| **Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions** | Sep. 30, 2023 | Dec. 31, 2022 |
|----------------------------------------------------------------------------------------------------|---------------|---------------|
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | $ 9,836       | $ 25,234      |
| Gross Unrealized Losses, Less than 12 Months                                                       | 605           | 2,946         |
| Estimated Fair Value, 12 Months or Longer                                                          | 21,281        | 4,277         |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 4,283         | 1,110         |
| Estimated Fair Value, Total                                                                        | 31,117        | 29,511        |
| Gross Unrealized Losses, Total                                                                     | 4,888         | 4,056         |
| Corporate and other bonds                                                                          |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 6,374         | 15,946        |
| Gross Unrealized Losses, Less than 12 Months                                                       | 378           | 1,585         |
| Estimated Fair Value, 12 Months or Longer                                                          | 12,794        | 1,634         |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 2,059         | 424           |
| Estimated Fair Value, Total                                                                        | 19,168        | 17,580        |
| Gross Unrealized Losses, Total                                                                     | 2,437         | 2,009         |
| States, municipalities and political subdivisions                                                  |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 1,593         | 4,079         |
| Gross Unrealized Losses, Less than 12 Months                                                       | 138           | 769           |
| Estimated Fair Value, 12 Months or Longer                                                          | 2,902         | 456           |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 1,014         | 170           |
| Estimated Fair Value, Total                                                                        | 4,495         | 4,535         |
| Gross Unrealized Losses, Total                                                                     | 1,152         | 939           |
| Asset-backed                                                                                       |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 1,562         | 4,660         |
| Gross Unrealized Losses, Less than 12 Months                                                       | 79            | 565           |
| Estimated Fair Value, 12 Months or Longer                                                          | 5,128         | 2,093         |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 1,162         | 498           |
| Estimated Fair Value, Total                                                                        | 6,690         | 6,753         |
| Gross Unrealized Losses, Total                                                                     | 1,241         | 1,063         |
| Residential mortgage-backed                                                                        |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 680           | 1,406         |
| Gross Unrealized Losses, Less than 12 Months                                                       | 30            | 144           |
| Estimated Fair Value, 12 Months or Longer                                                          | 2,094         | 1,143         |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 569           | 303           |
| Estimated Fair Value, Total                                                                        | 2,774         | 2,549         |
| Gross Unrealized Losses, Total                                                                     | 599           | 447           |
| Commercial mortgage-backed                                                                         |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 273           | 1,167         |
| Gross Unrealized Losses, Less than 12 Months                                                       | 9             | 159           |
| Estimated Fair Value, 12 Months or Longer                                                          | 1,161         | 408           |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 267           | 96            |
| Estimated Fair Value, Total                                                                        | 1,434         | 1,575         |
| Gross Unrealized Losses, Total                                                                     | 276           | 255           |
| Other asset-backed                                                                                 |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 609           | 2,087         |
| Gross Unrealized Losses, Less than 12 Months                                                       | 40            | 262           |
| Estimated Fair Value, 12 Months or Longer                                                          | 1,873         | 542           |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 326           | 99            |
| Estimated Fair Value, Total                                                                        | 2,482         | 2,629         |
| Gross Unrealized Losses, Total                                                                     | 366           | 361           |
| U.S. Treasury and obligations of government-sponsored enterprises                                  |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 106           | 76            |
| Gross Unrealized Losses, Less than 12 Months                                                       | 1             | 1             |
| Estimated Fair Value, 12 Months or Longer                                                          | 21            | 16            |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 1             | 1             |
| Estimated Fair Value, Total                                                                        | 127           | 92            |
| Gross Unrealized Losses, Total                                                                     | 2             | 2             |
| Foreign government                                                                                 |          |          |
| **Debt Securities, Available-for-sale [Line Items]**                                               |          |          |
| Estimated Fair Value, Less than 12 months                                                          | 201           | 473           |
| Gross Unrealized Losses, Less than 12 Months                                                       | 9             | 26            |
| Estimated Fair Value, 12 Months or Longer                                                          | 436           | 78            |
| Gross Unrealized Losses, 12 Months or Longer                                                       | 47            | 17            |
| Estimated Fair Value, Total                                                                        | 637           | 551           |
| Gross Unrealized Losses, Total                                                                     | $ 56          | $ 43          |

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