Acquisition and Disposition - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended			12 Months Ended
	Mar. 15, 2021	Feb. 03, 2021	Jan. 26, 2021	Jan. 04, 2021	Mar. 31, 2021	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2021	Mar. 29, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Goodwill					$ 3,350	$ 3,350				$ 2,369
Long-term debt					7,996	7,996				7,825
Amortization of intangible assets						53	$ 28
Redemption of preferred stock					$ 250
Proceeds from affiliates			$ 2,800
Definitive agreement with Wilton Reassurance									$ 220
Loss on disposition of operations						$ 3,998	$ 0
Noncumulative Preferred Stock | Series A
Business Acquisition [Line Items]
Preferred stock, redemption price par value (in dollars per share)					$ 0.01	$ 0.01
Preferred stock, dividend rate, percentage					7.50%
Noncumulative Preferred Stock | Series B
Business Acquisition [Line Items]
Preferred stock, redemption price par value (in dollars per share)					$ 0.01	0.01
Preferred stock, dividend rate, percentage					7.50%
Non-Cumulative Convertible Preferred Stock | Series D
Business Acquisition [Line Items]
Preferred stock, redemption price par value (in dollars per share)					$ 0.01	$ 0.01
Discontinued Operations, Held-for-sale
Business Acquisition [Line Items]
Amortized cost, net					$ 23,511	$ 23,511				21,417
Equity securities, at fair value, cost					1,191	1,191				1,113
Other short term Investments, amortized cost					1,652	1,652				$ 993
Subordinated Debt
Business Acquisition [Line Items]
Repaid of subordinated notes	$ 72	$ 100
Subsequent acquisition (in percentage)		7.625%
Long-term debt					$ 417	$ 417
Senior Notes
Business Acquisition [Line Items]
Subsequent acquisition (in percentage)					6.75%	6.75%
National General Holdings Corp.
Business Acquisition [Line Items]
Goodwill				$ 980
Purchase accounting fair value adjustment						$ 67
Amortization of intangible assets						23
Amortization expense for the remainder of 2021					$ 228	228
Amortization expense of present value of future profits						134
Fair value purchase accounting adjustments, increase in reserves						74
Fair value purchase accounting adjustments, reduction in investments						13
Fair value purchase accounting adjustments, increase in current and deferred tax liabilities						98
Business acquisition, transaction costs					22	$ 22
National General Holdings Corp. | Forecast
Business Acquisition [Line Items]
Amortization expense of present value of future profits								$ 183
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				$ 616
Present value of future profits					$ 317	$ 317
National General Holdings Corp. | Protection Services
Business Acquisition [Line Items]
Goodwill				29
National General Holdings Corp. | Allstate Health and Benefits
Business Acquisition [Line Items]
Goodwill				$ 335