Company
Related Party Transactions
Credit derivative, maximum exposure, undiscounted			$ 1,750,000,000