Related Party Transactions - Agent Loan Sale and Securitization (Details) - Collateralized Loan Obligations - USD ($) $ in Millions	Dec. 31, 2019	Dec. 16, 2019	Dec. 31, 2018	Dec. 22, 2016
Related Party Transactions
Agent loans, fair value		$ 222		$ 419
Affiliate
Related Party Transactions
Agent loans, fair value	$ 641
Class B Deferrable Notes | Class B Deferrable Notes | Affiliate
Related Party Transactions
Agent loans, fair value	214		$ 140
Class C Deferrable Notes | Class B Deferrable Notes | Affiliate
Related Party Transactions
Agent loans, fair value	168		110
Subordinated Notes | Class B Deferrable Notes | Affiliate
Related Party Transactions
Agent loans, fair value	45		29
Notes Due March 9, 2037 | Affiliate
Related Party Transactions
Agent loans, fair value	$ 74
Notes payable interest rate (as a percent)	3.16%
Notes Due March 9, 2037 | Class A Notes | Affiliate
Related Party Transactions
Agent loans, fair value	$ 214
Notes Due March 9, 2037 | Class A Notes | Allstate New Jersey Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	83
Notes Due March 9, 2037 | Class A Notes | American Heritage Life Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	59
Notes Due March 9, 2037 | Class A Notes | Allstate Assurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	33
Notes Due March 9, 2037 | Class A Notes | First Colonial Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	9
Notes Due March 9, 2037 | Class A Notes | Allstate Fire & Casualty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	7
Notes Due March 9, 2037 | Class A Notes | Allstate Property and Casualty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	6
Notes Due March 9, 2037 | Class A Notes | Allstate Indemnity Company | Affiliate
Related Party Transactions
Agent loans, fair value	4
Notes Due March 9, 2037 | Class A Notes | Esurance Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	4
Notes Due March 9, 2037 | Class A Notes | North Light Specialty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	3
Notes Due March 9, 2037 | Class A Notes | Allstate Vehicle and Property Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	2
Notes Due March 9, 2037 | Class A Notes | Allstate New Jersey Property and Casualty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	2
Notes Due March 9, 2037 | Class A Notes | Esurance Property and Casualty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value	2
Notes Due March 10, 2034 | Affiliate
Related Party Transactions
Agent loans, fair value	$ 140		$ 419
Notes payable interest rate (as a percent)	3.36%		3.25%
Notes Due March 10, 2034 | Class A Notes | Affiliate
Related Party Transactions
Agent loans, fair value			$ 140
Notes Due March 10, 2034 | Class A Notes | Allstate New Jersey Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			77
Notes Due March 10, 2034 | Class A Notes | American Heritage Life Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			37
Notes Due March 10, 2034 | Class A Notes | Allstate Assurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			19
Notes Due March 10, 2034 | Class A Notes | First Colonial Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			7
Notes Due March 10, 2034 | Class A Notes | Allstate Fire & Casualty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			0
Notes Due March 10, 2034 | Class A Notes | Allstate Property and Casualty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			0
Notes Due March 10, 2034 | Class A Notes | Allstate Indemnity Company | Affiliate
Related Party Transactions
Agent loans, fair value			0
Notes Due March 10, 2034 | Class A Notes | Esurance Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			0
Notes Due March 10, 2034 | Class A Notes | North Light Specialty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			0
Notes Due March 10, 2034 | Class A Notes | Allstate Vehicle and Property Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			0
Notes Due March 10, 2034 | Class A Notes | Allstate New Jersey Property and Casualty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			0
Notes Due March 10, 2034 | Class A Notes | Esurance Property and Casualty Insurance Company | Affiliate
Related Party Transactions
Agent loans, fair value			$ 0