Acquisitions and Dispositions - Narrative (Details) $ / shares in Units, $ in Millions							1 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended
	Nov. 01, 2021 USD ($)	Oct. 01, 2021 USD ($)	Jul. 15, 2021 USD ($) $ / shares	Mar. 15, 2021 USD ($)	Feb. 03, 2021 USD ($)	Jan. 04, 2021 USD ($)	Nov. 01, 2021 USD ($)	Sep. 30, 2021 USD ($) state $ / shares	Mar. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) state $ / shares	Sep. 30, 2020 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) $ / shares
Business Acquisition [Line Items]
Goodwill								$ 3,389				$ 3,389			$ 2,369
Long-term debt								7,980				7,980			$ 7,825
Amortization of purchased intangibles								$ 109			$ 31	$ 267	$ 88
Preferred stock, par value (in dollars per share) | $ / shares								$ 1				$ 1			$ 1
Redemption of preferred stock										$ 250
Loss on disposition of operations, net of tax									$ 4,000			$ 3,754	$ 0
Subsequent Event
Business Acquisition [Line Items]
Definitive agreement with Wilton Reassurance	$ 2,800	$ 400					$ 2,800
Proceeds from affiliates	$ 4,000
Loss on disposition of operations, net of tax							$ 3,800
Noncumulative Preferred Stock
Business Acquisition [Line Items]
Redemption of preferred stock			$ 200
Noncumulative Preferred Stock | Series A
Business Acquisition [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares								0.01				$ 0.01
Preferred stock, dividend rate, percentage										7.50%
Noncumulative Preferred Stock | Series B
Business Acquisition [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares								0.01				0.01
Preferred stock, dividend rate, percentage										7.50%
Noncumulative Preferred Stock | Series C
Business Acquisition [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.01
Preferred stock, dividend rate, percentage			7.50%
Non-Cumulative Convertible Preferred Stock | Series D
Business Acquisition [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares								$ 0.01				$ 0.01
Depository Shares
Business Acquisition [Line Items]
Depository shares, as a ratio of preferred stock								0.025				0.025
Discontinued Operations, Held-for-sale
Business Acquisition [Line Items]
Amortized cost, net								$ 25,673				$ 25,673			$ 21,417
Equity securities, at fair value, cost								23				23			1,113
Other short term Investments, amortized cost								1,155				1,155			$ 993
Subordinated Debt
Business Acquisition [Line Items]
Repaid of subordinated notes				$ 72	$ 100
Subsequent acquisition (in percentage)					7.625%
Long-term debt								$ 350				$ 350
Senior Notes
Business Acquisition [Line Items]
Subsequent acquisition (in percentage)								6.75%				6.75%
SafeAuto
Business Acquisition [Line Items]
Number of states acquiree operates in | state								28				28
SafeAuto | Subsequent Event
Business Acquisition [Line Items]
Cash to acquire businesses		$ 262
National General Holdings Corp.
Business Acquisition [Line Items]
Goodwill						$ 1,010
Purchase accounting fair value adjustment												$ 50
Amortization of purchased intangibles								$ 76				175
Amortization expense for the remainder of 2021								76				76
Amortization expense of present value of future profits								$ 61				293
Fair value purchase accounting adjustments, increase in reserves												62
Fair value purchase accounting adjustments, reduction in investments												13
Fair value purchase accounting adjustments, increase in current and deferred tax liabilities												128
Transaction costs												$ 22
National General Holdings Corp. | Noncumulative Preferred Stock | Series C
Business Acquisition [Line Items]
Preferred stock, dividend rate, percentage			7.50%
National General Holdings Corp. | Depository Shares
Business Acquisition [Line Items]
Depository shares, as a ratio of preferred stock			0.025
National General Holdings Corp. | Forecast
Business Acquisition [Line Items]
Amortization expense of present value of future profits														$ 24
National General Holdings Corp. | Minimum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)						3 years						6 months
National General Holdings Corp. | Maximum
Business Acquisition [Line Items]
Finite-lived intangible asset, useful life (in years)						10 years						12 months
National General Holdings Corp. | Allstate Protection
Business Acquisition [Line Items]
Goodwill						$ 637
Present value of future profits						317
National General Holdings Corp. | Protection Services
Business Acquisition [Line Items]
Goodwill						22
National General Holdings Corp. | Allstate Health and Benefits
Business Acquisition [Line Items]
Goodwill						$ 351