| **Investments - Fair Values and Unrealized Losses by Investment Category and by Duration of Securities' Continuous Unrealized Loss Position (Details) - USD ($) $ in Millions** | Sep. 30, 2023 | Dec. 31, 2022 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Gross unrealized loss                                                                                                                                                           | $ 1,236       | $ 908         |
| Corporate                                                                                                                                                                       |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Gross unrealized loss                                                                                                                                                           | 700           | 580           |
| States, municipalities and political subdivisions                                                                                                                               |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Gross unrealized loss                                                                                                                                                           | 489           | 303           |
| Government-sponsored enterprises                                                                                                                                                |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Gross unrealized loss                                                                                                                                                           | 23            | 3             |
| United States government                                                                                                                                                        |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Gross unrealized loss                                                                                                                                                           | 6             | 5             |
| Commercial mortgage-backed                                                                                                                                                      |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Gross unrealized loss                                                                                                                                                           | 18            | 16            |
| Foreign government                                                                                                                                                              |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Gross unrealized loss                                                                                                                                                           | 0             | 1             |
| Fixed maturities                                                                                                                                                                |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Less than 12 months Fair Value                                                                                                                                                  | 4,446         | 8,760         |
| Less than 12 Months, Unrealized Loss                                                                                                                                            | 165           | 706           |
| 12 months or more, Fair Value                                                                                                                                                   | 7,757         | 800           |
| 12 months or longer, Unrealized Loss                                                                                                                                            | 1,071         | 202           |
| Total Fair Value                                                                                                                                                                | 12,203        | 9,560         |
| Gross unrealized loss                                                                                                                                                           | 1,236         | 908           |
| Fixed maturities | Corporate                                                                                                                                                    |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Less than 12 months Fair Value                                                                                                                                                  | 1,283         | 5,651         |
| Less than 12 Months, Unrealized Loss                                                                                                                                            | 58            | 412           |
| 12 months or more, Fair Value                                                                                                                                                   | 5,431         | 661           |
| 12 months or longer, Unrealized Loss                                                                                                                                            | 642           | 168           |
| Total Fair Value                                                                                                                                                                | 6,714         | 6,312         |
| Gross unrealized loss                                                                                                                                                           | 700           | 580           |
| Fixed maturities | States, municipalities and political subdivisions                                                                                                            |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Less than 12 months Fair Value                                                                                                                                                  | 2,331         | 2,600         |
| Less than 12 Months, Unrealized Loss                                                                                                                                            | 89            | 274           |
| 12 months or more, Fair Value                                                                                                                                                   | 1,902         | 77            |
| 12 months or longer, Unrealized Loss                                                                                                                                            | 400           | 29            |
| Total Fair Value                                                                                                                                                                | 4,233         | 2,677         |
| Gross unrealized loss                                                                                                                                                           | 489           | 303           |
| Fixed maturities | Government-sponsored enterprises                                                                                                                             |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Less than 12 months Fair Value                                                                                                                                                  | 742           | 123           |
| Less than 12 Months, Unrealized Loss                                                                                                                                            | 17            | 3             |
| 12 months or more, Fair Value                                                                                                                                                   | 95            | 3             |
| 12 months or longer, Unrealized Loss                                                                                                                                            | 6             | 0             |
| Total Fair Value                                                                                                                                                                | 837           | 126           |
| Gross unrealized loss                                                                                                                                                           | 23            | 3             |
| Fixed maturities | United States government                                                                                                                                     |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Less than 12 months Fair Value                                                                                                                                                  | 80            | 146           |
| Less than 12 Months, Unrealized Loss                                                                                                                                            | 1             | 3             |
| 12 months or more, Fair Value                                                                                                                                                   | 130           | 41            |
| 12 months or longer, Unrealized Loss                                                                                                                                            | 5             | 2             |
| Total Fair Value                                                                                                                                                                | 210           | 187           |
| Gross unrealized loss                                                                                                                                                           | 6             | 5             |
| Fixed maturities | Commercial mortgage-backed                                                                                                                                   |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Less than 12 months Fair Value                                                                                                                                                  | 1             | 215           |
| Less than 12 Months, Unrealized Loss                                                                                                                                            | 0             | 13            |
| 12 months or more, Fair Value                                                                                                                                                   | 194           | 14            |
| 12 months or longer, Unrealized Loss                                                                                                                                            | 18            | 3             |
| Total Fair Value                                                                                                                                                                | 195           | 229           |
| Gross unrealized loss                                                                                                                                                           | 18            | 16            |
| Fixed maturities | Foreign government                                                                                                                                           |          |          |
| **Investments, Unrealized Loss Position**                                                                                                                                       |          |          |
| Less than 12 months Fair Value                                                                                                                                                  | 9             | 25            |
| Less than 12 Months, Unrealized Loss                                                                                                                                            | 0             | 1             |
| 12 months or more, Fair Value                                                                                                                                                   | 5             | 4             |
| 12 months or longer, Unrealized Loss                                                                                                                                            | 0             | 0             |
| Total Fair Value                                                                                                                                                                | 14            | 29            |
| Gross unrealized loss                                                                                                                                                           | $ 0           | $ 1           |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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| - Definition
Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
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| - Definition
Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
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| - Definition
Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
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