| **Investments - Analysis of Cost or Amortized Cost, Gross Unrealized Gains and Losses and Fair Value for Investments (Details) - USD ($) $ in Millions** | Sep. 30, 2024 | Dec. 31, 2023 |
|----------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Debt Securities, Available-for-sale**                                                                                                                  |          |          |
| Total                                                                                                                                                    | $ 16,074      | $ 14,361      |
| Gross unrealized gain                                                                                                                                    | 201           | 117           |
| Gross unrealized loss                                                                                                                                    | 404           | 687           |
| Fixed maturities, at fair value                                                                                                                          | 15,871        | 13,791        |
| Corporate                                                                                                                                                |          |          |
| **Debt Securities, Available-for-sale**                                                                                                                  |          |          |
| Total                                                                                                                                                    | 8,407         | 7,836         |
| Gross unrealized gain                                                                                                                                    | 150           | 70            |
| Gross unrealized loss                                                                                                                                    | 218           | 454           |
| Fixed maturities, at fair value                                                                                                                          | 8,339         | 7,452         |
| States, municipalities and political subdivisions                                                                                                        |          |          |
| **Debt Securities, Available-for-sale**                                                                                                                  |          |          |
| Total                                                                                                                                                    | 4,944         | 4,867         |
| Gross unrealized gain                                                                                                                                    | 41            | 44            |
| Gross unrealized loss                                                                                                                                    | 176           | 208           |
| Fixed maturities, at fair value                                                                                                                          | 4,809         | 4,703         |
| Government-sponsored enterprises                                                                                                                         |          |          |
| **Debt Securities, Available-for-sale**                                                                                                                  |          |          |
| Total                                                                                                                                                    | 2,147         | 1,227         |
| Gross unrealized gain                                                                                                                                    | 5             | 3             |
| Gross unrealized loss                                                                                                                                    | 1             | 6             |
| Fixed maturities, at fair value                                                                                                                          | 2,151         | 1,224         |
| Asset-backed                                                                                                                                             |          |          |
| **Debt Securities, Available-for-sale**                                                                                                                  |          |          |
| Total                                                                                                                                                    | 317           | 203           |
| Gross unrealized gain                                                                                                                                    | 4             | 0             |
| Gross unrealized loss                                                                                                                                    | 7             | 16            |
| Fixed maturities, at fair value                                                                                                                          | 314           | 187           |
| United States government                                                                                                                                 |          |          |
| **Debt Securities, Available-for-sale**                                                                                                                  |          |          |
| Total                                                                                                                                                    | 228           | 203           |
| Gross unrealized gain                                                                                                                                    | 1             | 0             |
| Gross unrealized loss                                                                                                                                    | 2             | 3             |
| Fixed maturities, at fair value                                                                                                                          | 227           | 200           |
| Foreign government                                                                                                                                       |          |          |
| **Debt Securities, Available-for-sale**                                                                                                                  |          |          |
| Total                                                                                                                                                    | 31            | 25            |
| Gross unrealized gain                                                                                                                                    | 0             | 0             |
| Gross unrealized loss                                                                                                                                    | 0             | 0             |
| Fixed maturities, at fair value                                                                                                                          | $ 31          | $ 25          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, before tax, of unrealized gain 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, 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).
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| - Definition
Amortized cost, after allowance for credit loss, of 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
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
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