Acquisitions and Disposition - Narrative (Details) $ / shares in Units, $ in Millions									12 Months Ended
	Dec. 17, 2021 USD ($)	Nov. 01, 2021 USD ($)	Oct. 01, 2021 USD ($)	Jul. 15, 2021 USD ($) $ / shares	Mar. 15, 2021 USD ($)	Feb. 03, 2021 USD ($)	Feb. 02, 2021 USD ($) $ / shares	Jan. 04, 2021 USD ($)	Dec. 31, 2021 USD ($) state $ / shares	Dec. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Goodwill									$ 3,502	$ 2,369
Long-term debt									7,976	7,825
Amortization of intangible assets									376	118	$ 126
Present value of future profits									$ 24	$ 23
Preferred stock, par or stated value per share (in USD per share) | $ / shares									$ 1	$ 1
Redemption of preferred stock							$ 250
Loss on disposition of operations, net of tax									$ 4,031	$ 0	$ 0
Allstate Life Insurance Company Of New York | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Business Acquisition [Line Items]
Definitive agreement with Wilton Reassurance			$ 400
Allstate Life Insurance Company | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Business Acquisition [Line Items]
Proceeds from affiliates		$ 4,000
Pre-close dividend received		$ 1,250
ALNY And ALIC | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Business Acquisition [Line Items]
Loss on disposition of operations, net of tax									$ 4,090
Customers relationships
Business Acquisition [Line Items]
Finite-Lived intangible asset, useful life									10 years
Noncumulative Perpetual Preferred Stock
Business Acquisition [Line Items]
Preferred stock, par or stated value per share (in USD per share) | $ / shares									$ 1.00
Redemption of preferred stock				$ 200
Depository Shares
Business Acquisition [Line Items]
Depository shares, as a ratio of preferred stock									0.025
Series A | Noncumulative Perpetual Preferred Stock
Business Acquisition [Line Items]
Dividend rate							7.50%
Preferred stock, par or stated value per share (in USD per share) | $ / shares							$ 0.01
Series B | Noncumulative Perpetual Preferred Stock
Business Acquisition [Line Items]
Dividend rate							7.50%
Preferred stock, par or stated value per share (in USD per share) | $ / shares							$ 0.01
Series D | Non-Cumulative Convertible Preferred Stock
Business Acquisition [Line Items]
Preferred stock, par or stated value per share (in USD per share) | $ / shares							$ 0.01
Series C | Noncumulative Perpetual Preferred Stock
Business Acquisition [Line Items]
Dividend rate				7.50%
Preferred stock, par or stated value per share (in USD per share) | $ / shares				$ 0.01
Allstate Protection
Business Acquisition [Line Items]
Goodwill									$ 1,563	810
Number of states in which entity operates | state									50
Protection Services
Business Acquisition [Line Items]
Goodwill									$ 1,494	$ 1,463
Allstate Health and Benefits
Business Acquisition [Line Items]
Number of states in which entity operates | state									50
Subordinated Debentures
Business Acquisition [Line Items]
Repayments of debt					$ 72	$ 100
Note stated interest rate (as a percent)						7.625%
Senior Notes
Business Acquisition [Line Items]
Note stated interest rate (as a percent)									6.75%
Long-term debt									$ 350
National General Holdings Corp.
Business Acquisition [Line Items]
Goodwill								$ 1,038
Purchase accounting fair value adjustment									45
Amortization of intangible assets									251
Fair value purchase accounting adjustments, increase in reserves									62
Fair value purchase accounting adjustments, reduction in investments									9
Fair value purchase accounting adjustments, increase in current and deferred tax liabilities									153
Transaction costs									$ 22
Intangible assets								1,199
National General Holdings Corp. | Licenses
Business Acquisition [Line Items]
Intangible assets								$ 97
National General Holdings Corp. | Depository Shares
Business Acquisition [Line Items]
Depository shares, as a ratio of preferred stock				0.025
National General Holdings Corp. | Series C | Noncumulative Perpetual Preferred Stock
Business Acquisition [Line Items]
Dividend rate				7.50%
National General Holdings Corp. | Minimum
Business Acquisition [Line Items]
Finite-Lived intangible asset, useful life								3 years	6 months
National General Holdings Corp. | Maximum
Business Acquisition [Line Items]
Finite-Lived intangible asset, useful life								10 years	12 months
National General Holdings Corp. | Allstate Protection
Business Acquisition [Line Items]
Goodwill								$ 675
Present value of future profits								317
National General Holdings Corp. | Protection Services
Business Acquisition [Line Items]
Goodwill								20
National General Holdings Corp. | Allstate Health and Benefits
Business Acquisition [Line Items]
Goodwill								$ 343
SafeAuto
Business Acquisition [Line Items]
Goodwill			79
Redemption of preferred stock	$ 13
Number of states in which entity operates | state									28
Payments to acquire businesses			262
Intangible assets			30
Value of business acquired			7
SafeAuto | Customers relationships
Business Acquisition [Line Items]
Intangible assets			24
SafeAuto | Licenses
Business Acquisition [Line Items]
Intangible assets			$ 6