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Acquisitions and Dispositions - Narrative (Details) $ / shares in Units, $ in Millions |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
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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 |  |  |  |  |  |  |  |  |

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