| **Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions** | Sep. 30, 2022 | Dec. 31, 2021 |
|----------------------------------------------------------------------------------------------------|---------------|---------------|
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | $ 28,394      | $ 5,695       |
| Gross Unrealized Losses, Less than 12 Months                                                       | 4,152         | 92            |
| Estimated Fair Value, 12 Months or Longer                                                          | 1,550         | 370           |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 431           | 20            |
| Estimated Fair Value, Total                                                                        | 29,944        | 6,065         |
| Gross Unrealized Losses, Total                                                                     | 4,583         | 112           |
| Corporate and other bonds                                                                          |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 16,707        | 2,389         |
| Gross Unrealized Losses, Less than 12 Months                                                       | 2,117         | 48            |
| Estimated Fair Value, 12 Months or Longer                                                          | 914           | 136           |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 281           | 8             |
| Estimated Fair Value, Total                                                                        | 17,621        | 2,525         |
| Gross Unrealized Losses, Total                                                                     | 2,398         | 56            |
| States, municipalities and political subdivisions                                                  |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 4,793         | 730           |
| Gross Unrealized Losses, Less than 12 Months                                                       | 1,029         | 14            |
| Estimated Fair Value, 12 Months or Longer                                                          | 128           | 0             |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 51            | 0             |
| Estimated Fair Value, Total                                                                        | 4,921         | 730           |
| Gross Unrealized Losses, Total                                                                     | 1,080         | 14            |
| Asset-backed                                                                                       |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 6,387         | 2,410         |
| Gross Unrealized Losses, Less than 12 Months                                                       | 963           | 25            |
| Estimated Fair Value, 12 Months or Longer                                                          | 483           | 229           |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 93            | 12            |
| Estimated Fair Value, Total                                                                        | 6,870         | 2,639         |
| Gross Unrealized Losses, Total                                                                     | 1,056         | 37            |
| Residential mortgage-backed                                                                        |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 2,582         | 1,043         |
| Gross Unrealized Losses, Less than 12 Months                                                       | 462           | 8             |
| Estimated Fair Value, 12 Months or Longer                                                          | 17            | 0             |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 8             | 0             |
| Estimated Fair Value, Total                                                                        | 2,599         | 1,043         |
| Gross Unrealized Losses, Total                                                                     | 470           | 8             |
| Commercial mortgage-backed                                                                         |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 1,372         | 527           |
| Gross Unrealized Losses, Less than 12 Months                                                       | 194           | 7             |
| Estimated Fair Value, 12 Months or Longer                                                          | 233           | 167           |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 43            | 12            |
| Estimated Fair Value, Total                                                                        | 1,605         | 694           |
| Gross Unrealized Losses, Total                                                                     | 237           | 19            |
| Other asset-backed                                                                                 |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 2,433         | 840           |
| Gross Unrealized Losses, Less than 12 Months                                                       | 307           | 10            |
| Estimated Fair Value, 12 Months or Longer                                                          | 233           | 62            |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 42            | 0             |
| Estimated Fair Value, Total                                                                        | 2,666         | 902           |
| Gross Unrealized Losses, Total                                                                     | 349           | 10            |
| U.S. Treasury and obligations of government-sponsored enterprises                                  |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 61            | 69            |
| Gross Unrealized Losses, Less than 12 Months                                                       | 1             | 3             |
| Estimated Fair Value, 12 Months or Longer                                                          | 0             | 5             |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 0             | 0             |
| Estimated Fair Value, Total                                                                        | 61            | 74            |
| Gross Unrealized Losses, Total                                                                     | 1             | 3             |
| Foreign government                                                                                 |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 446           | 97            |
| Gross Unrealized Losses, Less than 12 Months                                                       | 42            | 2             |
| Estimated Fair Value, 12 Months or Longer                                                          | 25            | 0             |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 6             | 0             |
| Estimated Fair Value, Total                                                                        | 471           | 97            |
| Gross Unrealized Losses, Total                                                                     | $ 48          | $ 2           |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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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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 unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.
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